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Rick Woods
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Ashen Light - Redux
      #5741340 - 03/18/13 06:18 PM

There was a thread going in the Lunar forum that got sidetracked to the Ashen Light of Venus (a subject much more suited to this forum). It was shut down, but it was actually just getting very interesting. The primary participants were Mardi (Photonovore) and Pete (Azure1961), who had a pretty lively debate going on.

I was sort of hoping we could take it up again here. Both participants are articulate, and hopefully things would remain civil and productive. Pete does not feel the Ashen Light is a real Venusian phenomenon; Mardi raised many questions about that stance, and suggests that the issue is far from resolved; and one poster noted seeing the Light personally.

Can we continue from there without anyone getting irate? We all just want to learn from each other, after all. Many's the time I've had a long-held belief changed by learning a serendipitous new fact.


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azure1961p
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Re: Ashen Light - Redux new [Re: Rick Woods]
      #5741458 - 03/18/13 07:08 PM

Lol, you're a sadist astronomer!!!

Pete


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buddyjesus
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Re: Ashen Light - Redux new [Re: azure1961p]
      #5741495 - 03/18/13 07:25 PM

haha

I think we can all agree that the phenomenon exists. It is the location of the phenomenon that is disputed(on Venus or in our brains.) I wish I had a scope with less CA so that I would have a chance at seeing it well.


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Re: Ashen Light - Redux new [Re: buddyjesus]
      #5741589 - 03/18/13 08:01 PM

ive seen it a few times myself over the years,but sometimes i think the brain causes some of it ,but patrick moore has also stated he an other good astronomers saw that as well.in daylight when the crescent is real big i saw it a few times over the years and the surface area was definitely darker on venus opposite the crescent.

Edited by ROBERT FREE (03/18/13 08:03 PM)


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Re: Ashen Light - Redux new [Re: ROBERT FREE]
      #5741600 - 03/18/13 08:06 PM

also at half phase i definitely noticed a slight darkening at the the terminator many times,but that can possibly be due to contrast effects or scattered light.a few of my friends also said they saw the ashen light at the gibbous phase.

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Rick Woods
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Re: Ashen Light - Redux new [Re: azure1961p]
      #5741629 - 03/18/13 08:16 PM

Quote:

Lol, you're a sadist astronomer!!!




Maybe. But the subject interests me, and it deserves objective discussion. This is the best place I know of to get intelligent opinions. (As well as goofy ones.)


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sage
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Re: Ashen Light - Redux new [Re: Rick Woods]
      #5741650 - 03/18/13 08:22 PM

well i would like only intelligent ones,an patrick moore as you well know did extensive research on this subject an had individual attestation from other astronomers viewing independently.in the seventies an early 80ties i spend a ton of time on venus an have saw some unusual activity near the cusps an real bright circles unmistaken but so far as the ashen light there is definitely a darkening notiecable in clear skies an in daylight just like our moon with earthshine,now what the causes are is debatable i agree.

Edited by ROBERT FREE (03/18/13 08:24 PM)


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azure1961p
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Re: Ashen Light - Redux new [Re: ROBERT FREE]
      #5741767 - 03/18/13 09:09 PM

Im going to sit this one out Rick. I have my own views, beyond that it just gets to negative to assert a negative opinion even when im positive in my negativity. It is a beautiful planet and one Sheehan mentions with heartfelt fondness { yesim still glowing from that book while waiting on my delayed shipment of his mars book}.

Pete


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sage
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Re: Ashen Light - Redux new [Re: azure1961p]
      #5741809 - 03/18/13 09:33 PM

do i think the ashen light is real.probably not, as venus itself is covered with clouds an its high reflectivity is most likely the cause.we rarely get to see the surface an there is a bunch of activity going on all the time.

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Rick Woods
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Re: Ashen Light - Redux new [Re: azure1961p]
      #5742197 - 03/19/13 02:25 AM

Quote:

Im going to sit this one out Rick. I have my own views, beyond that it just gets to negative to assert a negative opinion even when im positive in my negativity. It is a beautiful planet and one Sheehan mentions with heartfelt fondness { yesim still glowing from that book while waiting on my delayed shipment of his mars book}.

Pete




Well, looks like Mardi is, too. Too bad. I would have liked to know what evidence you've seen to make you so positive it's an illusion.
Healthy debate and comparison of information can benefit everyone, if they'll listen to each other.


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stanislas-jean
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Re: Ashen Light - Redux new [Re: Rick Woods]
      #5742300 - 03/19/13 05:27 AM

Regarding the Venus ashen light here is a link where a report can be found about.
http://hebergement-pdf.com/mypdf.php?n=158
Hope it is functionning.
All the references collected in the table sheet are drawings issued on the alpo japanese site
http://alpo-j.asahikawa-med.ac.jp/Latest/Venus.htm

it can be discussed the visibility of the this strange light eg the fact this was not collected by ccd but in fact what can be argued is the fact that the light levels (crescent and ashen light) are quite different sothat light glare becomes a main topic on the ccd chipset even with the use of an occulting bar.
At final this remains controversial and very strange.
Contracditory also as between observers quite different observations are collected but what it must be highlighted is the fact that episodic observation are unfruitful and a daily basis survey has to be performed for sure.
Good read, I donot pretend this a true overall status but it was tried lot of kind of observations in order to understand what is happening.
Light levels needs to be quantified by parallel investigations.
Stanislas-Jean


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azure1961p
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Re: Ashen Light - Redux new [Re: stanislas-jean]
      #5742371 - 03/19/13 07:34 AM

The evidence to me is that the ashen light effect can be reproduced artificially. Same thing that produces the Terby Whitespot on Saturn for example in that its an illusion of contrasts and the brain manufacturing information through suggestion. That and the only thing that could light up the night side would be in the infrared. A sustaining global lightening storm with a steady unchanging output or full hemisphere aurora is unlikely to impossible. These are my claims. Also its important to consider that CCD images in visible light are at least as good as the eye in many cases and hard proof would have surfaced by now - and Id applaud it. That Mardi wasn't even aware of CCD sensitivety good enough to routinely image the spokes on Saturn casts doubt in my mind that she isnt realuzibg how thorough these instruments are today and as a result how handedly something as common as the Ashen Light would have been captured. strong claims by individuals even with 80mm refractors and again frequently enough, would certainly have landed such a feature through a C14 with a CCD by now - or any common and effective lunar planetary imaging system. This is an immense hurtle to overcome in arguing in favor of the ashen light and the reports through any number of sized instruments.
If such a thing existed you'd have these beautifully detailed, albeit, unbelievably so , images coming from guys like Damian and such. Instead - what we've got is modern amateur planetary imagers making beautiful and detail nighttime hemisphere images of glows in the infrared - an impossible feat for any human to make visually. The trouble with the artificial ashen light model is that its subtle enough that if someone wants to ignore it to support a belief its possible.

I'm not saying anyone's nuts for seeing it, Im saying its an artifact of the eye brain interpretation.

Pete

Edited by azure1961p (03/19/13 07:45 AM)


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stanislas-jean
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Re: Ashen Light - Redux new [Re: azure1961p]
      #5742406 - 03/19/13 08:13 AM

Why not.
What is the Terby white spot on saturn? If you have some data about.
However regarding the report on reference you see many tests were performed also.
The use of an occulting bar (that occults all the cresent) set on the planet by a second observer and then observed whitout a reset on the whole image. Believe me the dark side appeared with a low light often with a coppered color appearance sometimes, reported by past observers also.
There is also the dark markings reported that suit also with some few ccd images.
IR images: frankly under 1µm wavelength this cannot be a thermal effect and a little also above this wavelength.
It is impossible to get light from the ground with the ground temperature given in the literature about (450°C).
This could be explanained if some chemical reaction is occuring under specific conditions (pressure, some gaz presence) that locally involve an higher physical temperature for being thermal. But which one?
Now the fact that ccd for the moment doesnot capture this dark side light amount is disagread by the light glare of the light crescent. What is obvious can be that the ccd chipset after an exposure time would reach a certain threeshold and therefore if the AL is existing its light level would be under the level of this threeshold reached. Nothing else. This threeshold is not noted.
Anyway, this should be developped and the observations needs to be more frequent.
The 50mm refractor observations are interresting on the fact that the light levels has moved sothat on a dawn light (the sky becoming dark) it was noted like a darker hole for the dark side on a date and for an other observation the dark side was seen lighted faintly. Observing with higher apertures the dark hole effect was never seen but a lighted dark side, almost at the similar moments.
That make me thinking this is a problem of light level accessibility only not depending on a specific colour channel vision.
But again, no enough data for a straight conclusion here.
Stanislas-Jean


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Re: Ashen Light - Redux new [Re: stanislas-jean]
      #5742505 - 03/19/13 09:42 AM

there is no doubt that the ashen light is seen,ive had so many reports from other amatuers an many real good observers an i also have seen it, BUT we will never know if does exist or what causes it.but there are other strange phenomenon like the real sudden bright spots that have popped up on occasions an these i think are real coming from what i dont know.many times i thought i saw a small break in the clouds during those white spot appearences,an at that time i was using a 12 1/2 inch f-8 reflector an high quality galaxy mirror.i had too stand on a ladder as well but it gave fantastic images so i know what i saw an others did too.im more interested in what happens on venus even if its only a glimpse sometimes, venus appears very active and maybe one day we will go there and use some probes or land but i doubt it in my lifetime.

Edited by ROBERT FREE (03/19/13 09:46 AM)


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stanislas-jean
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Re: Ashen Light - Redux new [Re: ROBERT FREE]
      #5742538 - 03/19/13 09:59 AM Attachment (18 downloads)

Reason why daily basis observations are needed.
Personally I noted some fluctuation of the AL level on a period. This is strange.
But even the AL was reported by observers even well known, I guess you see the below sketch for being sure of the AL occurence.
This is a processus a little hard for ourselves but this helps for being more confortable with the situation.
Stanislas-Jean


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stanislas-jean
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Re: Ashen Light - Redux new [Re: stanislas-jean]
      #5742547 - 03/19/13 10:07 AM Attachment (16 downloads)

You see the unknown settlement of the planet into the eyepiece equipped with an occulting bar by a second observer, is interresting to perform. The 1st observer will see or not something then if seen move the occulting bar to see if the crescent is in correspondance.
Hard.
The second sketch approaches the question of the light levels and is a support for the processus of light difference levels to capture. This is a trial because frankly I donot know if the light ratio of 1000 between the crescent and the dark side is adequate.
This is may a way to the solution.
Stanislas-Jean


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Re: Ashen Light - Redux new [Re: stanislas-jean]
      #5742775 - 03/19/13 11:57 AM

in mercurys case its most likely impossible to see any dark side because of the dimness of the planet in its crescent phase.even today its very thin phase illumination is 0.236 and its disk size around 9.5 at 1.0 magnitude according to the data an cannot be seen but in about 3 days or so at 9" disk size an say 0.7 mag is about the limit to see the thin crescent but not thin enough for any ashen light.but like i said before i doubt as well if any ashen light truly exists an is most likely an optical illusion or high reflective scattered light. an btw JEAN that was very informative an thx.

Edited by ROBERT FREE (03/19/13 11:59 AM)


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stanislas-jean
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Re: Ashen Light - Redux new [Re: ROBERT FREE]
      #5742991 - 03/19/13 01:39 PM

At final the japanese Alpo published the report.
Here is
http://alpo-j.asahikawa-med.ac.jp/kk13/v130318r.pdf
the drawings are on the same topics.
Hope this is an help and easier.
Stanislas_Jean


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azure1961p
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Re: Ashen Light - Redux new [Re: ROBERT FREE]
      #5743168 - 03/19/13 03:02 PM

Quote:

BUT we will never know if does exist or what causes .




Good news. We know its imaginary because it isn't recordable with the detectors of current day which wod have no trouble imaging such a contrast intensity. It'd be pedestrian. There's no overreaching mystifying deceptor - it doesn't exist.

There. Now you are truly Free.

Pete


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buddyjesus
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Re: Ashen Light - Redux new [Re: azure1961p]
      #5743554 - 03/19/13 05:45 PM

more food for thought. http://www.universetoday.com/94848/the-mystery-of-venus-ashen-light-2/

"The Keck 1 telescope on Hawaii reported seeing a subtle green glow and suggested it could be produced as ultraviolet light from the Sun splits molecules of carbon dioxide, known to be common in Venus’ atmosphere, into carbon monoxide and oxygen, but the green light emitted as oxygen recombines to form O2 is thought too faint to explain the effect. Another more likely theory is that multiple lightning strikes are illuminating Venus’ skies. Though the Cassini spacecraft flew by Venus twice on it’s voyage to Saturn and failed to detect the high frequency radio noise we associate with thunderstorms on Earth, in 2007 Venus Express did detect low frequency ‘whistler waves’ that can also result from lightning. It could also be the Venusian equivalent of aurorae."

Read more: http://www.universetoday.com/94848/the-mystery-of-venus-ashen-light-2/#ixzz2O...


my money is the keck telescope had a camera on it and not an eyepiece. My money is on it not occuring on Venus, but monitoring should be done any way. what is the harm in amateurs looking? I think it is also common for people to view the polar cusps and think it is ashen light.


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stanislas-jean
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Re: Ashen Light - Redux new [Re: buddyjesus]
      #5744504 - 03/20/13 04:41 AM

Interresting Buddy, this bring a lot on the subject.
Is there something was performed on Mercury from your informations with the Keck or some other big guns?
It is strange that on Mercury, from my observations, nothing such was reported. It is harder to observe Mercury but the reports are the reports.
I agree with you, more observationnal data are needed for making a straight conclusion.
Pete, the fact that with ccd chipset, if with 1s, 10s, 30s etc exposure time nothing is collected, this doesnot mean that AL is not existing but again that a certain amount of light cannot be captured with such exposure. Beyond 30s, light glare is very present and disturbing so that the capture method has to be very expected acurate.
Also the duality eye-ccd properties cannot be straightforward so easily.
Is there somebody who knows where to find ephemeris of the solar wind reaching planets (here for Venus)? or this is confidential.
Stanislas-Jean


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azure1961p
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Re: Ashen Light - Redux new [Re: stanislas-jean]
      #5745231 - 03/20/13 02:08 PM

You need to try some imaging Stan there is no hiding place with a DMK DBK Flea3 Toucam or the like. Your assumptions are more in line with Tri-X.

Pete


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Re: Ashen Light - Redux new [Re: azure1961p]
      #5745323 - 03/20/13 02:55 PM

Just 2 or may be 3 time more sensitive than mine in NIR.
Stanislas-Jean


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Rick Woods
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Re: Ashen Light - Redux new [Re: azure1961p]
      #5746852 - 03/21/13 03:03 AM

Quote:

there is no hiding place with a DMK DBK Flea3 Toucam or the like.




What on Earth makes you think that, Pete?


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stanislas-jean
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Re: Ashen Light - Redux new [Re: Rick Woods]
      #5746894 - 03/21/13 04:54 AM

The question of ccd collection is a sensitive point for sure.
However considering the document brought by Buddy, I noted a ratio cresecent dark side of 10 000 (means 10 magnitude difference probably on the O3 colour channel).
This ratio would involve some exposure times for collecting something of 10 minuts.
Having done some trials with a sony 098BL chipset, beyond 30sec this becomes hard to not be annoyed by the light glare even with the occulting bar use of D3 density.
So from my opinion this should not be the subject on this forum to say
this is an illusion
this is lightning
this thermal
this is water vapor dissociation
etc...
but if each is existing which light level could be expected and therefore to discuss which capture method can be undertaken.
Frankly imaging is not only a fact to set a chipset and to practice exposures (this is the prior first step of a method in order to start an apraisal only).
The links brought by Buddy are interresting because some light levels are expected and this goes on this approach at final.
If somebody wants to pursiue on that approach, please goahead, I will follow with open mind in order to built some assessment methods that can be undertaken for the next Venus conjunctions.
Matter of a forum!
Stanislas-Jean


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azure1961p
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Re: Ashen Light - Redux new [Re: stanislas-jean]
      #5746995 - 03/21/13 07:24 AM

Rick,

While there is greater dynamic range in vision, the ccd is ruthlessly effective in ferreting out details often invisible or close to invisible to the human eye. What it lacks in dynamic range which isnt much, it over compensates for in contrast boosting at levels no eye or brain can achieve. Add wavelet sharpening, saturation boosting and its pretty well drained the loche.

This same ability of the ccd to differentiate intensity, contrast and magnitude differences so well and beyond super human was well shown recently in a ccd image of Enceladus and Mimas beaming through the over exposed glare of Saturn. The differentian between Saturn and Mimas is well beyond 10 magnitudes Stan.

Pete


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stanislas-jean
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Re: Ashen Light - Redux new [Re: azure1961p]
      #5747053 - 03/21/13 08:20 AM

We could discuss about this assessment. I saw such images also performed with a 10" and satelites of 0.18" disk, dark shadow and clear disk on planet, overexposed saturn disk and 11th magnitude stelite also but not closed to the planet for avoiding the glare of light.
Also the AL with ccd images null but no visual data at the same time, etc... images with 1µm filter as well. This doesnot mean this is an illusion. It is needed more data and simultaneous data and numerous.
Keep in mind that it seems that Keck get light level on the dark side with the famous ratio of 10 000 in green/ O3 channel colour. This is a start.
But,
There is a proposal in my last post for something other than to get right. This is not interresting me.
And,
what is interresting is to built assessments as proposals for making after basis of observations and survey.
Stanislas-Jean


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azure1961p
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Re: Ashen Light - Redux new [Re: stanislas-jean]
      #5747550 - 03/21/13 12:45 PM

Stan,

You seem to counter point for the sake of countering in itself. There is no way in heck you can see Mimas like that visually in any scope. And its fainter than 11v. Sometimes I think you enjoy the game of debate more than the substance of it.

Pete


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EJN
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Re: Ashen Light - Redux new [Re: azure1961p]
      #5747637 - 03/21/13 01:24 PM Attachment (17 downloads)

This is my sketch of the crescent Venus. It should be considered definitive.

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stanislas-jean
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Re: Ashen Light - Redux new [Re: azure1961p]
      #5747756 - 03/21/13 02:43 PM

Keep in mind that venus is observed in dawn light for the best and not on full night as for saturn.
Useless to stay here more time.
Stanislas_Jean


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Re: Ashen Light - Redux new [Re: EJN]
      #5747764 - 03/21/13 02:47 PM

EJN good sketch with cusp extensions, without doubt reason why this is smiling.
Stanislas-Jean


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Re: Ashen Light - Redux new [Re: stanislas-jean]
      #5747835 - 03/21/13 03:21 PM

I'm inclined to doubt its reality. First, to have seen it in *daytime* means that it would have to be astonishingly obvious at night. The daytime sky is so very bright that in order to even begin to compete any extended source must necessarily be bright also.

If we take the daytime sky to have a surface brightness of, say, 2 magnitudes per square arcsecond, a source must be no fainter than 6 MPSAS if it is to be seen. This is about the same surface brightness as the sunlit surface of Neptune, which at night presents no difficulty at all, and moreover is more than sufficient to reveal color (the detection threshold of which is 18-19 MPSAS.)

In short, daytime observations of this phenomenon must certainly be illusory, for at night the effect would be glaringly obvious to all. And if the detection during the day is accepted as illusion, the possibility of its being so at night must be entertained.


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Re: Ashen Light - Redux new [Re: GlennLeDrew]
      #5747976 - 03/21/13 04:22 PM

Count me as a doubter. Has any spacecraft ever shown the light? I don't doubt people believe what they see, but that is not the same as the event or feature occurring

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Rick Woods
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Re: Ashen Light - Redux new [Re: LivingNDixie]
      #5748345 - 03/21/13 07:20 PM

Well, though, it evidently only shows up once in a while. There may not have been a spacecraft looking when (if) it happened.
Tom Dobbins was a doubter until he saw it for himself, per a recent S&T article by him. I've seen airglow, lightning, aurora, and glowing-hot surface proposed as possible solutions. I don't really understand why one or more of these couldn't be the cause of the phenomenon.


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Re: Ashen Light - Redux new [Re: Rick Woods]
      #5748477 - 03/21/13 08:37 PM

even though it is an aside, Mimas is visible visually, though I doubt as anything but a diffraction pattern.

Mimas was discovered by the astronomer William Herschel on 17 September 1789. He recorded his discovery as follows: "The great light of my forty-foot telescope was so useful that on the 17th of September, 1789, I remarked the seventh satellite, then situated at its greatest western elongation."[9]


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buddyjesus
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Re: Ashen Light - Redux new [Re: buddyjesus]
      #5748488 - 03/21/13 08:46 PM

my opinion of ccds is that they aren't quite there yet. This is based on seeing raw and computer manipulated images from scopes twice as big as mine in diameter that rival my 4" scope in detail. The light they collect is just too blurred during even the short exposures that they select for stacking.

I subscribe to the ALPO Venus newsgroup on yahoo and haven't seen images shared since I joined of anyone trying to image the dark side. Most of their best images are in UV of cloud bands on the lit side. I highly recommend this group for the quality images and because the group isn't super active and won't flood your mailbox.

Another thing to consider is that ccd imagers usually use uv/ir cut filters as standard fare. The human ability for some people to see near UV light is documented, though I haven't found anything that says people can see near IR.


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Rick Woods
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Re: Ashen Light - Redux new [Re: buddyjesus]
      #5748794 - 03/21/13 11:46 PM

Good post!

IIRC, in the other thread David Gray said he had unusually good eyesight in the near IR. (I could be remembering wrong.)

Whether or no, I'd never accept the results of a machine as a gauge of what is possible for a human. (At least, not a machine created by humans.)


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Edward E
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Re: Ashen Light - Redux new [Re: Rick Woods]
      #5748844 - 03/22/13 12:07 AM

I do not think there has been a good showing of the event since the early 1980s. I have been looking but have not since it since my late 70s/early 80s observation. As Jack Horkheimer use to say "keep looking UP!"

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GlennLeDrew
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Re: Ashen Light - Redux new [Re: buddyjesus]
      #5748851 - 03/22/13 12:15 AM

One can determine in advance the level of surface brightness Venus' night side much achieve, after considering such factors as the glare from the sunlit side, contrast-reducing light from twilight, airglow and zodiacal light, and atmospheric extinction. Taken together, these phenomena are not inconsiderable impediments to seeing any glow on Venus' night side.

The nature of the observations so far seems to me to practically dictate a planet-wide brightening, for the ashen light reports that I'm aware of are of an essentially uniform illumination of the entire visible portion of the night side. What phenomenon could be responsible?

Airglow in the upper atmosphere? It would necessarily be some orders of magnitude brighter than that surrounding Earth. And of course it would need to vary in intensity by a very considerable margin, in order to be not seen under otherwise optimal conditions and yet seen under awful conditions (i.e., daytime!).

Aurora? Could such surround the entire planet (or at least the entire night side?) That doesn't seem very feasible.

Lightning? The dense cloud would diffuse and attenuate any individual discharge to a very local glow. It would require to have essentially planet-wide discharge at high frequency and over relatively small separation to result in a continuous and uniform glow.

Sunlight scattering through the clouds and well into the night side? It doesn't happen on Earth, and so there is no reason to suppose it can do so on Venus.

One kicker for me is the fact that any such glow must compete with the very brilliantly sunlit cloud deck. In spite of the eye's huge dynamic range, the proximity of such an intense crescent in *immediate* proximity presents a source of scatter in both the optics and observer's eye.

In short, to be seen on Venus any night side glow would have to be rather more intense Earth's night side when moonlight is absent, and perhaps even with a bright moon illuminating it.


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azure1961p
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Re: Ashen Light - Redux new [Re: Rick Woods]
      #5748858 - 03/22/13 12:22 AM

Quote:

Good post!

IIRC, in the other thread David Gray said he had unusually good eyesight in the near IR. (I could be remembering wrong.)

Whether or no, I'd never accept the results of a machine as a gauge of what is possible for a human. (At least, not a machine created by humans.)




But Rick that's not fair to the technology. Look at deepsky for example - even a lousy CCD will handedly outstrip the best visual and its not a slam at visual, just a case where technology has surpassed it. I think at the arc second level - on lunar and planetary - the human eye is still the best in terms of contrast and such but broader angular seperated features I think fall well into the hands of CCD. It's scary how well it does on Enckes even in medium apertures (large).

I'm primarily visual. I think I'm 10% imager so I'm not trying to justify my bent for the latter - its pretty tame. But the evidence in even a 4" refractor on Jupiter is crazy good.

Doublestars though just aren't there yet in CCD. They need a lot more sensitivety for diffraction patterns in size and brightness difficulties.
Pete

Edited by azure1961p (03/22/13 12:24 AM)


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azure1961p
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Re: Ashen Light - Redux new [Re: EJN]
      #5748863 - 03/22/13 12:25 AM

Quote:

This is my sketch of the crescent Venus. It should be considered definitive.




I think it just may be.

Pete


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David Gray
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Re: Ashen Light - Redux new [Re: Rick Woods]
      #5749091 - 03/22/13 06:00 AM Attachment (19 downloads)

Quote:

Good post!

IIRC, in the other thread David Gray said he had unusually good eyesight in the near IR. (I could be remembering wrong.)

Whether or no, I'd never accept the results of a machine as a gauge of what is possible for a human. (At least, not a machine created by humans.)





Move over piranha I’m jumping in!

Hi Rick: yes I have said I am very (“freakishly?”!) red-sensitive. Never liked a red observing light but whatever colour the level needs to be right. I have an ordinary dimmable ‘white’ light on my 1968 vintage homemade drawing board as I do a lot of colour work, and is fine for any object: planets, DSOs etc at the right level.

I have reported the AL in the past and am attaching two impressions from 2007. The first I have to admit is pretty weird. Actually this was shown on BBC TV’s Sky at Night and in spite of my insistence/pains that the brightness/contrast levels should be maintained apparently the people involved seemed to want to use ‘artistic’ licence and it appeared on the screen far more garish than I have ever seen earthlight on the moon. Total embarrassment, they, and certain others, get no more from me! At the same time I can’t anticipate how others have their monitors calibrated; but some types (mine!) will need to be viewed square-on for these.

Due to our house obscuring much of the s’west sky I do not often catch Venus for AL at evening elongations unless it is north of declination +20 deg. This was the case last May when I caught the planet on a number of nights in near perfect conditions with the 415mm D-K. Apart from a possible vague (brownish?) shading twixt the cusps on one night saw nothing of the AL even when hiding the crescent and with/without filters etc – you name it. These views were mostly in a very dark sky.

It has been said that it is more commonly seen at evening elongations than mornings; but I think anyone looking at this statistically would have to take account of, among other things, lay-a-beds and stove-huggers!

Not sure if the attachments will come out ok so please bear with me if I have to edit!


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David Gray
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Re: Ashen Light - Redux new [Re: David Gray]
      #5749093 - 03/22/13 06:11 AM Attachment (18 downloads)

That's about right - here's the other!

With the very greatest of respect before anyone takes issue please read with care my message and notes on attachment. Having more than once been misread and even taken out of context(in the recent Uranus threads) and used as an apparent pretext to give me a lecture on honesty and observing procedure etc.......please......!


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azure1961p
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Re: Ashen Light - Redux new [Re: David Gray]
      #5749158 - 03/22/13 07:48 AM

Exquisite work David. Your technique is impeccable and I appreciate your observing skills. I've seen the AL - I just don't attribute it to a real phenomena on the planet itself. Great work.
Pete
Lay in beds and stove huggers


Edited by azure1961p (03/22/13 07:50 AM)


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David Gray
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Re: Ashen Light - Redux new [Re: azure1961p]
      #5749333 - 03/22/13 09:55 AM Attachment (18 downloads)

Quote:

Exquisite work David. Your technique is impeccable and I appreciate your observing skills. I've seen the AL - I just don't attribute it to a real phenomena on the planet itself. Great work.
Pete
Lay in beds and stove huggers





OK Pete – I’ll assume that you’re not being just a tiny bit patronising here – thanks!

It has been said/proven(?) that spider vanes can produce a false AL effect so I will rule it out in my case with the attached – secondary affixed to optical window.

Now: after I reported the AL to one-time BAA Section Director Richard Baum he subsequently passed back to me queries from John Westphal re. the state/quality of the filters and optical window. As reported back:-

Filters: were (are) in a pristine condition and often used on the moon, and shadow-filled large craters make a fair approximation to crescent Venus and would soon have been concerned if they were showing such internal illumination/light-spill. Rotating filters/eyepieces is another check of course.

Optical window: kept clean – and dew-checked often during a session. There is a slight ghost but this is offset a few arc minutes from the planet/s. Presumably it is slightly not squared on but I like to keep it that way so as not to interfere with seeking faint satellites etc.

Incidentally after getting the rather superb WO Amici and Meade 5000 Plossls, when Saturn was at a greater altitude with rings pretty wide open I started seeing Mimas quite regularly without hiding Saturn. Clean optics and good seeing essential here as well as transparency otherwise you get a situation as in M42 and some PNs where faint stars are faded/lost in poor definition giving illusion of variability (yes I know many are in M42!)

Here is a message to Richard which also details the recently posted AL obs.

From: David Gray
Sent: 27 September 2007 16:35
To: Richard Baum
Subject: Venus AL

Hello Richard,
Ashen light again but much more elusive than the [Sept] 23rd . A lot of cloud was appearing just as Venus became high enough. I attempted to eliminate some of the possible causes of any spurious effects but due to the conditions only managed to check out the Amici and the binoviewer - see attachment. The Amici is by Williams Optics, and is far superior to the Edmund's that I used since the early 80s. I can report that with the Williams and the bino combined I was routinely spotting Mimas near elongation last apparition [2006] and without hiding Saturn - indeed it often [irritatingly!] caught my attention whilst scrutinising the planet - without being sought. Also Enceladus often seen near its conjunctions with the globe [all later checked on Sky Map Pro].
Again I have copied the drawing by 'drawing/painting' it into Corel. I must, however, chance installing the scanner software as I am not happy by abusing my eyesight spending so long staring so intently at the monitor. I feel that this can affect the vision for critical planetary observation. Years back I got hooked on playing chess for hours on the PC, and I am sure that this took the edge off my acuity, and for some days/weeks after realisation and packed it


If real it is apparently very transient - we need to keep looking (also at Uranus!!)

David.

Edited by David Gray (03/22/13 09:59 AM)


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azure1961p
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Re: Ashen Light - Redux new [Re: David Gray]
      #5749516 - 03/22/13 11:46 AM

Oh not at all, I was patronizing in spades lol. I'm a fan of your work - particularly your Galiean moon drawings. I like that you weighed in on this despite my own experiences.

Mimas I know is visible to amateurs with large scopes. I'd like to make it happen in my medium reflector. In mentioning it I was not implying it was off limits but that the CCD despite the wash of glare from Saturn brings it out with great clarity in a way the eye cannot perceive it. The thread Saturns Moons in this forum has a pic imaged through a ten inch aperture of Mimas that shows it quite clearly. I was using it as an example where dynamic range if lesser can be off set by contrast manipulation.

Best,

Pete


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photonovore
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Re: Ashen Light - Redux new [Re: azure1961p]
      #5751951 - 03/23/13 01:50 PM

Just a stray thought...There is another possible mechanism for Venusian ashen light, that being the earthshine during periods of high combined albedo of the earth/moon system. Lest one declare this idea (not mine BTW) unrealistic, consider that Venusian light (at crescent phase) is strong enough to cast shadows detectable by the human eye. (Even Jupiter has been documented as having the power to cast detectable shadows!) Oppositely, the earth at the same time is illuminated from a Venusian perspective at a gibbous phase and has ~10% more area overall in addition. Earth's albedo is generally considered to be half that of Venus, but greater illuminated area (gibbeous vs. crescent) would make the Earth at least as bright as seen from Venus than Venus as seen from Earth.

re; CCD, mimas saturn is an invalid analogy for the ashen light case as the former deals with a point source of high per pixel intrinsic contrast where the latter is dispersed over a large area giving a significantly lower sum contrast ratio--and thus a significantly *higher* contrast ratio with the illuminated source. Comparison of illumination per unit area between the two primary target areas is the controlling factor and when one is intrinsically low and the other extremely high, this makes for a perfect storm of high dynamic contrast, where the ccd remains utterly inferior to the human eye. HDR methods have issues due to blooming vis a vis target size. I wonder what the magnitude record is for capturing a star occulted by the Venusian darkside? In the observing record i find that the limit visually was supposed to be between 8 and 9th magnitude.

Still, lack of imaging evidence remains the best argument for ashen light being an illusory effect. However, the observational record argues against illusion because of the intermittent nature of the observations. An illusion is typically reproducible and consistent across large populations, given conditional restraints (ex. moon/horizon illusion). However, ashen light observations are anything but..being very inconsistent in both occurrence and across populations- and this would argue against it being a garden varity illusory effect.

As earth's albedo varies a good deal with the current weather on the sunlit side plus seasonal variability, and also considering concurrence of fuller phases of the Moon (from a Venusian perspective) in conjunction with anomalously high earth albedo periods, the moon/earthshine hypothesis seems sort of appealing to me as a possible explanation at least. there also remains the possibility of a combination of effects; intermittent Venusian atmospheric phenomenon plus extant earthshine.


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Re: Ashen Light - Redux new [Re: photonovore]
      #5752019 - 03/23/13 02:37 PM

Did you exercise some calculations regarding this assessment?
My expectations conduct to get a light level ratio of largely more than 10 000x between the crescent and the dark side levels.

Agree with you concerning the meaning of the dark side light accessibility being a surfacic light level to be captured and to be on comparison. Nothing to see with a pin point star/satelite with light levels, perceptibility access is not on the same level. The time of observation is also a disturbing parameter in regards because the light levels difference becomes narrower, crescent, dark side (not black hole appearance) and backgroud sky of blue, deep blue, dark blue, never black.
The results, I reported for AL captured, during day, dawn and just after sunset would conduct to get an intensity not confidential or negligeable. This needs confirmation indeed.
Stanislas-Jean


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Re: Ashen Light - Redux new [Re: photonovore]
      #5752206 - 03/23/13 04:13 PM

Excellent comments, Mardi. And Stanislas-Jean.

Regarding Earth/Moon shine. One could calculate the maximal integrated magnitude of our 'dual planet' as seen from Venus. Then the illumination level on Venus' cloud tops could be compared to that of Venus on Earthly snow; both surfaces have reasonably similar albedo.

For my own observations, -4m Venus shining in a dark sky on snow casts a not terribly obvious shadow, the latter being filled in to some extent by the -8m light of the night sky (air glow, primarily, augmented to some extent by stars, Milky Way and zodiacal light.) If not for these other bright sources, Venus' shadow would be rather apparent due to significantly higher contrast. (But the overall illumination would of course be less.)

For Venus we will have the following contributors to its nighttime illumination:
- Stars; -4m
- Milky Way; up to -5m
- Zodiacal light; -5m
- Earth (and Moon, which contributes very little due to 1/16 the projected area and 1/3 the albedo); -4m (?)
- Venus' own air glow; ?? (If present and of similar intensity to that of Earth, its surface brightness against the orb of the planet might be something like 22 mag/arcsec^2.)

(Regarding my provisional guess for Earth's maximum apparent magnitude as seen from Venus. While it's a bit larger the Venus and is always at least at gibbous phase, its albedo is 1/2 or a bit less, and it's farther from the Sun, receiving less than 1/2 the light.)

If we integrate all these sources (neglecting for the moment any Venusian air glow), we get around -6 to -6.5m. If we assume an air glow layer like ours, the total irradiance would be much like that here on Earth, it being around -8m.

The question then becomes this. Can a nighttime illumination like that of snow on a moonless night out in the country be seen when:
- Some fraction of the sunlit planet is immediately adjacent?
- When the contrast is reduced by intervening terrestrial air glow (or, worse still, twilight glow if the observation must be made with the planet well enough above the horizon)?

Out in the country, a snowscape had a surface brightness very nearly equal to the integrated light of the night sky, which is 21-22 mag/arcsec^2, and as noted be can take Venus' night side to have a surface brightness of this order. The sky against which we see Venus is always brighter than this, it being hardly ever darker than 20 MPSAS. If Venus' night side is, say, 2 magnitudes darker than the sky, its light and that of the sky combined makes that surface appear 16% brighter than the surrounding g sky.

A not terribly low contrast, but not a very easy detection, either. *Especially* with that blazing -4m crescent--with a surface brightness higher than sunlit snow--up against it! And considering that the exit pupil tends to be on the small side in order to achieve sufficient magnification, this dims the view and by itself makes that low contrast view of the night side against the sky more difficult still.

Why there is doubt regarding the utility of electronic detectors to image here what the eye supposedly sees astonishes me. If the ashen light is real, an imaging system of no great sophistication will reveal it, when a suitable exposure is employed. If the light scatter from the sunlit crescent is no impediment visually, neither will it be for a camera.

Finally, I do wonder if something along the lines of the Martian canal phenomenon, in 'reverse', if you will, might not be in operation??

The foregoing provides a line of reasoning to build upon for the determination of a likely Venusian night side surface brightness required for terrestrial detection. And from these considerations I am currently quite doubtful of the reality of the ashen light.


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David Gray
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Re: Ashen Light - Redux new [Re: photonovore]
      #5752222 - 03/23/13 04:20 PM

I recall Patrick Moore giving serious consideration of Earthshine as being a possible cause for AL in the BAA Journal but I believe he decided against it in later years. I understand that a near full Earth would be as bright as mag. at least -6 and the moon similar to how we see Jupiter. Jupiter from Venus would not be a lot fainter than we see it – should this be factored in? Perhaps so, but only when it is suitably positioned in relation to Venus and does this provide the ‘tipping’ point to render AL visible to us? I think not really: Jupiter + moon would only add fractionally to Earthshine.

With earthshine we perhaps expect AL to be bluish or simply grey, but it is most often described as reddish/brownish (even purple!); and this more accords with my filter experiences (W#22: Orange). But using W#23A (light red) I feel it is disproportionately more elusive and very fleeting at best in the denser W#25 (red). This colour impression I feel somewhat works against the illusion explanation. I agree if it was pure illusion it should be more consistently seen than reported; and more likely smooth than mottled.

Has it been (can it be) ascertained, I wonder, if the reflectivity – the very nature even – of Venus’ atmosphere increases(?)/changes on the night-side as another line of thought?


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Re: Ashen Light - Redux new [Re: David Gray]
      #5752265 - 03/23/13 04:41 PM

Discussions such as this can be Googled:
http://cosmoquest.org/forum/archive/index.php/t-63462.html

Edited by David Gray (03/23/13 04:45 PM)


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GlennLeDrew
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Re: Ashen Light - Redux new [Re: David Gray]
      #5752290 - 03/23/13 04:52 PM

If Earth light were dominant, the color would be only a *pale* bluish, due to the higher reflectivity of the clouds vs the ocean. Close enough to white to make blue filters likely detrimental due to their attenuation of that non-blue light contributing greatly.

The appearance of a reddish hue (or any color, for that matter) is almost certainly illusory if the surface brightness is below the color detection threshold of about 19 magnitudes per square arcsecond (as *perceived*, taking into account image diminution from a smaller exit pupil). Contributing to the reddish hue *might* be the well known phenomenon whereby dimmer parts of a scene take on a warmer hue.

I should think the characteristics of the cloud cover are of the normal, expected variety, with no peculiar reflectance at night vs day. Nor is the scattering markedly skewed over the visual spectrum, as evidenced by the pretty neutral white under sunlight.

Anomalous reflectance (or emission) outside the visual spectrum can hardly be expected to elicit a visual response. This is certainly where the expanded spectral sensitivity of electronic detectors affords a decided advantage over the eye.


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Re: Ashen Light - Redux new [Re: GlennLeDrew]
      #5752329 - 03/23/13 05:18 PM

Agreed in principle, but personally I have never seen it in other than the filters reported in the above observation attachments; so can't attest to any hue! That is never have I detected it in intergrated light; and presumably it has, as alluded to in my above reports, been rendered visible by: "This [filter] combination rendering the sky almost black." (Sept 23) and in addition conceivably dimming the bright crescent relatively more than the presumed AL??

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Re: Ashen Light - Redux new [Re: GlennLeDrew]
      #5752334 - 03/23/13 05:24 PM

David,
I checked out the discussion you linked to. It was interesting to see a number of congruencies with my own line of reasoning conducted in isolation. It seems my 'gut feeling' of -4m for the Earth as seen from Venus is rather less than the -7 bandied about in that discussion. I should calculate it myself, if for no other reason than to refute my incorrect mental image.

That notwithstanding, a -7m Earth (augmented by the other sources I enumerated earlier) will still result in a cloud deck on Venus' night side having a surface brightness hardly brighter than 20 mag/arcsec^2.


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David Gray
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Re: Ashen Light - Redux new [Re: GlennLeDrew]
      #5752388 - 03/23/13 06:01 PM

Quote:

David,
I checked out the discussion you linked to. It was interesting to see a number of congruencies with my own line of reasoning conducted in isolation. It seems my 'gut feeling' of -4m for the Earth as seen from Venus is rather less than the -7 bandied about in that discussion. I should calculate it myself, if for no other reason than to refute my incorrect mental image.

That notwithstanding, a -7m Earth (augmented by the other sources I enumerated earlier) will still result in a cloud deck on Venus' night side having a surface brightness hardly brighter than 20 mag/arcsec^2.




Glenn,
Fully agree: as indicated in my earlier post, that Earthshine is a non-starter.

I will, of course, keep checking the planet out but realistically my observatory is not that well placed for the already difficult pursuit of systematic AL study/detection. Too many seasoned observers (some initially sceptical) have reported this to walk away crying illusion, illusion!

Cheers,
David.


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stanislas-jean
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Re: Ashen Light - Redux new [Re: GlennLeDrew]
      #5752439 - 03/23/13 06:25 PM

We could conclude for a combination of "effects" that produce this possible AL.
Personnally at present I am sure of the presence of no effect.
The light reflection from the planets producing a light level on the dark side which is reflected also by the dark side atmosphere to us is hot to hold. The overall status will be poor and quite depending on the localisation of the planets respectively. This cannot occur on a long period may be few days.
The problem is that this reported over months before after conjunction.
Personally for the last conjunction this was collected from phase 0.35 until almost 0 with strong fluctuations of light intensity.
This is not observed in a colour more than an other colour channel, the blus channel seems to reveal also AL.
The intensity seems not to be depending on time moments from day until dawn and after sunset (but not black night).
The peak intensity was noted 30 days before conjunction and 15days after. Around the peaks of intensity fluctuations were observed, dark features were noted that seemed to be in relation with those collected by others with ccd.
I found this interresting but not enough by the number of data collected.
Systematically it should be used filters from the blue until the red and no filter, should be on observation at different moment in order to assess the background intensity of the sky for comparing with the observationnal data.
Daily basis observations should be done.
This will help to know:
- if this is transcient, I donot believe this,
- if fluctuations will occur again,
- when peak intensities will survey again,
_ the influence of sun activity.
It is easy to undertake such.
But before the observation method should be clean.
Occulting bar may involve diffraction edge with a light intensity "grainy", at final with the test practiced with a second observer i decided to donot continue the use of occulting bar. But i decided to use a second aperture in order to modify the respective light levels, a R50mm and a 200mm, 100 and 150mm used usually.
It's not simple to state but the method must be clean and absolutly sure.
Because we can be under an observationnal artifact , not under the pseudo illusion of eye limitations set by some. This aspect has to be well verified but how?
Stanislas-Jean


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buddyjesus
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Re: Ashen Light - Redux new [Re: stanislas-jean]
      #5752500 - 03/23/13 07:10 PM

I think the earthshine idea is a no go based on your approximations Glenn, but also must based on the inverse square law.

http://en.wikipedia.org/wiki/Inverse-square_law

What I think is most likely is the contrast effect that the area closest to the lit segment appears extra dark like the areas near the martian polar caps. Then the rest of the dark disk doesn't look as dark in comparison. Just a thought I am throwing out there to be bantered.

I think suggestion of it being there also tinges our ability to be blinded appropriately to trust our eyes.


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Re: Ashen Light - Redux new [Re: buddyjesus]
      #5752513 - 03/23/13 07:15 PM

here is a link to the article about suggestion and observation. http://www.skyatnightmagazine.com/feature/column-excerpts/seeing-believing-%E...

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Re: Ashen Light - Redux new [Re: buddyjesus]
      #5752729 - 03/23/13 09:12 PM

Quote:

What I think is most likely is the contrast effect that the area closest to the lit segment appears extra dark like the areas near the martian polar caps. Then the rest of the dark disk doesn't look as dark in comparison.




Yet, the dark Martian polar cap collar is a physical reality.


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azure1961p
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Re: Ashen Light - Redux new [Re: Rick Woods]
      #5752807 - 03/23/13 09:48 PM

The earthshine is a stretch (of millions of miles actually) but its a compelling notion. It would be interesting to model this out and I don't see why a msgnitude surface bright was couldn't be worked out for such a known reflective surface.

I'm still deep into the idea its not a true physical phenomenon of this world but earthshine is the first thing that actually holds some plausible notions.
The red color if its true would seem to be a contrast from a grey area playing opposite the contrast of a blue of blue/indigo sky. The light needed to illuminate it though from our planet... It'd be more plausible if our planet were Jupiter.

Mardi you are disagreeing with me for the sake of form and Im not addressing it. It's enough at this point.

Pete


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azure1961p
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Re: Ashen Light - Redux new [Re: Rick Woods]
      #5752832 - 03/23/13 10:00 PM

Quote:

Quote:

What I think is most likely is the contrast effect that the area closest to the lit segment appears extra dark like the areas near the martian polar caps. Then the rest of the dark disk doesn't look as dark in comparison.




Yet, the dark Martian polar cap collar is a physical reality.




It is I agree Rick but I wouldn't doubt an effect at times to help it. Not always but sometimes perhaps. A reverse effect Ive seen is a Maria giving an impression of a polar cap that wasn't visible.
It was on a 5" mars - total illusion caused by Maria encircling a lighter toned polar hemisphere but the pole was tilted away.

Pete

Edited by azure1961p (03/23/13 10:02 PM)


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Re: Ashen Light - Redux new [Re: azure1961p]
      #5753011 - 03/23/13 11:41 PM

http://en.wikipedia.org/wiki/Lateral_inhibition

we are both right. This is from ALPO



NORTH POLAR REGION

The dark banding, the so-called "Lowell Bands," that can often be seen surrounding the polar caps during retreat is thought to be caused by formations of hoarfrost at the edge of the polar cap. This rough or textured material lowers the reflection of Sunlight from that area of the surface and could possibly darken the surface adjacent to the polar cap. Any suggestion that damp, melted water ice from the polar cap causes this phenomenon is unfounded. In addition, from the perspective of Earth-bound observers the brilliant reflection from the polar cap next to a darker surface material will cause a "contrast effect," as we observers refer to it. When very bright objects are placed next to duller, material we tend to see a band separating the two darker than it really is. Irradiation in the human eye is another cause for this phenomenon (See Figure 3-1).


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Re: Ashen Light - Redux new [Re: buddyjesus]
      #5753285 - 03/24/13 05:25 AM

Just wanted to share a paragraph from Sir Patrick Moore's Guide to Mars dated 1956(the edition I am reading) p37-38

Quote:

From a theoretical point of view Lowell's argument is perfectly sound. everyone knows that the caps do melt rapidly with the onset of summer, and no carbon dioxide deposit could possibly show a deep blue band such is that described by Lowell. It could only be produced by a shallow temporary sea, or by extreme "marshiness", persisting for some days in any one area before drying out. However, other astronomers cast grave doubts upon the actual existence of Lowell's band. Schaeberle, for instance, stated categorically that it was an optical effect due to contrast between the glittering poles and the dimmer, ruddy desert areas nearby. This was also the opinion of Antoniadi, who wrote in 1930: "The illusory character of the band in question was first recognized by Schaeberle. I have confirmed this theory by observing that it does not follow the laws of perspective, and that it cannot be photographed."

As to the apparent existence of the dark band, there can be no doubt at all; it can be seen with a very small telescope. On the other hand we know that the human eye is easily deceived, and it is dangerous to jump to any hasty conclusions.

Once again, recent investigation have gone a long way towards clearing up the problem. Dr. Gerard de Vaucoulers, who carried out an intensive study of Mars at Le Houga Observatory in 1939, considered that although contrast effects were partly responsible for the darkness of the fringe, the band itself was "a real phenomenon, not a sheer illusion", and this is also the opinion of Dollfus, who has been studying the problem from the clear heights of the Pic du Midi. Even more definite views were expressed by Dr. Kuiper, in 1950, as follows: "I observed it with the 82-inch reflector under excellent conditions in April 1950, and found it black...The rim is unquestionably real; its width is not constant, and its boundary is irregular." Although Lowell probably exaggerated the blueness, it must now be considered certain that the band is not a mere optical effect. Now that we know the nature of the caps, there is indeed no mystery about it. As the cap melts, a certain amount of water is released: this moistens the ground, causing it to assume a temporarily darker hue until the moisture evaporates into the thin cold air and the marshiness disappears.




sounds definitive to me. Everything that is old is new again.


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Re: Ashen Light - Redux new [Re: buddyjesus]
      #5753349 - 03/24/13 07:38 AM Attachment (9 downloads)

The dark collar circling the polar cap is actual and not an illusion or some diffraction effect etc...but actual and sufficiently imaged for being obviously sure. Presently this was observed also with from 76 until 305mm. What is interresting to note are the condensations on that dark collar because from an opposition to the following some storms are borning from these condensations mostly.

Returning on Venus AL I propose you the below sketches in order to discuss about the observationnal conditions. From an observer to another there are "recettes" about that should work more or less. With regards to the light intensity level expected or observed we must be absolutly sure of the method in use.
The use of an occulting bar or side (that occults one side in the FOV at the eyepiece is seducing at the 1st approach.
When you test the system as for sketch 1 with modification of the shift it may appear visually this effect, subtil.
But with an intensity repartition not homogene.
Situation 3 get this effect, situation 1 nothing and situation 2 must be settled in order to avois or minimise the effect.
Considering now the sketch 2, considering situation 2 of sketch 1 well settled, with the help of a second observer, the second observer locate the planet as described behind the occulting bar of very dark density, observer 1 doesnot know where the planet is (situation 1, 2 or 3 of sketch 2)and try at final to identify the presence of AL.
After observer 1 is making the same inverted procedure for stating the disparition of AL or maintained.
I did this kind of test 2 times on 2 days when AL was reported without this test procedure.
I feel it is a way for being more sure and for being obvious in what is reported. At final I discarded the use of the occulting bar thinking it useless.
Trial test were done by ccd also and if diffraction edge effect was not seen, this became still prent at from some exposure times.
So if some test improvements were conducted this remains still not absolute.
I tried also to set the occulting bar with a little offset (the edge being not exactly at the eyepiece FOV focus plan).
The results were a little worst.
This is where I am, with less uncertainties but with still a certain amount.
I am still convinced that the observationnal conditions and method has a main influence on the results.
Who knows where to find a device without diffraction edge effect?
Sketch 3 is for illustrating the appearance of the planet at the eyepiece NS celestial axis is tilted from the XY axis exhibiting the "meridian" built by the crescent. It is needed the tilt of the occulting bar with regards to the crescent, easy to do. The shift of few arc seconds between the bar edge and the crescent cusp can be performed with the eq mount moving it with 1.25x the sideral rate in less during a certain time. Not hard to do.

Earth solar light reflection on the Venus dark side would be with regards to the distance 40millions kms difference and moon 0.4 millions kms will do a ratio distance of 100. Light intensity decrease with go with the square of the distance so at final 10000x less than the moon AL (10 magnitude less considering perfect reflection for each planet atmosphere).
So what remains for venus on dark side? on a long period?
Stanislas-Jean


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Re: Ashen Light - Redux new [Re: buddyjesus]
      #5753697 - 03/24/13 11:11 AM

Quote:

here is a link to the article about suggestion and observation. http://www.skyatnightmagazine.com/feature/column-excerpts/seeing-believing-%E...





I would take Moore’s comments about Richard Baum drawing canals a-la Lowell here with a large pinch of salt: Richard has on several occasions told me of his irritation at Moore mis-representing him. In fact this may well be such a one – I have several hundred e-mails from Richard (and pre these many snail-mails) but perhaps can track this down!


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Re: Ashen Light - Redux new [Re: David Gray]
      #5753746 - 03/24/13 11:33 AM

I have not yet spotted the Moore/Mars matter I just posted about. But Quickly found this exchange between Richards Baum & McKim:-

[2009 Mar 10]…………Conditions have not favoured Venus observation. A view in reasonable conditions last Thursday left me with an impression of extended cusps, certainly greater than 180 degrees. Also had an exchange witrh Richard McKim about the AL. You may be interested in what I said along with Richard's response; Here first is mine:

**All the excitement engendered by Frank Melillo's image of the dark side - presupposing it is not an artifact - has caused me to drag out my large archive on the subject, and to give it further thought. Bill Wilson has been looking as you know, but on reading my paper about M B B Heath's series of observations he has had his professional knowledge ignited and has been in touch as will be revealed further on.

I recognized long ago (1956) that visually there could be a link between the optical nature of Earthshine and the Ashen Light of Venus.

First we need to consider Earthshine and how it is presented. If the crescent Moon is picked up on daylight sky all one sees is a thin trembling crescent. No hint of darkness between the cusps. With the approach of twilight that region darkens but in a feeble manner, proportionate to the intensity of sky brightness and continues to do so until after the sun has set at which time one is left with an impression that it is neither darker or brighter than the sky. Once the sky darkens so earthlight emerges but by degrees.

Back in the 1950s three observers M B B Heath (BAA Saturn Director), Tommy Cragg, (Mount Palomar), and myself independently noticed the dark side of Venus undergoes the same sequence of visibility. Accordingly after examining many records -- hence my 1957 paper in the JBAA -- I published a short note drawing attention to this diurnal cycle. I noted it consists of three phases, (a) The Dark Phase when the night side appears darker than the surrounding sky -- subdivided into pre-sunset for eastern elongations, post-dawn for western. (b) The Neutral Phase, a transient equalization of dark side and surrounding sky, which observation seemed to indicate occurs when the sun is about 6 degrees below the horizon roughly 30 minutes after sunset dependent of course, on the character of the surrounding sky (whether cloudy or not etc.,), and (c) The Bright Phase, the true Ashen Light which varies in colour.

Bill Wilson's reaction on reading my paper about Heath's Venus AL observations is this: " I’ve just stumbled on the above paper of yours, "The visibility of the dark side of Venus 1921-1953" during late night reading of the journals. Wow! Everything clicks into place. The dark side, darker than a daylight sky and the dark side lighter than a twilight sky must, surely, be complementary aspects of the same phenomenon. I’m abruptly reminded of my visual optics: “Photopic” and “Scotopic” vision. Maximum sensitivity of the retina shifts from yellow to yellow-green as dark adaptation sets in. - 550nm to 510nm . I haven’t worked through the argument yet, but I’ve a hunch that this could resolve the paradox." 06/03/09

All this applies to the optical character of the phenomenon. My note is in JALPO 10 (1956), 11-13. Typically no one seems to have noticed it!

As we realise Frank M has registered thermal radiation, something the late David Allen demonstrated in his paper in 'Nature' years back. In fact David and I were due to collaborate on a paper. I was to tackle the historical side, David the modern view. Sadly it was not to be. The true character of the Bright Phase the AL proper however, must remain questionable although I seem to recollect US investigators claimed to have detected a feeble dark side glow a few years back.

You are right to suggest that it has not been registered by imagers because they observe when the planet is high in the sky, ignoring lower altitudes as then the seeing is not so good and the sky is too dark. Perhaps one of these clever people will come up with a method that gets round the problem.

It would indeed be good news if conditions were such on one occasion to allow that. As Alexander said of the outer ring of Saturn this is a Loch Ness of a phenomenon that continues to haunt every generation. Sobering thought that those early observers of Saturn's fourth ring were proved correct. Somehow I do not think the AL is to be confined to one chapter of the continuum that is the ongoing story of astronomy, rather like the mythical Vulcan it refuses to rest, as now we have professionals searching for vulcanoids!

As to the projected list of observations. The glow is the main list, but I may index what I have on the darker than sky aspect. This is a situation when in the end every bit of information could turn out to be useful. To reject observations now on a subjective basis would I feel introduce prejudice into the scheme of things. **

McKim to Baum:

**Many thanks. Yes, I am supposing that the imagers don't like a dark sky and bad seeing. There may also be a mental barrier. It is not just a question of waiting for a brighter image, for that is not wanted, but we must wait till the scattered light from the foreground sky is less intense than the AL itself. David Allen put it well when discussing the IRTE in the Yearbook of Astronomy once. “The voyeur in daylight is hindered by the reflected light from the net curtain being brighter than the contents of the room beyond. After dark......” I think this point somehow hasn't reach every imager. As I showed in my note on the AL at the 2007 W elongation, the images are simply not getting taken in a dark sky: only one date was there when visual and imaging work apparently contradicted, and for me the question of AL is open only in the sense that I await actual images of it which I know will ultimately come. **

Baum to McKim:

**
The reason I mentioned that note of mine from 1956 is simply this. The manner in which earthshine is presented throws an interesting sidelight on our perception of the Ashen Light of Venus. Most observers report the phenomenon as darker than the surrounding sky. The idea this is wholly illusory may only be partially true since it depends at what time the observation was made. I suspect a lot of observers look in bright twilight which is when earthshine is just beginning to show but as darker than the surrounding sky. I have verified this on a number of occasions as indeed has John Westfall. So because of the time the factor it may be incorrect to categorize all such reports as illusory.**

McKim to Baum:

**You may be right, but if the dark side does not become bright once the sky is dark, then it has to be illusion.**

Baum to McKim:

**Tommy Cragg as I recall did see just that. My records are not comprehensive enough nor my position good enough to attempt a sustained watch. I am either way in the matter just pointing out possibilities. It may be that illusion is involved along with reality. Earthshine always shows to me at least a darkness between the cusps. I have made numerous observations to that effect which is why I have a nagging feeling there is a tenuous link between the two appearances.**

McKim to Baum:

Thanks. I like your point that illusion and reality are mixed. I have not studied the Earthshine systematically like you and I will have a look sometime.

I have always assumed that the reddish tint of the (Venusian Ashen Light) phenomenon could have the tendency to make the true AL appear darker than the sky on a blue sky background, but it is a bit of a circular argument because if the AL is truly grey, it would appear to have a warm tint by subjective colour contrast with the blue, in the same way the predominantly grey martian maria look greenish or bluish by contrast with orange deserts. The other factor to be recalled is that the Moon always looks darker than the sky during a total solar eclipse, and this too is just contrast. This seems quite a good analogy given the thinness of the crescent during most AL reports.**

As you can see David, new doors opened on an old problem. It is worth looking at Earthshine. A phenomenon we take for granted but rarely examine in detail. I've kept it in sight for forty odd years and long ago was struck by the similarity it shows to the AL of Venus. I hope the message from Melillo gets through as it is most fascinating. Very best,Richard


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Re: Ashen Light - Redux new [Re: buddyjesus]
      #5753926 - 03/24/13 01:01 PM

Quote:

I think the earthshine idea is a no go based on your approximations Glenn, but also must based on the inverse square law.

http://en.wikipedia.org/wiki/Inverse-square_law

What I think is most likely is the contrast effect that the area closest to the lit segment appears extra dark like the areas near the martian polar caps. Then the rest of the dark disk doesn't look as dark in comparison. Just a thought I am throwing out there to be bantered.

I think suggestion of it being there also tinges our ability to be blinded appropriately to trust our eyes.




For the record, I didn't say either the collar or AL existed, just that we have to keep in mind optical effects that exaggerate our ability to see details, real or fantasy.

One thing that doesn't jive with the lateral inhibition idea with AL is the shapes sketched of it. If only lateral inhibition, wouldn't the AL follow the same arc as the crescent?

David, my research in AL agrees with observations mentioned in your correspondence. The AL is reported more frequently in the evenings and near inferior conjunction.


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Re: Ashen Light - Redux new [Re: David Gray]
      #5753938 - 03/24/13 01:05 PM

stanislas-jean, thanks for sharing your experiences with placing the occulting bar. I was thinking of making one with the bar off to the side but will not now.

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Re: Ashen Light - Redux new [Re: buddyjesus]
      #5753978 - 03/24/13 01:22 PM

The shapes of the ashen light in various patterns is another issue that debases the validity of the planet physical nature of this thing. Some observers see a smooth generalized glow while others see splotches and spots. One CN contributer sketched cloud patterns representitive of earths weather patterns. Adding to that the *ability* of some small refractors in resolving such a thing but large reflectors failing and the the whole thing becomes problematic and suspiciously murky.

Its regrettable that such a thing might preoccupy observing time rather than something with a greater sense of progressive discovery.

Referring back to earthshine again , like CCD detection in its clarity, the question of wether or not it is infact earthshine on venus can be calculated . We h ave reflectivity values, orbital data and so it could probably be answered with decimal point precision and magnitude per square arc second.

Pete


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Re: Ashen Light - Redux new [Re: buddyjesus]
      #5753984 - 03/24/13 01:24 PM

What i had noted about the post regarding the eathshine hypothesis, light ratio would be 1/1 000 000 or 0.001 cd/m2 for an AL level.
This is supposing the planets excellent reflectors not sphere surfaces without albedo ratio.
This should involve the best intensity when planets are well positionned so with a short time occurence.
However we cannot discard this hypothesis.

The fact that 0.001 cd/m2 is calculated with some optimistic hypothesis means a scotopic vision mode.
For instance Uranus with 360x in a 8" involves tenth of cd/m2 as the surfacic light intensity for comparison.
Even under a black sky this is unprobable to see such.
For venus the sky is not dark enough for.

Now getting more ocurences at evening conjunction this means also something as interpretation. There is no enough data collected by each observer. The collection of several episodic observers cannot be an enough basis for making conclusions.
Each observer must produce more data before and after conjunction for getting more pertinence for the conclusions.
Stanislas-Jean


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Re: Ashen Light - Redux new [Re: azure1961p]
      #5753987 - 03/24/13 01:27 PM

Personnally this was collected from 50mm until 305mm on the same moments.
Stanislas-Jean


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Re: Ashen Light - Redux new [Re: buddyjesus]
      #5754174 - 03/24/13 02:30 PM

Buddy it is always interesting to perform tests for supporting observations. Some autocontrol procedure brings a lot always, the occulting bar can be one.
The occulting bar inhibs the lateral inhibition effect brings by some as objection. Frankly this would be more acurate and more built for adding something here.
The only pertinent idea for the moment concerns the lightning hypothesis which is physical and seems to bring some accessible light level.
The ccd objection is also not enough as the data collected are so episodic sothat without enough pertinence.
I doubt still of a possibility to capture this lightning light level being 10 000x time less around than the crescent and timed seemly.
Stanislas-Jean


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Re: Ashen Light - Redux new [Re: stanislas-jean]
      #5754212 - 03/24/13 02:47 PM

Quote:

Personnally this was collected from 50mm until 305mm on the same moments.
Stanislas-Jean




I have every belief.

Pete


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Re: Ashen Light - Redux new [Re: azure1961p]
      #5754266 - 03/24/13 03:14 PM

The occulting bar inhibs the lateral inhibition effect also.
Stanislas-Jean


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Re: Ashen Light - Redux new [Re: azure1961p]
      #5754299 - 03/24/13 03:31 PM

Quote:

Its regrettable that such a thing might preoccupy observing time rather than something with a greater sense of progressive discovery.

Pete




Pete if you mean what I think you mean then I find you a little out of order here: are you telling others what they should be directing their efforts to? One of the joys of being an amateur is you can, if you want, observe what you pretty much like and even if others think you are illusion-prone or over-imaginative etc……..! This AL observing takes little time anyhow, especially given the infrequency of opportunity.

Speaking for myself: after over five decades I reckon I’ve paid my observing dues and without any delusion/pretext that I was doing great things for science – if somebody has found some use, fine, and if not – so what! The thing for me is at the telescope enjoying the challenge of practicing the disciplines of careful and critical observing as per those great observers of the past for my own satisfaction and reported in good faith: but usefulness – Ann-Fairy-Ann to me!

In any case I am dropping off this thread as I can see that circularity looms and have pretty much said my piece and presented my work and views in good faith.

Before signing up to CN I was pretty much anti-forum but I have quite enjoyed things here so far in the main. Tended to shun forums but our two sons monitor a few and alert me when my name crops up (Uranus thread); thus here I am! Though I have told them to drop their sensitivity meter a couple of notches! My doc tells me at 68 I have the constitution and blood pressure of a healthy 30 year-old and want to keep that way. I still retain, and protect, my sharp vision (1 in a 1000 an optician once told my mother) but Father Time could soon take that away so even more now I follow my own observing whims with apology to no one.

Now let us take a step back: with absolutely no disrespect to CN, we are performing on a relatively obscure platform; on the wider view of things are we all just shouting in the wilderness?

Edited by David Gray (03/24/13 04:04 PM)


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Re: Ashen Light - Redux new [Re: David Gray]
      #5754661 - 03/24/13 06:19 PM

Not at all. I was suggesting that in light of the evidence through satellites, computer aided telescopic vision that perhaps (the reason I used "might") there's something more productive to be had elsewhere. It's a discussion with both negative and positive feelings on this matter. I'm not out of order if my opinions don't jive with yours, its part of a gentleman's debate. You stated that you had a negative thoughts with regard to online forums prior to coming here. To be quite honest that statement in and of itself is a little off color in light of those folks who don't share that view.

First I was patronizing then Im out of order - in the same thread. I can't honestly sit here on eggs wondering which side of an insult Im in for.
And then if I don't well there's circularity in the air.

I think your preconceived notions on what you dislike about forums is an element that's resurfacing and its a pity. I think you re a great observer and artist ( patronizing forgive me).

Pete


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Re: Ashen Light - Redux new [Re: azure1961p]
      #5754735 - 03/24/13 06:55 PM

Reports of the so-called 'dark phase' of earthshine on the moon, and similarly for the AL on Venus, is further evidence of the power if illusion.

To recap, in the case of the moon, as the sky progresses from day to twilight, initially only the sunlit crescent is seen, then during a period the moon's night side is seen as a bit *darker* than the sky, thence transitioning to the earthshine appearing brighter than the sky.

To see the moon's night side as darker than the sky is quite impossible.

A particularly egregious representation of this is seen in the Vin Diesel movie, Pitch Black, when the rare eclipse commences and we see in the sky the silhouette of the ringed planet looming on the horizon. Dramatic, but quite unrealistic.

The intervening light of the sky always adds to the light of anything seen through it. Earthshine is a light source like any other. If this could be seen as darker than the sky when the sky itself is near to the same brightness, then any other object should also, when the brightness ratio between it and the sky is similar, be seen as darker. Such as, for example, a planetary nebula.

But not so. Such sources of light beyond the atmosphere are *always* brighter than the sky. Even a faint nebula in daytime is brighter than the sky. It's just that the brighter the sky relative to the object, the poorer the contrast.

I belabour the point only to show that some observers of the AL have seriously believed they saw the moon's and Venus' night side as brighter than the sky. Such a physical impossibility, having impressed itself nonetheless, surely must point to the possibility of the mind wanting to 'fill in' circular patterns with something.


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Re: Ashen Light - Redux new [Re: GlennLeDrew]
      #5754856 - 03/24/13 07:57 PM

I don't see either person being out of line except maybe when you both just got a little heated. Overall I think this thread has been much more civil than other similar ones in the past.

http://image.gsfc.nasa.gov/poetry/venus/V3.html Now to divert discussion. Would Venus having a very weak magnetic field make large auroral displays or prevent them? This is all I could find on the NASA site. http://pubs.giss.nasa.gov/abs/le06300n.html

I think we can all agree that Franz von Gruithuisen was wrong in thinking it was celebratory fires from the Venusian people.


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Re: Ashen Light - Redux new [Re: buddyjesus]
      #5754918 - 03/24/13 08:31 PM

notes on AL from this article

http://www-ssc.igpp.ucla.edu/personnel/russell/papers/ashen/

Ashen Light has been observed simultaneously and independently by 2 professional astronomers at least once /3/ and by up to 4 independent amateur observers on many occasions /4/. Ashen Light is thought to be an airglow or auroral phenomenon by some /2,5/, and airglow and aurora are seen from orbiting spacecraft /6,7/. In fact, the visible airglow at Venus is sufficient to saturate the Pioneer Venus star sensor when it looks directly at the planet /8/.

Only one optical observation has been reported, that of the spectrometer on Venera 9 which saw irregular optical pulses on October 26, 1975 at 1900 LT and 9o S latitude /1/. To our knowledge this is the only optical observation from orbit of the dusk hemisphere

this article also stated that the AL is reported to be one ten thousandth of the brightness of the lit side. Anyone better at log math than me able to figure out what the AL intensity reported is?


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Re: Ashen Light - Redux new [Re: buddyjesus]
      #5755061 - 03/24/13 09:55 PM

A brightness ratio of 10,000 between the day and night side is surely too small. That's a mere 10 magnitudes. This would be like having the -27m Sun lighting up one side and a -17m star lighting up the other hemisphere.

If that value is not a typo, it must refer to some non-visual spectral band...


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Re: Ashen Light - Redux new [Re: GlennLeDrew]
      #5755097 - 03/24/13 10:16 PM

they said ten to the minus four in comparison to the lit side, granted that canges based on the phase of the planet somewhat.

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Re: Ashen Light - Redux new [Re: buddyjesus]
      #5755465 - 03/25/13 03:12 AM

This ratio of 10 000 may involves on the planet dark side a light level that may be accessible visually.
A new time this depends on own eyes.
We have enough cd/m2 lighting surface to get this on paper.
If i remember well venus crescent is 5000cd/m2 that will involves around 0.5cd/m2 in average.
Specific conditions needs to be met pure sky, dawn light, nautical night sky. That's depends only on the eyes performance we have.
But the mystery remains for getting such light level from where!

Pete my blood pressure is 13.6-13.8 all the year, I can publish the bulletins with the venus AL report...
Stanislas-Jean


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buddyjesus
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Re: Ashen Light - Redux new [Re: stanislas-jean]
      #5755508 - 03/25/13 04:51 AM

i would like to learn from your report stanislas-jean. also looked up the next evening elongation and boy it doesn't look good this year for for northern hemisphere observers.

http://www.curtrenz.com/venus01.html


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Re: Ashen Light - Redux new [Re: buddyjesus]
      #5755519 - 03/25/13 05:13 AM

http://alpo-j.asahikawa-med.ac.jp/kk13/v130318r.pdf
You will find it here and all the data (drawings) on the same site.
The link was given at the beginning of the present forum.
Good read.
Stanislas-Jean


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David Gray
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Re: Ashen Light - Redux new [Re: azure1961p]
      #5755566 - 03/25/13 06:48 AM

Quote:

Not at all. I was suggesting that in light of the evidence through satellites, computer aided telescopic vision that perhaps (the reason I used "might") there's something more productive to be had elsewhere. It's a discussion with both negative and positive feelings on this matter. I'm not out of order if my opinions don't jive with yours, its part of a gentleman's debate. You stated that you had a negative thoughts with regard to online forums prior to coming here. To be quite honest that statement in and of itself is a little off color in light of those folks who don't share that view.

First I was patronizing then Im out of order - in the same thread. I can't honestly sit here on eggs wondering which side of an insult Im in for.
And then if I don't well there's circularity in the air.

I think your preconceived notions on what you dislike about forums is an element that's resurfacing and its a pity. I think you re a great observer and artist ( patronizing forgive me).

Pete




I think you take my post as more harsh than intended; I simply asked: “…are you telling [ok: might be] others what they should be directing their efforts to?” As well as stating my position as an amateur I was begging the question *What’s the harm in looking?*. Giving the rarity andthe logistics of AL checking opportunities diverting from my other ‘more useful’ observing pursuits was very minimal at most – we should not “walk away crying illusion, illusion” – earlier post.

I do not think I said/implied that you were out of order because our opinions don’t “jive”…. where did I say/imply that?? We can’t enter each other’s heads and see through each other’s eyes but some of the long-distance analysis (of observers and optics) that goes on at times starts to look as if some think they can. A well known palaeontologist once said “There’s too much explaining-away with dinosaurs……..” and likewise here I feel and as I indicated had my say.

Forums: not preconceived (!) – observed; but happy to find CN a cut above those that developed my cynicism.

In conclusion I honestly hope we can retain a friendly disagreement (don't worry about eggs!) and no offence intended! I am pretty much out of the thread simply for this reason: with little to add other than keep repeating in response to repeated contentions (circularity!) and all strength to its continuance whatever its outcome; and it needs to stay on course.


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Scanning4Comets
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Re: Ashen Light - Redux new [Re: azure1961p]
      #5755946 - 03/25/13 11:22 AM

I've seen it also!

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photonovore
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Re: Ashen Light - Redux new [Re: Scanning4Comets]
      #5757989 - 03/26/13 11:24 AM

In yet another thread elsewhere (http://cosmoquest.org/forum/archive/index.php/t-83338.html) the magnitude of Earth as seen from Venus was calculated by Kurt Rense as follows:
Quote:

If it were possible to stand on Venus and look at the Earth, how bright would the Earth shine? Would it be as bright as Venus appears to us?

As Veeger notes the absolute magnitude (100% illuminated at 1 AU) for Venus is -4.40 and -3.86 for Earth. As George implies the greater absolute brilliance of Venus is due to its nearness to the Sun and 100% cloud cover.

The visual magnitude of Venus varies from about -3.9 around superior conjunction to -4.7 at greatest brilliance. The latter occurs almost exactly midway between the dates of greatest elongation and inferior conjunction. Toward inferior conjunction the magnitude dims to a hugely positive value. At inferior conjunction Venus and Earth are separated by an average of 0.277 AU. As viewed from above the clouds of Venus, Earth would be in opposition to the Sun and 100% illuminated at magnitude -6.65 by my calculations. That’s about 6 times brighter than Venus at its greatest brilliance as seen from Earth.




Comparisons between the earthshine upon the Moon and earthshine upon Venus must include consideration of the
difference between lunar and Venusian albedo: 0.12 vs Venusian of 0.76 (bond) or 0.12 and 0.65 respectively, visual. Earth albedo varies (cloud cover seasons etc) from from norm within a 60% overall range. Also if Curt's calculations are correct (and from past experience i suspect they are or very close), the increased brightness vis a vis earth as seen from Venus vs. Venus as seen from earth--factor of ~6 (using _average_ albedo). A gibbous phase of earth as seen from Venus, which would be the case (decreasing) as Venus approaches inferior conjunction, would also have to be factored in, but i do not suspect it would make much difference in the overall earth brightness calculation...

Now the ability of Venusian light to cast visible *shadows* upon Earth is ample evidence that Venusian light reaches our planet in measurable and visible quantities. Conversely, that measurable levels of light from earth must reach the Venusian clouds, when the Earth is only at least as bright as Venus, (let alone six times brighter) seems a foregone conclusion to me.

The only question remaining for me is whether or not the eye is sensitive enough to detect that light upon the otherwise un-illuminated cloud deck of Venus from earth. The cd/m is a mathematical calculation whcih would result in a range based upon effective earth albedo and to a lesser extent phase (full, gibbous), distance between bodies... then add in the lesser lunar contribution, also variable dependent upon phase and varying albedo between far and near sides and distance (orbital location). *then* one would take that result and juxtapose it with the sensitivity range of the human eye--which is perhaps the least objectively defined parameter of all... I suspect any result will be ultimately "inconclusive", rendering only some range of probability rather than certainty as a "resolution". When one adds in possible but unquantified contributions of additional (light producing) atmospheric phenomenon from Venus itself, it would seem reasonably intuitive that Venusian ashen light is somewhat less likely to be wholly illusory than partially real.


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Re: Ashen Light - Redux new [Re: photonovore]
      #5758809 - 03/26/13 06:26 PM

Mardi,
The illumination level alone is not the only variable; so is contrast. In order to be seen, the ashen light would have to be no fainter than about four magnitudes below the brightness of the immediately surrounding sky (assuming glare from the sunlit crescent can be completely blocked.)

I've already outlined my reasoning which concludes that if the ashen light is from external sources, its surface brightness should be not too dissimilar from that of snow on a moonless night out in the country, which we may take to be about 21 magnitudes per square arcsecond. This tells us that the sky surface brightness should be no brighter than about 17 MPSAS.

At what solar elongations has the ashen light been observed? The nearer to the Sun, the more intense the zodiacal light. Even though the bulk of this light is behind Venus, it does provide a background of some brightness which reduces contrast. Indeed, I should think some small contribution to zodiacal light comes from *in front* of Venus, it being potentially important only due to the greater efficiency of forward scattering, in spite of the sma optical depth. This could then be another contrast-robbing element.

And of course there is the matter of our own atmosphere. At the required elongations for ashen light to be detectible, Venus is prone to lying not so far above the horizon when the sky is sufficiently dark. Natural airglow, and potentially residual twilight (it is in the direction of the Sun, after all) are additional sources of sky brightness.

Between the three sources (zodiacal light, airglow and twilight), It might well be difficult to have Venus in its crescent phase suspended against a sky darker than required.

In any event, it's most important to consider contrast, for after all the eye is fundamentally a contrast detector where image structure is concerned.


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azure1961p
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Re: Ashen Light - Redux new [Re: GlennLeDrew]
      #5759336 - 03/26/13 10:39 PM

Glenn a lot of nice points. Particularly the inability to ever get Venus at proper phase in a truly dark sky is food for thought. I'm cheating here by me running the ashen light phenomenon in the solar system imaging forum in the event anyone has ever imaged the night side. I think its thin and we all would've heard about it by now but for the sake of being thorough its there.

It would seem the atmospheric and solar system light scattering would never truly allow this ashen contrast to show but the exercise in thought modeling is intriguing and that's a good thing.

Pete


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Re: Ashen Light - Redux new [Re: azure1961p]
      #5759497 - 03/27/13 01:47 AM

All I see here is degrees of improbability, or of difficulty in attaining the required conditions for observation of the phenomenon. This is a *far* cry from being any sort of evidence of its nonexistance. It's a relatively rare observation, and probably requires extraordinary circumstances. Glenn is on the right track, I think, by asking during which elongations it's been seen. These are the sorts of questions that will bag the gold ring.
Also, a magnitude -6.65 Earth would, I think, cast a hell of a light on Venus. As a superior planet, Earth would be straight overhead at Venusian midnight at opposition. With an albedo of .76, it seems very possible that this reflection would be visible under the right conditions.

Confining one's efforts to coming up with reasons why these observations must be impossible, when they have, in fact, been made for centuries by many great observers, is self-defeating. There are no similar reports about Mercury; this should be a telling fact.

This, like many other telescopic phenomena that haven't been explained away by the age of spacecraft, seems to have made its way to the "oh, not that again" list of inconveniently persistant observations.


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Re: Ashen Light - Redux new [Re: Rick Woods]
      #5759553 - 03/27/13 04:01 AM

I think 4 magnitude difference between crescent and dark side is very conservative view. This can be beyond.
Imagine also long distance cible tests with the respective light levels, practive viewing on with occulting bar and not and set conclusions. This will be interresting to see.

Pete practice with the occulting bar the venus views. We never read from you about.

When we try to explain through calculations and "standard" eye properties, the conclusions will be long forums for no conclusion. Therefore the practice of tests will go for conclusions with your own eyes.
That's it.
The Venus mystery remains.
Except for space shuttles that reported this very faint and there is an hypothesis regarding lightning being the more pertinent. For the rest.
The long distance cible is easy to create: a square hole lighted behind with the right cd/m2, the dark side is covered by a panchromatic film of a known density for the simulation. The width of the lighted side can be variable.
That's save a lot of discussions. Just do it.
Stanislas-Jean


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GlennLeDrew
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Re: Ashen Light - Redux new [Re: stanislas-jean]
      #5759625 - 03/27/13 06:29 AM

Stanislas-Jean,
I fear you may have misinterpreted. My statement of a maximal 4 magnitude difference in surface brightness referred to that between Venus' night side and the *sky*, and most certainly NOT between Venus' night and day sides! In the latter case, the difference is more like 20 (!!!) magnitudes, or a factor of 100 million.

This is a most important factor which is all too easy to overlook. That such a subtle glow as the purported ashen light is reported in the presence of the blazing glare presented by the sunlit crescent must give one pause.

Let's break it down.

For the sake of argument, we'll accept the surface brightness of the sunlit and night sides as 1 and 21 MPSAS, respectively, for a difference of 20 magnitudes. Furthermore, we'll take a phase where the night side presents as 80% of the projected area of the disk. In other words, the night side has 4X the area of the day side. Considering the areal ratio and surface brightness, the day side has an integrated brightness 18.5 magnitudes, or or 25,000 times brighter than the integrated brightness of the night side.

Consider this carefully. Such a brilliant source immediately adjacent to another must compromise the visibility of the fainter, especially when the latter is already of low contrast with respect to the surrounding sky.

After all, observations of a magnitude 10 nebula of surface brightness 21 MPSAS is becoming hindered by the presence of a magnitude 2 star *anywhere* in the field, let alone immediately adjacent. If a star a mere 8 magnitudes brighter than the object of interest and some distance removed on the retina is becoming problematic, how deleterious must be a source of light 18.5 magnitudes brighter and immediately adjacent!?!

Again, the very brightness of the crescent imposes a severe constraint on the visibility of the ashen light. And that observations have seemingly been made with the Sun *above the horizon* suggests in the strongest terms an illusory phenomenon.

If earthshine is to be credited as the source of the ashen light, then it must absolutely be visible at every crescent phase of Venus. The variation in Earth's albedo is simply too small to render the phenomenon so ephemeral.

Finally, an unambiguous--even sketchy--photo is to be desired. That only visual observations (or am I mistaken?) seem to exist places this phenomenon in the realm of the perennially elusive UFO. As I've stated, imaging technology will not be at all pushed to any extreme in recording this light, if it exists.


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Re: Ashen Light - Redux new [Re: GlennLeDrew]
      #5759643 - 03/27/13 07:05 AM

Rick,

Mercury has several things going against it that preclude it from comparison. Its reflectivity is far lower than Venus, seeing is usually atrocious when observations are able to be made, the sky is never quite dark enough. In line with my doubts as to thus being a physical reality but eye/brain illusion I would also submit that the brilliance of the crescent is needed to *fill out* the ashen light effect. As far as I kno , besides difficult albedo markings the blunting of the southern cusp is one of the only things visible - that and its phases.

Pete


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Re: Ashen Light - Redux new [Re: GlennLeDrew]
      #5759706 - 03/27/13 08:08 AM

I feel you are making hypothesis wiith an overall view, crescent, dark side, backgroung sky.
A back ground sky of 18.5 is a good sky (with regards to SQM readings) and probably not a nautical sky where for venus this is the best condition possible.
Now the use of an occulting bar or side into an eyepiece, you see, make some objections. With the method described by me before, without the crescent presence AL is collected under different conditions of sky light levels.
And this is something under the ratio of 10000 between the cerscent and dark side, may be little less.
This was evaluated coarsly just by approach with the lond distance tests.
This is where I am to-day and my conclusion is that the level is not so confidential as galaxy light levels for which a scotopic vision will be involved and therefore unaccessible under the observationnal conditions we have because impossible. Light level to keep mesopic vision is requested.
Now regarding mercury i never saw some lights on the dark side and never reconstituted a pseudo circle of the dark side on the planet.
On venus the observations reported for the AL the dark side is not always a full lighted dark side, sometimes not sometimes yes with one or until 3 steps of light tones.
Please refer to the drawings issued on the japanese alpo site.
I donot pretend this an absolute true but this is reported under the conditions you know.
For ccd, because this is the only pertinent objection, what we have is:
- some few reports from space shuttles, noted in green light (lightnings)
- some ccd reports performed in NIR with 800-1000nm filters, with a light repartition, sometimes dark features collected,
- trials in visible light fields where above a certain exposure the dark side is quickly covered by the light glare, even with a side occulter.
And my question was how to improve the light glare disturbance inconvenience in order to perform clearer views?
Remind here also that past great observers reported seriously light levels on the venus dark side. It's not unfortunately a canali problem but just a light level problem to capture, not greatly confidential.
So the acurate method or imaging procedure in this way.
Whith the acurate method used and no obtained results this will answered, for the moment the mystery continue.
Stanislas-Jean


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Re: Ashen Light - Redux new [Re: stanislas-jean]
      #5760414 - 03/27/13 02:05 PM

For those interrested by the aurorae phenomena, something here
especially sheets 6 and 41;
http://hebergement-pdf.com/mypdf.php?n=412
This can be downloaded I presume.
Is this can involve the whole dark side this remains a discussion point.
I found this on a CN forum regarding Mars aurorae.
Stanislas-Jean


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Re: Ashen Light - Redux new [Re: stanislas-jean]
      #5760871 - 03/27/13 05:24 PM

It occurs to me that one way to explore the effect of large differences in surface brightness is by observing lunar craters near the terminator. Much of the crater floor will be in shadow, but the sunlit portion of the interior wall will illuminate the opposite interior wall that's in shadow. The effect will be much like earthshine, with the sunlit 'crescent' of the crater rim immediately adjacent to the partially lit but interior wall.

Depending on the crater depth, wall steepness and angle of sun, a range of conditions can be examined. For example, a steep (shadowed) crater wall facing a largely lit interior of the crater will receive a great amount of illumination. A crater for which only a tiny part of the far rim is sunlit will provide much dimmer illumination to its shadowed interior.

A large scope that provides sufficiently high power to frame a single crater but without having to use an excessively small exit pupil would be better, I think. And eyepieces having a small apparent field of view might be oreferred, making it easier to cut out more of the sunlit surface. With judicious framing so that a minimal amount of sunlit surface is in view, try to detect the illumination on the shadowed wall.

This should be a potentially easier observation than the ashen light. A well lit crater interior presents a quite significant solid angle of illumination as seen from a point partway up the shadowed interior wall. Picture the scene from an astronaut's point if view. A vista of sunlit surface more than 90 degrees wide and a couple or few degrees high is of order a couple hundred square degrees. That's MUCH more light than comes from the 2 degree diameter Earth.

The surface brightness of sunlit lunar soil at near full phase (as it is here, due to the scattering coming from very nearly opposite the Sun) is 3.5 magnitudes per square arcsecond. If we assume 200 square degrees as the extent of this source, that's 1/100 the area of the 20,000 square degrees comprising a hemisphere. Any point on the shadowed interior wall will have a surface brightness of about 0.01 * 0.11 that of the sunlit surface. The 0.01 is the fraction of the hemisphere providing light, and the 0.11 is the surface's albedo. And so the shadowed wall will be 0.0011 times as bright as the sunlit surface, which is 2.5 LOG(0.0011) = 7.4 magnitudes fainter, yielding a surface brightness of 3.5 + 7.4 = 10.9 magnitudes per square arcsecond. That's pretty bright! Neptune, at 9.4 MPSAS, is only 1.5 magnitudes, or 4X brighter. The brightest planetary nebulae have a surface brightness of 'only' 13-14 MPSAS.

The foregoing calculation probably gives an optimistically bright interior crater wall. The sloped surface will intercept the light from the opposite side less efficiently, and surface undulations and roughness must further decrease the mean brightness. The actual surface brightness must be a magnitude or more fainter. Nonetheless, a reasonably well lit crater wall in shadow is pretty bright in absolute terms.

At the eyepiece, if we allow some portion of the sunlit surface into the field of view so as to 'simulate' the glare from Venus' crescent, and we find it difficult to detect illumination on the shadowed crater wall, this would imply an even more difficult detection of the lower surface brightness night side on Venus.


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Re: Ashen Light - Redux new [Re: GlennLeDrew]
      #5761225 - 03/27/13 08:23 PM

This thread shows a very excellent example of Venus imaging in the hands if some talented people. As Id said before and now they say, if it exists it would've been imaged by now. At any rate some brilliant work here on that planet:

http://www.cloudynights.com/ubbthreads/showflat.php?Cat=0&Number=5761205&...

Pete


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Re: Ashen Light - Redux new [Re: azure1961p]
      #5761285 - 03/27/13 08:52 PM

Pete,
Thanks for pointing to that thread. It's good to have many heads contributing.

As to the distance over which Earthshine must propagate to Venus, it's not the distance so much as it is the tiny solid angle occupied by Earth as seen from Venus. In the General Forum I started a thread about surface brightness which outlines concepts relevant here. The math, while not at all complex, will cause some eyes to glaze over nonetheless, I'm sure.


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Re: Ashen Light - Redux new [Re: GlennLeDrew]
      #5761298 - 03/27/13 08:59 PM

Ill have a look thanks for the heads up.

Pete


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Re: Ashen Light - Redux new [Re: azure1961p]
      #5761714 - 03/28/13 03:10 AM

That'only images of the lighted phase of venus.
A new time nothing to see.
The challenge is to capture an hypothetic light level on the dark side.
With a ratio of 10000, 100000, etc... under a qualified method, not a click-clack exposure kodak is workung for you.
For the moment nobody answered this, in first you as usual.
Stanislas-Jean


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azure1961p
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Re: Ashen Light - Redux new [Re: stanislas-jean]
      #5761808 - 03/28/13 07:04 AM

No Stan it's you as usual dismissing facts because it isn't convenient to your posturing - if you had actually read the thread and followed the link its s little more conclusive than that. While it can be argued these are infact stills and a night time event could've occurred unbeknownst to the imagers this casual "click clack" swipe at some of the best imagers out there debases your own credibility. At least read the thread before you slam it.

Pete


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Re: Ashen Light - Redux new [Re: azure1961p]
      #5761892 - 03/28/13 08:11 AM

Is it a reference, surely not.
What is a qualified method for acquisition?
Stanislas-Jean


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azure1961p
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Re: Ashen Light - Redux new [Re: stanislas-jean]
      #5761960 - 03/28/13 09:14 AM

Some things can't be explained away with simple translator miscommunication and this one of them. Your question has already been addressed in the previous post.

If you are looking for a Kodak camera and one going click clack then this is all very pointless.

Pete


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Re: Ashen Light - Redux new [Re: azure1961p]
      #5762166 - 03/28/13 10:52 AM

I thought the photos were beautiful. I was surprised to see details in the images for the dark half at all. Not quite definitive but good data. Would be definitive I think if photos taken while others confirm that they see the AL taking place.

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Re: Ashen Light - Redux new [Re: azure1961p]
      #5762185 - 03/28/13 11:02 AM

Pete,
What Stanislas-Jean is getting at is that the images in that other thread are more optimized for the day side. In such case, the exposure will not properly pick up the much feebler glow of the night side and surrounding sky; these dim signals will be well lost in the noise. Longer exposures, which vastly blow out the day side into complete saturation. The images we've seen probably had typical exposures of order 1/100 second, whereas exposures of several seconds are required. In this way the much weaker signals can be brought well enough above the noise floor and measurements for any night side limb contrast undertaken.


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Re: Ashen Light - Redux new [Re: GlennLeDrew]
      #5762230 - 03/28/13 11:33 AM

Thanks Glenn.
The question is actually: what is a qualified procedure?
This a procedure that perform photometry assessments for the present case.
We try to determine the lights level that can involve a trace of the chipset: on the planet and in parallel on cible with known light levels.
Because the light level intensity is depending on the color channel and is disturbed by the light glare, mainly, the chipset has his own sensitivity to colour channels.
It's a problem regarding photometry measurements.
A kind of calibration method in fact. Had it been performed?
Answer is no.
Stanislas-Jean


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azure1961p
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Re: Ashen Light - Redux new [Re: stanislas-jean]
      #5762276 - 03/28/13 12:05 PM

John Boudreau hadentioned that exposures overexposing the Venus image still yielded no night side illumination and infact was the same black as the surrounding dark sky value.

My objection with Stan is his cavalier dismissal of the technology at hand and the talented individuals using it.

I'm a primarily visual observer. I dabble in imaging . I don't believe visual observing will ever fall out of favor as a rewarding pursuit . CCD is a great supportive tool to the endeavor.

Stan, the idea of the light level disturbing the chipset and other notions are unfounded. The diversionary contortions you go through to float a belief is astounding. These loopholes, conditional bypasses, faints, jukes and evasive maneuvering and what have you is beyond tedious.

Pete

Edited by azure1961p (03/28/13 01:14 PM)


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Re: Ashen Light - Redux new [Re: azure1961p]
      #5762497 - 03/28/13 02:23 PM

So we note.
But this is not a demonstration and a photometry measurement.
We donot know until which light level he was reaching on dark side (even with no result because this corresponding to a threeshold, not quantified and not calibrated).
Do you understand?
At final the light glare is a main disturbing point.
Perform trials you will see.
Do you remember forums for uranus and the no possibility of capturing the banding system: go to my report about, a below forum here you will have images about since july 2012 visual channels, OK.
Stanislas-Jean


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Re: Ashen Light - Redux new [Re: stanislas-jean]
      #5762621 - 03/28/13 03:48 PM

Ok here's where I opt out of the thread.

Cheers.

Pete


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Re: Ashen Light - Redux new [Re: azure1961p]
      #5763032 - 03/28/13 07:29 PM

One need not necessarily calibrate. The first task is to attempt to detect the night side's limb. For then even if the glare from the day side is strong, hopefully there is still sufficient contrast to trace the circular edge of the night side. If at least some segment of the dark limb is detected, and it lies where expected (as the continuation of the day side limb), one has made a pretty firm observation.

Taking into account, of course, a flipped ghost reflection of the sunlit crescent which by chance could line up very closely with the dark limb.

Naturally, all measures to block or attenuate the glare of the sunlit crescent can only help. Veiling glare can seriously reduce contrast. In any event, the exposure time must be sufficient to bring the sky glow at least a few sigma above instrumental noise, so as to afford a reasonable signal for the detection of the dark limb's edge.


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Re: Ashen Light - Redux new [Re: GlennLeDrew]
      #5763196 - 03/28/13 09:11 PM

There's always the possibility that the phenomenon was simply not occurring at the time the images were taken. Remember, it's only seen occasionally.

This is the same beef I have with the Martian Blue Clearing: no definitive observations are ever made at the same time the clearing is being reported telescopically. No HST, orbiter, etc. data is gathered to compare notes and try to solve the problem. It's strange; amateur observations are used frequently to support and supplement space probe observations; but the reverse never occurs. When an amateur observation could really use the input from a space-based observation location, it's never made available.


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Re: Ashen Light - Redux new [Re: Rick Woods]
      #5763352 - 03/28/13 10:50 PM

Has anyone compiled data in order to obtain some estimate of the ashen light's frequency? The lower the frequency, the more likely it must be due to some 'uncommon' phenomenon.

For example, if light reflected from Earth were to be the source, it must be seen at every apparition within some range of phase angle and when the planet is seen in a sufficiently dark sky. The range of brightness of Earth as seen from Venus, within the required range of phase angle, cannot be so large as to result in the AL 'switching' between readily seen and not seen. After all, Earthshine on the Moon at given phase varies not enough from one apparition to another to be at all apparent with any certainty. I should think Earth's albedo, considering extremes for the range of cloud/snow cover, varies by perhaps 50%, or 0.5 magnitude. Even a factor of two variance is 0.75 magnitude. This is not terribly significant.

If the observations of the AL are not sufficiently consistent in frequency when conditions would otherwise be favorable, I think it fairly safe to discount Earthshine as the cause of the AL. From nothing more than a statistical analysis, let alone the not inconsiderable faintness of Earthlight at Venus, and the difficulties imposed by considerations of contrast.

So, what other conceivable phenomena can cause a visibly detectable glow (necessarily at least in part within the visual spectral band), the surface brightness of which must compete with the dazzling sunlit crescent and other wreckers of contrast?


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Re: Ashen Light - Redux new [Re: GlennLeDrew]
      #5763503 - 03/29/13 01:15 AM

I would like to see the imagers try to block out the lit side some. couldn't hurt. Am I the only one who saw the dark side on some of the photos? even surface detail from the IR? That should be proof of the dark side images coming out with something, even if not AL.

i also agree, the phenomenon might not have been active during those photos. Considering there are AP people who do constant dark side moon monitoring for impacts, it wouldn't take much for someone to do an actual monitoring program with a webcam at least. Actually it would probably take two imagers at different sites to catch something simultaneously for definitive positive proof.


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Re: Ashen Light - Redux new [Re: buddyjesus]
      #5763585 - 03/29/13 03:10 AM

That's not enough but in the good way.
I insist that for making pertinent comparison photometry calibration is needed.
Because if the results on dark are negative, this means only the fact that a certain amount of light cannnot be and never be captured. A little above this value a certain trace on the image may commence to appear. From an observer to another, this light level, a threeshold, is not the same, not for a few but greatly (can go up 100x).
This threeshold well determined is an excellent indicator because we know where we are, even with negative results.
The AL if existing may be just under this level, this is a possibility.
According to long distance test the ratio of 100000 (near to for crescent/dark side)) remains visually accessible (this imply more or less a light level of 0.05cd/m2 on dark side).
Now with a 098BL chipset the exposure needs to be great sothat it is difficult to catch consistently something but we are not so far from this target.
So a step more in possibility is to be find. I am in a ratio of 10-100 of uncertainty between visual ability and imaging ability. The distance between the 2 means that I tried to evaluate. This is not accurate but a trial to fix the status, with a luxmeter how it is and the test method in use.

For the collection of AL data since decades, I know the BAA that does this job, Alpo may does also. The problem is the episodic collection of observations for each observer. Is the collection of several observers of unequal ability and conditions can do a representative status? This may be under question. Pesonally I didn't see all these data for having an accurate view about.

Buddy, you say you have data with light collection on the dark side. I am interrested in.
Could issue some of them here with the conditions in use?
This would be interrested to see for the discussion.
Stanislas-Jean


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Re: Ashen Light - Redux new [Re: stanislas-jean]
      #5763598 - 03/29/13 03:41 AM

http://www.cloudynights.com/ubbthreads/showflat.php/Cat/0/Number/5758956/page...

i clicked every link that was put up so it is in this thread or one mentioned.


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Re: Ashen Light - Redux new [Re: buddyjesus]
      #5763617 - 03/29/13 04:19 AM

Thanks Buddy.
In fact I saw these posts in past.
I noted the fact that in the range of 850-1000nm the images captured corresponded to deep clouds of the venusian atmosphere.
Most of the pictures given are for the crescent and some performed in NIR with 2 filters the 1000nm and the omega 956nm. The omega filter get clearer views with around 1s exposure more or less at F10.
I think the exposure pushed 10 or 100x more may occult the images even with the occulting bar in deep red channel. Now the observer may comment his work about, more than me.
These works pre-suppose the fact that nothing is existing in visual fields and this is not demonstrated in fact through these results for the reasons given in the last post.
AL may not exist but here this is not completed enough.
Matter of light levels expected to be catched.
Stanislas-Jean


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Re: Ashen Light - Redux new [Re: stanislas-jean]
      #5765055 - 03/29/13 03:45 PM Attachment (6 downloads)

this one from wayneJ is the one i saw the unlit side. it is in the thread I posted above. my imagination?

Edited by buddyjesus (03/29/13 06:17 PM)


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Re: Ashen Light - Redux new [Re: buddyjesus]
      #5765427 - 03/29/13 06:01 PM

Quote:

this one from wayneJ is the one i saw the unlit side. it is in the thread I posted above. my imagination?




That's correct.

Pete


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Re: Ashen Light - Redux new [Re: azure1961p]
      #5765478 - 03/29/13 06:20 PM

when i cover the bright portion, the dark side does darken(prolly to a moot level)but was still easily visible in the image to myself and bro. my guess is this was from the IR portion, but just guessing.

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Re: Ashen Light - Redux new [Re: buddyjesus]
      #5765754 - 03/29/13 09:20 PM

Ah correction to my affirmation - it is showing after all!. I'd guess the wavelength is responsible. Wayne would have the info on that as Im sure John B or Sean W might.

Pete


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Re: Ashen Light - Redux new [Re: azure1961p]
      #5766072 - 03/30/13 02:30 AM

It's quite common for a planetary imager to blacken a final result's background to a blackpoint of 0 in software. This is usually done in PhotoShop by either making a selection mask of the planet with a copy of the image, or since some planets like Venus are essentially round, by simply drawing a circular mask around the planet's limb. Then the sky background is converted to a level of 0 without effecting the planet's disk itself.

I've attached a strongly stretched version of Wayne Jaescke's image.

***Edit on 4/1: Note that I've deleted that stretched version of Wayne's image since it has served it's purpose as my analysis has been supported by Wayne himself in a follow-up post.

In this case, it appears Wayne had square-cropped the full RGB frames earlier as the dark part of the disk has a straight slice cut off vertically along the RH side. Then it appears that he used a circular mask to separate the background before dropping the blackpoint there. What you see as weak light on the dark side is background noise that had been included in the circular mask used to protect the planet. There is some darkened separation along the terminator that had to be done with a phase-shaped selection mask which puzzles me, but perhaps this was simply pasted over a circular-mask selection version he had done earlier. I'll drop him a PM and see if he recalls.

A couple of reasons for doing this include simply making a clean, black background for text in versions used in ALPO/BAA reports. Or because even keeping a very dark, noisy background would unnecessarily add to file size vs. a 0-blackpoint darkened background. Some guys use a sharp edged mask, others feather the edges a few pixels to blend the mask smoothly between planet and background. The result is then centered/pasted into a black frame used for presentation.

I usually blend the mask a few pixels and darken to 0, but in some cases it's best to leave the real background alone if it tells a tale itself. I always save early steps in processing with the noisy sky background if it's needed for review, BTW. My 1-micron thermal image GIF of the darkside of Venus on two nights linked earlier in this thread is one such image left that way even in the final result to show the glare/reflection pattern and a background star in one of the frames--- the same thing should be done with any serious Ashen Light imaging attempts too. Another example is a near-IR image of Uranus where the background demonstrates an accurate orientation of the planet by way of the position of a couple of moons--- that background was actually enhanced because the moons were not detected at the processing settings used for Uranus itself. In other words, I did use a mask for that image but brightened the background instead of darkening it.

http://alpo-j.asahikawa-med.ac.jp/kk12/v120524a1.gif

http://alpo-j.asahikawa-med.ac.jp/kk12/u120917b1.jpg

Edited by John Boudreau (04/01/13 08:30 AM)


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Re: Ashen Light - Redux new [Re: John Boudreau]
      #5766090 - 03/30/13 02:52 AM

John,

Those are reasons I don't believe imaging can be accepted as the final word in these matters; it's too influenced by the methods used by the imager to produce the final product. A little creative processing can erase many important features, if one isn't being strictly objective (as you obviously are), in order to create a more impressive image.

As an aside, I can't help notice how closely your image of Uranus agrees with the sketches Stanislaus-Jean has been posting.


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Re: Ashen Light - Redux new [Re: Rick Woods]
      #5766099 - 03/30/13 03:02 AM

very interesting. i learned a lot. Like I shouldn't look into AP cause it is too technical for me. haha. In all seriousness though, thanks for explaining what I saw in the image for me.

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Re: Ashen Light - Redux new [Re: buddyjesus]
      #5766145 - 03/30/13 04:23 AM

The question through this kind of method used for imaging remains
This suppose if the m10 star revealed on the venus picture that the stretching is still linear in order to keep the same scaling on the planet.
Are we sure of this?
If this is the method is a serious assessment.
Anyway at final through the manipulations, it would be interresting to test with the chipset to which light level it can be reached some light with the same exposure conditions and scope. To see by a parallel assessment the pertinence.
Stanislas-Jean


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Re: Ashen Light - Redux new [Re: stanislas-jean]
      #5766283 - 03/30/13 08:18 AM

Rick, an image presented as a "pretty picture" result is just that,massaged to produce the most visually appealing result. However, imagers should be both keeping their raw, unadulterated data and their notes for important observations such as these for actual scientific analysis. Pulling an image from a forum and manipulating it to bring out "hidden detail" is asking for trouble. This is exactly what bigfoot hunters and UFO believers do, which compounds the problem rather than reveals any hidden secrets.

Back to the question at hand, I've posted my results from my imaging campaign last year trying to detect the rumored ashen light in images. I had negative results, but should note the evening posted (5/18/2012) I had recieved an alert on an Ashen Light sighting, and amazingly it was clear here in NH. I observed the planet visually both before and after shooting through the scope, so I was not surprised at all to record nothing surprising that evening. I know it's not going to convince the believers, but it certainly convinced me. Additionally, I have spent 5 years studying Venus both photographically and visually. I have myself seen some interesting optical illusions which I describe in the other thread in the imaging forum, which only reinforced my skepticism.

Finally, there is just no way that the phenomena, if it exists, can't be photographed: John's and Christophe's images of the thermal emissions from the surface of Venus clearly demonstrate that although the illuminated crescent does create reflections and artifiacts, it does not obliterate the signal from the unilluminated side. So I still believe that if the phenomena exists, it can be photographed. But I'll leave that to others, as I made three concentrated attempts under excellent conditions, in a favorable apparition.


Edited by swalker (03/30/13 08:36 AM)


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Re: Ashen Light - Redux new [Re: stanislas-jean]
      #5766533 - 03/30/13 11:13 AM

Personnally on the 18th May 2012 the weather was not favorable here, but reported on the 13th.
Anyway, I am also convinced that if AL exists this could be captured by imaging and not shall be.
This is the only method that can do in this way.
However beyond the fact that the treatment may be linear, stretched, etc... I object the fact that we donot know where we are about the light levels in terms on number of cd/m2.
It is mandatory to know this because we will continue to speculate about.
We have to perform a comparison between visual and ccd capture methods that are not quite similar it seems (one for UFO and one for blind, sorry for the imagers from my opinion pertinent).
Otherwise I am conducting to think that even the 3°K fossil light of the universe will not exist because with 3sec of exposure at F24 and with the scope X it is not captured.
Light level: how many cd/m2 or any other unit?
Answer is O?: this is wrong because with light reflexion by planets to venus dark side, this is producing a light level not at O level (something as rather the mili lux level). Discussion at the beginning of the forum and Mardi's proposal. This should be on the chipset and this is not.
Stanislas-Jean


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Re: Ashen Light - Redux new [Re: stanislas-jean]
      #5766641 - 03/30/13 11:46 AM

It's not my problem to educate you on the functionality of digital cameras or myriad data analysis techniques, nor decipher your poorly translated posts.
I'm not claiming that I closed the book on the phenomena, just that I have satisfied myself with my attempts at capturing it.


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Re: Ashen Light - Redux new [Re: swalker]
      #5766765 - 03/30/13 12:16 PM

You satisfied yourself very well, however some quantified assessment remains welcome.
John get views with a m10 star not far to the planet sothat we have comparison elements in order to evaluate a certain light level on the dark side, in the wavelength reported.
From your results we remain blind and stetched linearly.
Stanislas-Jean


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Re: Ashen Light - Redux new [Re: stanislas-jean]
      #5766830 - 03/30/13 12:58 PM

OK, let's be civil, you guys. I don't want this thread getting shut down just when some interesting people are weighing in. There's nothing personal in this topic, and no need for anyone to be sarcastic. We all want the same thing; to figure out what's going on.

If the AL is an illusion, why has it been seen by so many first-rate observers over the years - people who know all about optical illusions? If illusion, what is its nature? If real, and it can't be/hasn't been imaged, why not? And, is anyone actually sure it hasn't ever been imaged?

Also: is everyone talking about the same thing as Ashen Light? I've variously seen the phenomenon described as the continuation of the cusp all the way around Venus; lighter reddish-brown markings appearing in the unlit hemisphere; now, someone referred to a darkening of the unlit side. What's the absolute definition of Ashen Light?


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Re: Ashen Light - Redux new [Re: Rick Woods]
      #5766868 - 03/30/13 01:19 PM

This will be kept honestly, Rick.
What I cannot admit is the fact that according the Mardi' proposal (reflexion of light by planet atmospheres on the venus dark side), the light amount created should be revealed by ccd with the procedures given through the previous posts.
And this is not on visual wavelength.
As a consequence I am wandering of which light levels the ccd procedures in use can reach (the 3°K fossil light of the universe?).
Photometry is not a concern, it is, quantified.
This is the node.
Stanislas_Jean


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Re: Ashen Light - Redux new [Re: stanislas-jean]
      #5766995 - 03/30/13 02:45 PM

I just wanted to chime in on the image of mine that was posted earlier in this thread. John was completely accurate in his analysis of the processing, but I also wanted to add that the image was taken in daylight, so the background of the UV channel was much brighter than that of the IR channel. The background was cropped for aesthetics. Anyone wishing to analyze any of my data for scientific purposes should let me know.

That said, there was no visible-light component to that image -- it's a UV(G)IR image made through an Astrodon UVenus filter and Astronomik Pro Planet 805nm filter -- thus there is no value in analyzing it with regard to the Ashen Light phenomena.

With regard to the AL phenomena, I've been an observer for nearly 40 years and have never seen it, despite many visual and photographic efforts to capture it. I will, however, remind my fellow visual observers that there are those who will swear that they've seen bigfoot, UFOs, and a second-shooter on the grassy knoll. As the old saying goes, extraordinary claims require extraordinary proof. As the AL phenomena continues to elude photographic proof, despite consistent and rapid advancement in imaging technology, makes the claim of the AL as a real phenomena that much more 'extraordinary' in my opinion. Further, given that numerous space based probes have failed to locate any phenomena that supports the 'legend' of the AL makes visual observation claims of this phenomena more extraordinary.

Regards,

Wayne


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Re: Ashen Light - Redux new [Re: WayneJ]
      #5767034 - 03/30/13 03:05 PM

Yes Mr Wayne I read you with interest.
CCD results are a pertinent objection to AL light existence.
But, regarding the light level created by the light reflexion of solar light from solar planets (earth moon,...) on the venus dark side can be calculated to an amount that is true and existing (some evaluated to be 0.001cd/m2 around).
So why this is not recorded by CCD?
This is the objection.
Where this is wrong?
Stanislas-Jean


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Re: Ashen Light - Redux new [Re: Rick Woods]
      #5767173 - 03/30/13 05:03 PM


Rick,

I think it goes to prove (perhaps) that even knowledge and understanding of an optical illusion isn't enough to disolve or prevent its recurrence but just reconciliation in the nature of the phenomenon. I can literally produce an ashen-lite-like illusion even though I kno its false. I've seen it in nature manmade and natural. My assertion is its the eye/brain filling in on the suggestion of a shape or pattern.

While its unfortunate a select few greet the finds of the three imagers like so much garlic for Dracula, I think its a liberating tool for visual observers.
It can help define boundaries while also opening potential challenges for observing projects and programs simply because by virtue of the information rich results. I'm convinced if there were less resistance to technology by some dyed in the wool visual observers (of which Im one) the debate would be more productive. When the arguments against CCD as a tool bog down in tedious evasive writhings it becomes posture over substance and it debases validity.

Rick Ive enjoyed the thread for the greater part. That these fellas weighed in was appreciated. I'm glad you redux'd even if Im still wanting in terms of evidence.

Pete


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Re: Ashen Light - Redux new [Re: azure1961p]
      #5767671 - 03/30/13 09:36 PM

I would like for it to stay civil also. This thread has been the most civil in regards to an controversial phenomenon as I have seen on CN.

WayneJ, sorry for posting without your permission. I figured it would be cool but wasn't sure as it was noncommercial/educational use and credit was given. If the mods or you wish to remove feel free. I didn't know how to link to just his post and not the top of the thread. Please excuse my ignorance.

now I don't know imaging, but I have a question just out of curiosity as I feel it pertinent to add to the continued discussion. Would the background noise be eliminated with a dark balance or a white balance? Thanks for any input.


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Re: Ashen Light - Redux new [Re: azure1961p]
      #5767692 - 03/30/13 09:47 PM

Regarding attempts at imaging.

Perhaps one way to at least mitigate against the great glare from the sunlit crescent is to, in quick succession, obtain images of identical duration with and without Venus in the FOV. By this measure, one should have an 'uncontaminated' base image of the sky glow, which could be used as a reference for subtraction of the glare.

Note, I'm just blue-skying here; I'm not sure if such an approach would be viable. And if it is, even with the use of an occulting device such technique might still be worth doing, for there will still be scatter of the bright Venusian light as it transits the optical system, introducing veiling glare of some extent.

All to provide the best case scenario for the detection of the ashen light.

This notwithstanding, I feel that if the ashen light is real, and visible to the eye in spite of the glare if the sunlit crescent, then it *must* be recordable without having to go to extraordinary lengths or employ near wizardry. After all, the camera is no worse affected by glare than is the eye. And it's so easy to stretch and process an image to bring out subtle features, without introducing spurious, doubt-inducing artifacts. As long as the exposure is sufficient to bring the sky glow well enough above the level of instrumental noise.

This is not difficult to achieve, for the sky will be no darker than about 19 magnitudes per square arcsecond. And so an exposure of around the half-minute range should suffice, unless the f/ratio is rather large. Here is where a large aperture helps; it provides good image scale at a faster f/ratio.

Unlike Stanislas-Jean's concerns, if detection is the aim, it's not necessary to know what the illumination level is. Even if of extraordinary faintness, it must perforce be a little brighter than sky glow, for the light of the sky always adds to the light of the object seen through it. The only concern is maximizing contrast transfer so as to have a hope of detection if the AL is intrinsically fainter than sky glow by more than about 4-5 magnitudes. (For example, if fainter than the sky by 5 magnitudes, it is 1/100 as bright, and so this feeble light, when added to the foreground sky glow, makes for a source 1% brighter than the sky; pretty low contrast.)


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Re: Ashen Light - Redux new [Re: GlennLeDrew]
      #5767837 - 03/30/13 11:11 PM

Quote:

WayneJ, sorry for posting without your permission. I figured it would be cool but wasn't sure as it was noncommercial/educational use and credit was given. If the mods or you wish to remove feel free. I didn't know how to link to just his post and not the top of the thread. Please excuse my ignorance.




I have no objections to the manner in which you used my image It's fully consistent with the Creative Commons use-license that I have on my website.


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Re: Ashen Light - Redux new [Re: WayneJ]
      #5767883 - 03/30/13 11:33 PM

that is what I thought. thanks

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Re: Ashen Light - Redux new [Re: GlennLeDrew]
      #5768048 - 03/31/13 03:28 AM

I read all the posts emitted during night.
I recognise that the ccd procedures constitute a step more for an explanation.
However, may I insist on the fact of the, you remember Glenn of the assessment regarding lighting created by light planet reflexions), such AL must be collected by the procedure explained. This is creating a sufficient light level because John showed a M10 magnitude star (in NIR), why not in white light, an others nothing in other light fields, against the backgound sky of m18 as you wrote.
This kind of AL light must be recordable in white light because the amount of light is sure and existing, not hypothetic, , not accessible to eye, and, evaluated to be around 0.001cd/m2.
The 2 way approaches cannot be crossed for making something convergent for the moment.
Stanislas-Jean


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Re: Ashen Light - Redux new [Re: WayneJ]
      #5768795 - 03/31/13 01:24 PM

Quote:

Quote:

WayneJ, sorry for posting without your permission. I figured it would be cool but wasn't sure as it was noncommercial/educational use and credit was given. If the mods or you wish to remove feel free. I didn't know how to link to just his post and not the top of the thread. Please excuse my ignorance.




I have no objections to the manner in which you used my image It's fully consistent with the Creative Commons use-license that I have on my website.




If you want to post a link to a photo on CN, look at the box immediately below where you are typing your post. You will see a box entitled "Instant UBB Code. In that box click on the 'URL' link. A dialog box will appear. Paste the URLof the picture there and press ok. Another dialog box will appear where you can type something like 'Wayne's Venus Pic' and press ok again. Now your link will appear in your post in underlined green saying "Wayne's Venus Pic" instead of a hundreds of characters long, ugly URL.

Easy once you've done it a couple of times.

Wayne, you were most kind to give permission after the fact but our TOS trumps that. To post a pic not your own, post a link. Saves difficulties that did not arise here but can and have happened on CN in the past.

As you were,

Dave


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swalker
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Re: Ashen Light - Redux new [Re: Cotts]
      #5770315 - 04/01/13 09:20 AM

This is an interesting discussion, though admittedly frustrating. Stanislas-Jean, one can easily determine the background sky brightness from my original data not by recording a star (which all but the brightest were invisible at the time I shot- the Sun was still up), but simply calculating the mean value of the background signal in the test exposures I conducted on images with no planet or other subjects in the field using the same exposures that evening immediately preceding my images. Also, comparing John's near-infrared image that serendipitously captured a star in the field is folly: in near-infrared light, one can detect many stars in broad daylight. Indeed, many objects are more visible in near-infrared light during the day. In January of 2007, I recorded comet McNaught as it was cosest to the Sun using the same technique as John. But star brightness values in near-infrared light rarely if ever correspond to the visual magnitude estimates published in star charts for two obvious reasons: near infrared light is invisible to the human eye, and many stars are far brighter in wavelengths beyond the range of human vision.

That said, many of the historical sightings of ashen light were seen in broad daylight, particularly Dale Cruikshank's memorable observation by a similar-sized telescope (12-inch Newtonian)in 1962. My campaign was meant to duplicate what I felt was the most credible sighting in recent history.

I have not posted even deeper exposures I took through un-filtered light that night, where the over-exposed region of the planet bleeds much more into the planet's un-illuminated region (recorded at 3.75 frames per second using the same camera and setup, gain at 0) because they also show nothing.

Again, I state that I visually observed the planet both before and after my images, and continued to observe as the sky darkened. But because I failed to detect any sign of a glow as twilight deepened, I determined that further imaging would prove fruitless on each of the three nights.

To answer an earlier question, I believe the term "ashen light" refers to the sighting of a faint glow within the disk of the planet, not simply the extended or even connected "cusps" of the back-illuminated atmosphere.

I continue to remain skeptical of all ashen light sightings. Perhaps I'll try again in the next favorable elongation from my latitude; it really does not take much more additional time or effort when trying to capture "pretty" images on the same nights.


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stanislas-jean
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Re: Ashen Light - Redux new [Re: swalker]
      #5770722 - 04/01/13 12:33 PM

Frankly I read all the posts here and yours.
I am on the way to be convinced for recognising this ccd procedure as a serious objection to AL light existence.
However for an effective completeness of the subject, I feel it is necessary to trace and define the "ends", the cursors of the procedure in term of light levels corresponding to.
The m10 star on John picture is interresting for me because we have a known reference. Well, this is in NIR field but there is a reference. It's important to have a reference in order to compare the lighted part intensity of the dark side. With this, the collected light intensity level seems to be 7th_8th magnitude level in NIR on dark side: an important data that can be extrapolated to other light fields taking into account hypothésis (the origin of the phenomena).
Mr Cruikshank's results are here in my files about this subject as also some those from BAA( Mr Baum, etc...).
I never saw this AL light on the 80ies (was Alpo member), just this last conjunction 2012.
Stanislas-Jean


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swalker
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Re: Ashen Light - Redux new [Re: stanislas-jean]
      #5770791 - 04/01/13 01:07 PM

If Cloudy nights were a peer-reviewed journal then I'd be obligated to present such work.
But the fact of the matter is, I didn't measure it, I gave up on completing the analysis of the data because it still proves nothing except there was no ashen light display that night, nor on the 13th, or even the 3rd of that month. But I'm sure you just can't resist having the final word in the matter, so fire away.


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GlennLeDrew
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Re: Ashen Light - Redux new [Re: swalker]
      #5770974 - 04/01/13 02:46 PM

A star is not necessarily a good fiducial, or reference in cases like this because we are concerned with a surface of low contrast whose brightness is considerably impacted by the superimposed glow of the atmosphere through which it is seen. The sky glow must be subtracted in order to determine the intrinsic surface brightness.

Merely looking at an image containing this 10m star and extrapolating to a night side surface brightness of 7-8m (what units; integrated light or magnitudes per square arcsecond or arcminute?) is likely to be significantly in error.

And besides, the near IR night glow is not visible to the eye and hence is meaningless in the context of the visual sightings.


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Rick Woods
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Re: Ashen Light - Redux new [Re: swalker]
      #5771149 - 04/01/13 04:35 PM

Quote:

I continue to remain skeptical of all ashen light sightings. Perhaps I'll try again in the next favorable elongation from my latitude; it really does not take much more additional time or effort when trying to capture "pretty" images on the same nights.




Sean,
That's the best possible attitude; skepticism, but with an open mind. Something amazing might just turn up.

I can't help wondering, though, if the eye has capabilities that just don't exist with imaging devices. Combinations of abilities, with the brain to instantly draw conclusions, etc etc. I constantly find that pictures I took of wonderful, breathtaking landscape vistas become, when downloaded to my laptop, boring, plain pictures. Much of this is just that I suck as a photographer; but it's also true that pictures just can't capture the real view like the eye/brain combination can.


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swalker
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Re: Ashen Light - Redux new [Re: Rick Woods]
      #5771273 - 04/01/13 05:18 PM

Thats called non-linear interpetation Rick, which is what the eye/brain combination does quite well. CCD's and other digital detectors don't do it within one image, which is why there's non-linear stretching of data that occurs in image processing, and high-dynamic range (HDR) imaging that is popular in photography today. But does that mean a camera can't mimic what the eye/brain combination does? No. It just requires a different approach.

Note the use of the word mimic. Does a camera do what the brain/eye combination does? No it doesn't. But it can DETECT anything that can be seen visually. It might not make a pretty picture though.

The only way this will be settled is if an imager is on hand when a sighting definitively occurs. And thus far, none have.


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GlennLeDrew
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Re: Ashen Light - Redux new [Re: swalker]
      #5771312 - 04/01/13 05:37 PM

Within any given range of brightness, an image can bring out subtle contrasts that the eye simply cannot. Visually, it's difficult to differentiate contrasts below about 6%, or about 0.06 magnitude. A 16-bit camera can, in a single frame, distinguish brightness differences to around 0.02 magnitude. If areas are integrated across some thousands of pixels, or if noise reduction techniques are employed, discrimination to 0.01 magnitude is possible. And with judicious stretching, yet subtler differences can be brought out.

My figures can likely be corrected, as they may be applicable in cases where measurements are to be of a reasonable confidence level. To merely *detect* relaxes tolerances somewhat, certainly when integrating over an area, where the effect of instrumental noise is less injurious. But in any event, a camera can easily best the eye where the detection of subtle brightness differences is concerned. Proper technique and reasonable care will assure this.


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Rick Woods
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Re: Ashen Light - Redux new [Re: GlennLeDrew]
      #5771835 - 04/01/13 10:14 PM

This thread has inspired me! I've found a number of papers on the subject on the NASA-SAO-ADS website which I've downloaded and will be reading. I notice that the only mention of the Ashen Light is in the older books; newer ones don't mention it at all, not even to dismiss it. Older books treat it in great detail, generally conceding that it's a real phenomenon. This reinforces my suspicion that the AL, like the Blue Clearing, just isn't fashionable anymore in the face of so much more current (but unrelated) data.

The NASA Technical Report Server is down right now, under review to make sure nothing secret is being leaked to the commies/terrorists/aliens. I'll check it too, when it comes back up.


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buddyjesus
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Re: Ashen Light - Redux new [Re: Rick Woods]
      #5771947 - 04/01/13 11:16 PM

haha. share your findings!

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stanislas-jean
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Re: Ashen Light - Redux new [Re: GlennLeDrew]
      #5772107 - 04/02/13 02:40 AM

I know that the comparison between a m star and a sensible surface cannot be done directly. But this is what we have.
This is not a matter of personnal resistance but what I think is: we know now the ccd procedure in use and its powerful, what I am adding is the fact that a second method and may be a third one by other ways will get some results that can be crosschecked with the ccd procedure.
Some references needs to be introduced in order to calibrate some data. The 0 level is corresponding to what, I cannot imagine a 0 physical. Photometry may have some strange assessments. So the problem is to crosscheck with results got by other ways or methods.
Glenn, going to 6% only for human ability to make differences in terms of contrasts is not correct.
That's depend too to an observer and I can tell this is possible to go down substantially (see Uranus observations).
Blue clearing may not exist. But I am wandering why it was said by japaneese people that the phenomena (not can be) is the result of the ground properties in blue channel at the time of observation. Very well we are waiting the works results still having conducting to such assessment and status.
We cannot say this is without data coming from measurements and from only qualitative observations.
For me
AL is almost dead but completeness is still not achieved,
Blue clearing still on assessment, not supported by data results,
6% on contrast limit ability wrong.
Not opinions but observations and measurements.
Stanislas-Jean


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GlennLeDrew
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Re: Ashen Light - Redux new [Re: stanislas-jean]
      #5772118 - 04/02/13 03:15 AM

The value of 6% I chose applies to about the 'mid' scotopic regime, where surface brightness is that of a relatively bright night sky but below the color detection threshold. That there is (we assume) a 'hard' edge separating the night sky and the night side limb, we could expect better detection of a brightness difference,

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GlennLeDrew
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Re: Ashen Light - Redux new [Re: stanislas-jean]
      #5772139 - 04/02/13 03:45 AM

The value of 6% I chose applies to about the 'mid' scotopic regime, where surface brightness is that of a relatively bright night sky but below the color detection threshold. That there is (we assume) a 'hard' edge separating the night sky and the night side limb, we could expect better detection of a brightness difference, perhaps at the 2-3% level.

But at these subtle levels of difference, it might be imperative to occult the sunlit crescent. Suppose an optical system (including the eye, when employed) scatters 0.1% of the light from any discrete source as veiling glare in a Gaussian whose 2-sigma diameter (containing 95% of the light) is 3 degrees on the retina. For -4.4m Venus, the *mean* surface brightness of the glare alone is 23 magnitudes per square arcsecond; the glare would be notably brighter the nearer the crescent. The magnification must be sufficient to move at least the dark limb opposite the crescent well enough outside the brighter glare zone so as to not have the contrast impaired. If at the spot examined glare amounts to the same intensity as the sky, the contrast of any feature seen through these glows is halved.


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stanislas-jean
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Re: Ashen Light - Redux new [Re: GlennLeDrew]
      #5772213 - 04/02/13 06:40 AM

Scotopic, this might be, not in mesopic mode.
Stanislas-Jean


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stanislas-jean
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Re: Ashen Light - Redux new [Re: GlennLeDrew]
      #5772233 - 04/02/13 07:04 AM

In mesopic mode that depends so much on the observer abilities.
Under some light levels this may reach 0.5% (for resolution), the observer very calm, steady on a long time under the obeserved light conditions, etc...
My tests on distanced target goes to 0.05cd/m2 on a simulated image placed at long distance (50" disque size at more than a km distance with just on the side an illuminated part lighted violently behind).
That's making a ratio of 100 000 may be a little more, difficult to measure exactly with the lux meter. Therefore a difference magnitude (an assessment in terms of a ratio expressed in any unit) of 10 so around m6 for the simulated dark side.
This is not cross-checking the ccd procedure.
The levels involved by the ccd procedure would involve lower levels than my tests.
So the status is:
light glare is more effective than expected even with the use of an occulting side than produce still diffraction edge light even with a crescent placed few " of arc from the edge.
The light reported is present well, not an illusion but at fortiori a produce of the investigation method of observation.
This is my explanation of the situation with regards to the ccd procedure results.
It remains the fact that the solar light reflexion by moon, earth and planets on the dark side of venus involves an amount of 0.001cd/m2 around. Corresponds to 4 magnitude deeper than my visual abilities , so about 14 magnitude deeper than the crescent level.
This amount of light which is actual would be revealed by ccd procedure in any color channel because a solar light at the 1st approach.
Here this is not cross-checked.
Always cross-checking by different ways for assuming verifications and completeness.
Stanislas-Jean


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Rick Woods
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Re: Ashen Light - Redux new [Re: stanislas-jean]
      #5778948 - 04/05/13 03:21 AM

I've been reading some on the AL. It seems the most reasonable explanations include auroral activity; airglow; red-hot surface glowing through thin cloud cover; and lightning. There is a slight bit of photographic and spectroscopic evidence, but nothing you could really point to and say "that's the cause of the AL".

Proceeding on the premise that it's a real, Venusian phenomenon, I'd like to propose a couple more ideas, for discussion/shooting down/ridiculing:

1) The obvious, a combination of all the above. When they're all going on and the conditions are right, the light appears.

2) Venus has an atmosphere 90 times denser than that of Earth. Could this density under certain circumstances bend, or extend, the light from the daylight side into the dark side? I'm groping on this one, and I'm sure it's full of holes, but maybe?

3) Some sort of airborne, phosphorescent life form that periodically emits the light (mating season, seasonal atmospheric changes, ?). Not so unbelievable - just look at the black smokers and other extremophiles right here on Earth.

The testimony I've read here and in other places is just too compelling to believe that this is just an illusion. I really feel something is happening on Venus and once in a while, we get to see it.


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Edward E
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Re: Ashen Light - Redux new [Re: Rick Woods]
      #5779446 - 04/05/13 11:39 AM

I agree with you Rick, I'm keeping an open mind on the AL BUT when I "saw" the AL and had two others (non astronomy interested) look (neither of the two saw or talked to the other before looking) without telling them what the scope was pointed at and each commented that it was a nice looking crescent moon with the unlit side visible until they looked up and noticed that there was no Moon in the sky; it is hard for me believe that three of us were having the same illusion. I can also believe that there are no CCD images of the AL since it is a fairly rare event. In 35 years of watching Venus I have only seen the AL that one time. If the AL is just an illusion created by the brain then statistically I should have seen the illusion more than once in 35 years observing Venus.

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Rick Woods
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Re: Ashen Light - Redux new [Re: Edward E]
      #5779670 - 04/05/13 01:51 PM

That's what I mean. People who have actually seen it, never have any doubts again. I see this over and over in the papers and books I've read.

Sean W. said he tried to image it unsuccessfully at a time when someone was reporting a sighting. What we need is a visual observer, also imaging-savvy, who actually sees the AL unambiguously, and tries to image it immediately. If we can get that, we'll really have a chance at some answers.


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Re: Ashen Light - Redux new [Re: Edward E]
      #5779686 - 04/05/13 01:56 PM

Rick, in my AL report 2012, I sustained the possibility to get light diffusion into the venusian atmosphere (cusp extension cannot be without this).
Idea 2.
Idea 1 is actual because reported.
Idea 3 why not but a speculation.
But a new time when we have a physical assertion consisting in the presence of solar light reflexion by planet atmospheres as the earth that can involve a calculated amount of light, this amount has to be reported by the ccd procedure given before.
Any assessment and result for a full pertinence needs to be cross checked by other means. Here we have this possibility offered.
So my conclusion is that the ccd procedure is not fully achieved and completed. Some calibration operation needs to be done in order to qualify the light limits reached.
But this remains a serious way for assessment but not under full completeness.
The conclusion can be also: no enough data and observations for making some final conclusions.

Edward, on the 80ies I never saw the AL, only this recent conjunction of Venus on 2012.
I used an occulting side that created some diffraction adge well seen at the eyepiece, but when you shifted few seconds of arc behind the crescent from the edge, the diffracted light didn't appear at the eyepiece.
This test was done when the phase was around 0.5.
Withis I asked a second observer to set when the phase was under 0.3 the crescent on the same procedure but unknown from me in order to get the dark side appearing along the edge. To me identify where venus dark side is.
The light was suffieciently high for recognising the right location.
I think there is no illusion involvement with this kind of test.
Now we have the ccd procedure assessment which is a serious objection but not calibrated.
Is the light polarised under some plan? I didn't investigate this during the observation period.
Iknow with such polarimeter use that some planet details may be fading a lot at the eyepiece.
May be the answer may be not so straightforward as we can imagine.
Subject not closed.
Stanislas-Jean


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buddyjesus
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Re: Ashen Light - Redux new [Re: stanislas-jean]
      #5779775 - 04/05/13 02:39 PM

shame the venus climate orbiter failed. would have given great data on this(among other things.)

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Re: Ashen Light - Redux new [Re: buddyjesus]
      #5779782 - 04/05/13 02:41 PM

I think the aurora is the most likely explaination. Venus has a weak magnetic field that might cause a whole globe aurora. I wonder what color aurora would be produced in a CO2 atmosphere.

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Edward E
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Re: Ashen Light - Redux new [Re: Rick Woods]
      #5779904 - 04/05/13 03:29 PM

I'm not big on Twitter or E-mail alerts but here is where both would come in handy. Anyone interested in observing Venus and the AL possibility, could subscribe to a "Venus Watch" account and if anyone "sees" the AL they could send out an alert out so that others can be alerted and have a look/take data. The results could then be shared here on CNF.

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starbux
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Re: Ashen Light - Redux new [Re: buddyjesus]
      #5779934 - 04/05/13 03:38 PM

I have an interesting question about how much of Earth's own reflected light *might* contribute to the Ashen Light. If (a crescent) Venus is known to cast shadows on Earth, how much more light would (a full phase) Earth cast upon Venus' clouds?

Even if no one seriously entertains the idea that the cause of Ashen Light is the same as Earthshine, I would be interested to know exactly how much of Earth's reflected light reaches Venus from those who can figure it out.


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Re: Ashen Light - Redux new [Re: starbux]
      #5780070 - 04/05/13 04:23 PM

Quote:

I would be interested to know exactly how much of Earth's reflected light reaches Venus from those who can figure it out.



Well, as a rough estimate:

Venus (at its closest) is 100 times as far from the Earth as the Moon is, so the intensity of Earthshine on Venus will be at most 1/10,000 that of Earthshine on tthe Moon. We can reduce this by a factor of approximately 10 as Venus is much more reflective than the Moon, but the intensity will still be 1/1,000 that of lunar earthshine, and usually very much less (as it's only when Venus very near to inferior conjunction and therefore not observable in a dark sky that it will be as close as 25 million miles).

When Venus is at maximum brightness, the increased distance will reduce the brightness of the earthshine to less than 1/2,000 of that seen on our own Moon.


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GlennLeDrew
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Re: Ashen Light - Redux new [Re: brianb11213]
      #5780367 - 04/05/13 07:14 PM

To amplify on Brian's reasoning..
Earthshine on the Moon has the surface brightness of about 14 magnitudes/arcsecond^2, which equals that of the brightest nebulae (a number of planetary nebulae and the central region of M42.)

Combining the distance (100) and albedo (6) ratios, earthshine on Venus will be 10,000 / 6 = 1,700 times fainter. That's -2.5 Log 1,700 = 6.5 magnitudes fainter.

And so earthshine on Venus could be expected to be 14 + 6.5 = 20.5 magnitudes/arcsec^2. That's the surface brightness of a suburban or semi-urban night sky.

If this ashen light could be seen *by itself* (sunlit crescent invisible) in a same-brightness sky, its light would add to the sky glow and so appear twice as bright; that would be fairly decent contrast and hence be readily visible. Indeed, such a hypothetical situation as the ashen light *in isolation* would be detectible (with difficulty) in a sky some three magnitudes brighter, or 17.5 MPSAS.

The key is the contrast-wrecking effects of the blazing sunlit crescent (mere arcseconds distant!), twilight or sky glow and the zodiacal light. Even the use of an occulting device at the focus may not be so efficacious due to the very tiny angular separation between sunlit and night sides, and the efficiency of forward scattering by the atmosphere. In other words, might there be present sufficient diffuse light from the (occulted) bright crescent 'hazing' much of the immediate surroundings? (This last potential concern is something I know little about as a quantity.)


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Re: Ashen Light - Redux new [Re: Rick Woods]
      #5780468 - 04/05/13 08:38 PM

Quote:

That's what I mean. People who have actually seen it, never have any doubts again. I see this over and over in the papers and books I've read.

.




And Rick I was one of those believers till the day I saw the ashen light simulated. Then it lost all question for me. I ve sen it simulated in photos - even of moon pics looking like they had earthshine till the actual moon was covered up and the earthshine literally vanished. And the illusion persisted and every time, it vanished.

My take anyway.

Pete


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azure1961p
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Re: Ashen Light - Redux new [Re: Rick Woods]
      #5780473 - 04/05/13 08:40 PM

Quote:


Sean W. said he tried to image it unsuccessfully at a time when someone was reporting a sighting. What we need is a visual observer, also imaging-savvy, who actually sees the AL unambiguously, and tries to image it immediately. If we can get that, we'll really have a chance at some answers.




That shouldn't be required Rick. If the report is out as in an alert and the cam is rolling then it doesn't matter if the imager is making a visual on it or not. If its active its active.

Lol don't hate me man.

Pete


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Re: Ashen Light - Redux new [Re: azure1961p]
      #5781260 - 04/06/13 08:24 AM

I think the alert procedure would be usefull for confirmation or not a confirmation.
A good way for cross checking results.
Stanislas-Jean


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Re: Ashen Light - Redux new [Re: GlennLeDrew]
      #5781267 - 04/06/13 08:27 AM

I think this calculated or evaluated amount of light would impress a ccd chipset at the level it is.
From my opinion not accessible to eyes, but by ccd surely and this is not with regards to what was brought with the ccd procedure.
May I insist on.
Stanislas_Jean


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Re: Ashen Light - Redux new [Re: Rick Woods]
      #5781573 - 04/06/13 11:15 AM

Quote:

That's what I mean. People who have actually seen it, never have any doubts again. I see this over and over in the papers and books I've read.




The same can be said of visual observations of canals on Mars and multiple divisions within Saturn's rings. These phenomena were reported with absolute certainty by many of the best visual observers of the 19th Century. And they all were wrong. There are no canals on Mars. With but a few exceptions, the multiple divisions reported within the rings of Saturn do not exist. Belief is not evidence and, for those questions whose answers are determined by evidence, belief is irrelevant.

Visual observation is inherently subjective and fallible. The act of "seeing" is as much--if not more--a mental interpretive process as it is an experience of external physical stimuli. The mind of the person making the observation is the final filter that interprets and brings meaning to the raw data collected by the eye. As such, mental interpretation is inextricably linked to the act of observing. And mental interpretation is influenced by the subjective beliefs of the person doing the interpreting. This makes visual observing wholly subjective and renders the act, as scientific evidence, of minimal value.

How can a person see what isn't actually there? It's simple. Just believe.


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Re: Ashen Light - Redux new [Re: BillFerris]
      #5781857 - 04/06/13 01:13 PM

You have always the possibility to control what is collected by other means, visual or ccd.
Just to find them and undertake them to get more pertinence and get confortable views, not opinions.
Stanislas-Jean


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Re: Ashen Light - Redux new [Re: azure1961p]
      #5781959 - 04/06/13 02:14 PM

Quote:

Quote:

That's what I mean. People who have actually seen it, never have any doubts again. I see this over and over in the papers and books I've read.

.




And Rick I was one of those believers till the day I saw the ashen light simulated. Then it lost all question for me. I ve sen it simulated in photos - even of moon pics looking like they had earthshine till the actual moon was covered up and the earthshine literally vanished. And the illusion persisted and every time, it vanished.

My take anyway.

Pete




But Pete; have you ever driven down a highway in the summer? I have, and seen a large, perfectly normal looking body of water in the road ahead of me, that disappears as I approach it. But, I've also seen genuine bodies of water.

The fact that something can be simulated does nothing to negate its reality. (Which may or may not bear on the case here.)


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Re: Ashen Light - Redux new [Re: azure1961p]
      #5781973 - 04/06/13 02:23 PM

Quote:

Quote:


Sean W. said he tried to image it unsuccessfully at a time when someone was reporting a sighting. What we need is a visual observer, also imaging-savvy, who actually sees the AL unambiguously, and tries to image it immediately. If we can get that, we'll really have a chance at some answers.




That shouldn't be required Rick. If the report is out as in an alert and the cam is rolling then it doesn't matter if the imager is making a visual on it or not. If its active its active.

Lol don't hate me man.

Pete




I don't agree. We need to eliminate as many variables as possible (e.g. different locations, different local conditions, etc). The imager might not see the AL from the location from which it was reported. Someone who definitely sees it, then tries to image it right then, right there, would provide a real benchmark. That's the only way to really test anything; narrow the test down to the simplest possible parameters. If it was seen, and couldn't (or could) be imaged, that would be a valuable piece of information.

LOL, I don't hate anyone! I enjoy the exchange; and I'm not a "true believer" by any means. I just don't see sufficient reason (yet) to assume its an illusion. (And, I guess I like to think there are still mysteries in the Solar System that I could try to solve. )


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Re: Ashen Light - Redux new [Re: BillFerris]
      #5781986 - 04/06/13 02:30 PM

Quote:

Quote:

That's what I mean. People who have actually seen it, never have any doubts again. I see this over and over in the papers and books I've read.




The same can be said of visual observations of canals on Mars and multiple divisions within Saturn's rings. These phenomena were reported with absolute certainty by many of the best visual observers of the 19th Century. And they all were wrong. There are no canals on Mars.




Bill,
There are multiple divisions in Saturn's rings; and the canals of Mars have been shown to be the result of many different things: contrast effects, fine detail run together at the limits of resolution, genuine linear features (Vallis Marineris), etc etc. The causes of these sightings is pretty well established. And, they were actually photographed in the early 20th century. Many people still see them sometimes. There are no great waterways built by a noble race of Martian engineers; but the features that were misinterpreted as such, absolutely do exist.

So, this isn't quite the same. If it's an illusion, it hasn't yet been identified. If it's not, the cause is still a mystery. Patrick Moore was a skeptic about all this stuff. He never saw a canal in his life; but he saw the AL many times.


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Re: Ashen Light - Redux new [Re: Rick Woods]
      #5782014 - 04/06/13 02:46 PM

My take? That there are *vastly* more visual reports (by ever fallible humans) than photographic (none in the visual band?) is telling in the extreme.

Until *concrete*evidence surfaces, I will treat this as merely illusion.

Not for one moment will I entertain the notion that it is 'difficult' to image this phenomenon which is apparently so detectible visually.

The biggest red flag for me? That this has been reported in DAYTIME! There hardly exists a more impressive piece of evidence of the power of illusion.


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Re: Ashen Light - Redux new [Re: GlennLeDrew]
      #5782210 - 04/06/13 05:11 PM

Ok Rick. You need to sit down for this.

There was a body of water on the highway. In every case the lake evaporates before you get there because the macadam is that hot.

Tis true. Lake Superior used to be an immense highway but the water won.


Pete


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Re: Ashen Light - Redux new [Re: GlennLeDrew]
      #5782475 - 04/06/13 07:30 PM

Quote:

My take? That there are *vastly* more visual reports (by ever fallible humans) than photographic (none in the visual band?) is telling in the extreme.

Until *concrete*evidence surfaces, I will treat this as merely illusion.

Not for one moment will I entertain the notion that it is 'difficult' to image this phenomenon which is apparently so detectible visually.




All true, and all the more reason that a good visual observer needs to see the effect, and immediately image it. AFAIK, this hasn't occurred.

Quote:

The biggest red flag for me? That this has been reported in DAYTIME! There hardly exists a more impressive piece of evidence of the power of illusion.




I dunno. I have to take into account the caliber of the people who saw it (Cruikshank and Hartmann), before believing it to be illusion.

I'm ready to concede that a large number of sightings are probably illusionary; but there are many instances of sightings by people who are a bit more savvy, and less susceptible to these illusions.

It may be all an illusion, but that hasn't been proven; and to ignore a potentially important phenomenon because it's not easily explained seems wrong to me. I guess my attitude is the opposite of yours: I put the burden of proof on those who say it doesn't exist, whereas you're putting it on those who say it does. I know it's harder to prove a negative; but explaining the credible sightings that have occurred would go a long way. All I've seen so far is arguments as to why the sightings couldn't have happened; no attempt to explain what was actually seen.


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Re: Ashen Light - Redux new [Re: azure1961p]
      #5782481 - 04/06/13 07:31 PM

Quote:

Ok Rick. You need to sit down for this.

There was a body of water on the highway. In every case the lake evaporates before you get there because the macadam is that hot.

Tis true. Lake Superior used to be an immense highway but the water won.


Pete




I hate when that happens! (The GLC's would never allow it.)


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Re: Ashen Light - Redux new [Re: GlennLeDrew]
      #5783091 - 04/07/13 04:30 AM

Quote:

My take? That there are *vastly* more visual reports (by ever fallible humans) than photographic (none in the visual band?) is telling in the extreme.



Even if you take the dogmatic view that the AL does not exist, this is actually rather surprising since digital images are so easy to fake.

Quote:

Not for one moment will I entertain the notion that it is 'difficult' to image this phenomenon which is apparently so detectible visually.



Sorry but, although detection of fine, low contrast detail is much easier with digital imaging techniques than it is visually, the contrast between the AL and the lit crescent is so great that digital cameras are going to struggle - stray light is going to overwhelm the sensor - this is the sort of thing that the human eye is still better at (and maybe always will be).

Quote:

The biggest red flag for me? That this has been reported in DAYTIME! There hardly exists a more impressive piece of evidence of the power of illusion.



There are certainly psychological factors here, and the intensity of the AL (if real - whether auroral or reflective in nature) should rule out observation in daylight or bright twilight. But the fact that there are incorrect observations in the record shouldn't rule out any possibility of the reality of the AL.

Personally I have not seen the AL and have a great deal of doubt about the veracity of many of the reported observations ... but I remain sufficiently sceptical to admit that the AL might be seen, occasionally, faintly or very faintly, against a dark sky and with the benefit of exceptionally clean optics, clear transparent air and an occulting bar.


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Re: Ashen Light - Redux new [Re: brianb11213]
      #5783135 - 04/07/13 05:33 AM

a_ The problem of the ccd is this is not a WB problem but a settlement of light levels that must be calibrated.
The calibration phase is missing.
I think this is not a matter of dogme but rather a matter of trial tests with known characteristics of details (as it can be created on a cible to be tested).

b- This eye ability to separate low light levels near high lighted surfaces can be also tested on cible.
Personnally it can be reached for myself until 0.05cd/m2 with a side of more than 5000cd/m2. Ratio 100 000.
If the AL doesnot exist and constitutes an illusion it remains to be detected the light level on the dark side of the earth shine light reflexion (evaluated to be 0.001cd/m2)
For the moment the ccd procedure on cause didn't reveal this amount of light. This is strange. Therefore the calibration sequence is missing, not the application only of a pre-supposed method ability.

c- Personally on 2 days I observed the AL presence, this was, during daylight (pure sky), twilight (about 1 hour before sunset), nautical sky (1 hour after sunset).
With different filters (blue, green, red), different apertures. You may refer to them.
With oculting side (with the test method ddescribed before here in other posts) and not.
The AL was here with different intensities according the time, the color of observation, the aperture.
Ididn't used a polariser and I think might do.

The problem of the data is there too partial, not enough and must be analysed rather on technical point of views than against generalities.
Test methods has to be acurate, calibrated and tested against references.
Nobogy here, including me, introduced metrology data, ccd being only a picture maker and not a photometer.
We need here a photometer, calibrated, for answering correctly.
I think an investigation needs to be performed with polarimetry on the subject.
Stanislas-Jean


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Re: Ashen Light - Redux new [Re: brianb11213]
      #5783136 - 04/07/13 05:37 AM

[Originally an accidentally sent first portion of the following post... ]

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Re: Ashen Light - Redux new [Re: brianb11213]
      #5783138 - 04/07/13 05:41 AM

Brian,
You are correct about detectors (and film) where glare is concerned, as they have less dynamic range than the eye. But a suitable occulting device near the focus will obviate this. The light blocker need not be made so as to have the shape of the sunlit crescent; as we're concerned only with the night side of the planet, the occulter can be a large plate, on one edge a small, round notch of roughly suitable radius being made. Venus is aligned with the notch, and the scope moved so as to just fully hide the bright crescent beyond the edge of the notch.

The occulter must be placed as close to the sensor as possible, so that it's in reasonably sharp focus.


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Re: Ashen Light - Redux new [Re: GlennLeDrew]
      #5783147 - 04/07/13 05:55 AM

If you place the crescent limit just on the edge of the occulting side, you have noticeable light diffraction accessible to eyes even in daylight.
With few seconds of arc shift of the crescent limit beyond the occulting edge, this is disappearing.
I did the exercise. Perform this when you donot notice the AL presence or what it seems, so when the planet phase is around 0.5 for having the best conditions of test.
Occulting side use has needs.
Stanislas-Jean


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Re: Ashen Light - Redux new [Re: GlennLeDrew]
      #5783150 - 04/07/13 06:00 AM

Stanislas-Jean,
For the purpose of *detection*, calibration is not required. One is merely looking for any brightness level above that of the sky. If the sky glow is recorded well enough above the instrumental noise, and all sources of glare and scatter are taken care of to the extent possible, then one has a sufficiently good image with which to say 'yes' or 'no' for the detection.

That same image, if not processed, can then be measured for the determination of the brightness ratio, or contrast. And if one knows the sky brightness at the time of the image, the intrinsic surface brightness on the planet (sky subtracted) follows directly.

If the visual observer is using a sensor--the eye--which is not calibrated, why then must a camera be calibrated beforehand? Just as the eye detects a brightness ratio, so does the camera. What's important is that the exposure put the sky glow sufficiently above the camera noise, and not more than about 2/3 of the way to saturation. That's a pretty good margin which allows several f/stops' range on exposure.


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Re: Ashen Light - Redux new [Re: GlennLeDrew]
      #5783153 - 04/07/13 06:06 AM

How do you consider the fact that the amount of light created by earthshine reflexion on venus dark side being above of the background sky light level not revealed by the chipset?
Stanislas-Jean


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Re: Ashen Light - Redux new [Re: GlennLeDrew]
      #5783168 - 04/07/13 06:17 AM

Quote:

detectors (and film) where glare is concerned, as they have less dynamic range than the eye. But a suitable occulting device near the focus will obviate this.



But there is still scatter in the optics positioned before the occulting bar, and in the atmosphere.

I suspect we are going to need observations made with a coronograph from either a high altitude desert location or from a high altitude balloon or satellite to solve the question of Venusian ashen light with any degree of conclusiveness.


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Re: Ashen Light - Redux new [Re: brianb11213]
      #5783390 - 04/07/13 09:24 AM

Stanislas-Jean,
If, after taking due care to minimize extraneous light, Venus' night side is not detectably brighter than the sky, then we can assign a *maximum* intrinsic surface brightness. For example, suppose the sky has SB = 19, and Venus' night side is identically bright (no detectable ashen light at all.) furthermore, suppose that, based on the camera's bit depth and its noise level in the image we deduce that we should discriminate a brightness difference of 2%. We know then that the night side cannot be any brighter than 4.3 MPSAS below the sky brightness, or 23.3 MPSAS.


Brian,
Indeed, as I have pointed out in earlier posts, simply occulting the source at the focus does not quell atmospheric and instrumental scatter.

But the eye has to deal with these as well. To a camera, this will be *very* much less injurious than the blazing, bloomed, far over-saturated blob of light which would be the sunlit portion. But with an occulter in place, the residual scatter most assuredly will be no more of an impediment than it is to the eye.


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Re: Ashen Light - Redux new [Re: GlennLeDrew]
      #5783534 - 04/07/13 10:52 AM

To elaborate on one point: The daytime observation of Cruikshank and Hartmann revealed not a brighter unlit side of Venus, but rather a slightly coppery colored one against the blue background.
The effect was one of color, not brightness.

(PS: See S&T, March 2012, pg 53.)

Edited by Rick Woods (04/07/13 11:13 AM)


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Re: Ashen Light - Redux new [Re: Rick Woods]
      #5783771 - 04/07/13 01:06 PM

Not only Rick because the AL coppered color you recall was effectively reported with a moltenned appearance.
However this moltenned appearance was also noted on the sky around.
This comment is strange and make an objection.
Personnally for reporting, this AL color was seen also moltened coppered color (rather grainy than moltened) but not on the sky around and concerning the whole dark side part or only partially without the filter use and AL seen also under color filters R, G, B.

Glenn, I understand what you mean about the ccd procedure used. My evaluation of this situation for the moment is that the earthshine reflection conducts to a light level being above the back ground skylight level used as a reference in the ccd procedure (light level being few above the noise of the ccd chipset, you recalled). This is qualitative settlement but
this point is still disturbing me and I am wandering who did this acurate evaluation by calculation and which results he get.
I would exercise these verifications.
Stanislas-Jean


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Re: Ashen Light - Redux new [Re: stanislas-jean]
      #5784071 - 04/07/13 03:26 PM

The coppery or warm tone would seem to he easily explained away as a contrast effect against so much blue sky, day or evening. Surely you've seen the effect if this in doublestars where the blue companion can make the primary (or vice versa) take on a decidedly warm hue. In this case because the ashen light is seen or seemed to possess a certain brightness however faint then it would make all the sense in the world this take in the hue it does.

How though this topic keeps thriving in the light of some pretty damning evidence is beyond me. I thought Glenn said it all rather succintly .


Pete
PS: oh, I know where you going to go with this rebuttal Stan: the doublestar analogy is invalid because its point sources versus extended object. That's irrelevant as any kind of counter claim. What differences arise are more an exercise in semantics than anything that would matter one way or the other.


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Re: Ashen Light - Redux new [Re: azure1961p]
      #5784722 - 04/07/13 08:30 PM

Pete,

I sure haven't seen any damning evidence yet. And the double star analogy is *really* thin. And the thread continues because it's an interesting topic, and is, still, an unsolved mystery.


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Re: Ashen Light - Redux new [Re: GlennLeDrew]
      #5785072 - 04/07/13 11:49 PM

the venus watch yahoo group has an image available for making venus occultion masks with 3 different arcs on it(for different magnifications.) I didn't see anyone use it last season though.

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Re: Ashen Light - Redux new [Re: azure1961p]
      #5785202 - 04/08/13 02:02 AM

This doesnot explain the fact when the occulting side is used the AL is still visible on the dark side and sometimes with this coppered color and grainy appearance.
Take in consideration the procedure used with the occulting side and with the second observer who locates the planet aleatory to be found by the 1st obaserver who doesn't know where the dark side is actually.
I suggest you perform this, this is very instructive for ourselves.
Stanislas-Jean.


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Re: Ashen Light - Redux new [Re: stanislas-jean]
      #5785212 - 04/08/13 02:16 AM

Sirius double star was well separated in a 3" achromat well designed on the 80ies (not interested now with doubles).
This needs a high doublet where the main star is still a luminous point without spikes, the sky around remaining black deeply. All the scopes on use are on this level (absence of light diffusion around a strongly lighted surface or point): this is a need for this kind of exercise on venus.
The observation of doubles is interresting on that view but a 1st step.
Stanislas-Jean.


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Re: Ashen Light - Redux new [Re: stanislas-jean]
      #5785250 - 04/08/13 03:25 AM

Persistence of vision.

Pete


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Re: Ashen Light - Redux new [Re: azure1961p]
      #5785330 - 04/08/13 06:55 AM

That persists.
Stanislas-Jean


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Re: Ashen Light - Redux new [Re: stanislas-jean]
      #5786116 - 04/08/13 02:10 PM

Indeed,
If the sunlit crescent could be well occulted so that it's fully blocked, an observation of a night side illumination would be more secure.

Note, however, that there can remain one or more sources which can introduce uncertainty.

1) If the occulter is made so as to have a 'concavity' which permits the seeing of the maximum area of the night side, and if the occulter is readily seen as a black silhouette, that very concavity could well provide a 'frame' for the visual system to provide a spurious 'filling in' of the circle.

2) There will likely be some atmospheric and instrumental scatter, appearing as a brightening of the sky toward the occulted crescent. Such a gradient could have some bearing on the perception of a spurious glow.

An image would definitely be preferred in any case, as then it could be objectively measured, with the capability to find the limb and ascertain if it's both well defined and smoothly circular, of the expected size.


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Re: Ashen Light - Redux new [Re: GlennLeDrew]
      #5786413 - 04/08/13 05:02 PM

The question of the occulting is important to define.
Frankly, when spurious light is occuring this does not create a circular appearance (a dark side lighted) but rather a lighted band with a decreasing light intensity. The width of the this band is the diameter of venus.
For annealing this it is just necessary to shift the crescent few seconds of arc behind the occulter edge in order to be fully covered by the occulter.
This is the condition to achieve for not having spurious (diffraction edge).
When some AL appears on the sky the dark side of venus not occulted appears lighted without the vision of the crescent.
For the occulter I am using piece of dense argentic films (the TP 2415 from kodak is excellent, the opacity is easy to get, it is unsensitive to moisture, it remains at home some coils still not used. To check the density we have access to a densitometer used for industrial radioscopy). Just to glue the oculter on the FOV ring of the eyepiece, so just at the focus plan, less the film thickness.
My results were got with this. The drawing reports were done under pure sky.
At final after 2 days tests as described, I didn't use any occulter, evaluating that its useless role.
Long distance tests on cibles convinced me also to abandon the use of the occulter bringing in fact more trouble than solving some hypothetic situation.
You know the separation of double star as Sirius, as a 1st approach and long distance test on cibles that create sensitive surfaces lighted with a known light ratio.
Stanislas-Jean


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Re: Ashen Light - Redux new [Re: stanislas-jean]
      #5786769 - 04/08/13 08:19 PM

S-J,
I gather you're stating that the occulter is not necessary? From the standpoint of diffraction, certainly this is the case. But sensor (eye or camera) saturation without it introduces a very real potential for masking of the dim phenomenon we're trying to detect. Due to the excessive brightness ratio between day and night sides, and most crucially their proximity, every effort to block that bright source can only pay dividends.

For one thing, if the visual detection of the AL is seen to depend, even slightly, on the *presence* of the sunlit crescent, this must be seriously considered as evidence for the 'filling-in-the-circle' illusion.


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Re: Ashen Light - Redux new [Re: GlennLeDrew]
      #5786859 - 04/08/13 09:06 PM

I'd like to slip in here and thank everyone for your opinions and viewpoints so far. I'm really enjoying this thread - lots of good stuff here!


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Re: Ashen Light - Redux new [Re: Rick Woods]
      #5787282 - 04/09/13 02:20 AM

Thanks Rick for your presence.
Glenn, yes this is my conclusion after performance of 2 kind of tests.
Intellectually this is disturbing for sure but this is not a fact but a result.
I know that when making ccdd images (I did) the crescent is invaded by glaring. But I think this is light levels concern and probably depending on the observer also.
We take an example: driving during night with people on the opposite way with lights full and you following a driver with its little red lights more or less powerfull, under rain.
This is an analogy but similar.
Now all these assessments doesnot constitute prooves.
And for the moment the ccd procedure is the way for prooving.
This is what I noted through the present CN forum.
And the fact that an AL light was seen under conditions we know that merits deeper analysis, because the light is not illusory, but can the result of physical processus created by the observation method or the kind of light observed (an edge create diffracted light with an amount of polarised light).
Consider the fact that, for ccd too, that light are the result of cause that can be splitted according to calc.
The eye has the possibility to merge a certain calc (that correspond to a certain light and a cause) and avoid the others (the drivers analogy is correct for illustration of this, it is almost impossible to discerm the red lights if you consider only the overall scene).
Stanislas-Jean


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GlennLeDrew
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Re: Ashen Light - Redux new [Re: stanislas-jean]
      #5787421 - 04/09/13 05:50 AM

S-J,
There are some confusing parts in your previous post.

I'm still not certain whether you say *to use* an occulter or *not to use* an occulter.

You often mention diffraction. I feel that this by itself poses no *significant* problem to the detection of AL. With any reasonable size telescope, the diffraction intrudes into the night side only some several arcseconds, compared to the disk diameter of the better part of an arcminute. Moreover, diffraction is always present, irrespective of the presence or lack of an occulter.

You have often mentioned polarization. The combination of eye and telescope introduces polarization only (?) when light is reflected at an angle somewhere in the system, as when a diagonal is used. I should think a straight-through arrangement will not result in instrument-induced polarization.

Is polarization of real concern? The object, by virtue of the scattering property of the cloud droplets, should not be expected to polarize light itself. And if the source light is not polarized, instrumental polarization cannot alter the contrast of the view.

Of course, our atmosphere does partially polarize that light it scatters. The maximum polarization occurs at some angle (around 60 degrees?) from the source. Given that Venus is rather closer to the Sun than this, about 25-30 degrees and less, the polarization of scattered sunlight is weaker. And so a polarization filter is less efficacious.

Does the atmosphere polarize the light of objects seen through it? I don't think so; not to any notable extent anyway. If this is the case, then atmospheric polarization cannot alter the contrast of the components making up the scene beyond. All we can do is exploit atmospheric polarization, by cross-polarizing at the appropriate angle in order to dim the sky glow relative to the scene beyond. (Everything will be dimmed somewhat, but the sky more so.)

I do wonder about the degree of polarization of light from the object which is scattered and seen in the immediate vicinity of the object itself (i.e., in direct forward scattering.) I believe such light is not really polarized, and if it is it would be effectively, and weakly, circularly polarized. In such case, there may be no effective way to suppress the glow of scattered light emanating from Venus' day side.


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stanislas-jean
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Re: Ashen Light - Redux new [Re: GlennLeDrew]
      #5787526 - 04/09/13 07:49 AM

May be it is not clear enough from me.
I am speaking about the diffraction edge created by the edge of the occulter: this effect can be seen visually at the eyepiece.
The light is spreading perpendicullary to the edge. You have to shift the lighted part of the planet disk fully behind the occulter for avoiding this.
After an exhaustive campain of tests on 2 days, with and without an occulter my conclusion was that the use of the oculter brought actually nothing consistent.
This was reinforced with the practice of tests on long distanced cibles consisting in a part highly lighted and a part low lighted with a known ratio of intensities.
Also same conclusion, the occulter bring nothing more and through was determined some possibilities: a ratio of 100 000 was still possible, the lighted part being 5000cd/m2.
Hope this is clearer.
All the numbers mentionned in my old posts were coming from these tests.
Stanislas-Jean


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buddyjesus
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Re: Ashen Light - Redux new [Re: stanislas-jean]
      #5788713 - 04/09/13 05:02 PM

gotcha

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stanislas-jean
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Re: Ashen Light - Redux new [Re: buddyjesus]
      #5789483 - 04/10/13 01:48 AM

Sorry I donot understand, can you be clearer about.
Stanislas-Jean


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Rick Woods
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Re: Ashen Light - Redux new [Re: stanislas-jean]
      #5789509 - 04/10/13 02:24 AM

Stan,

"Gotcha" is American slang for "I've got you", which in this case means "I understand now".


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stanislas-jean
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Re: Ashen Light - Redux new [Re: Rick Woods]
      #5789534 - 04/10/13 02:39 AM

Yes OK Rick, my english is not excellent.
Thanks.
Stanislas-Jean


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buddyjesus
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Re: Ashen Light - Redux new [Re: stanislas-jean]
      #5791384 - 04/10/13 09:58 PM

sorry for using slang given the people in the discussion. I will be more mindful in the future.

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azure1961p
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Re: Ashen Light - Redux new [Re: buddyjesus]
      #5791550 - 04/10/13 11:14 PM

Rodger Wilco there Buddy-j,

Pete


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Rick Woods
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Re: Ashen Light - Redux new [Re: azure1961p]
      #5798913 - 04/14/13 05:11 PM

I have a book on the way; "Handbook of the Physical Properties of the Planet Venus", a NASA publication from the 60's (or maybe 70's). I'm hoping for a good review of the Ashen Light phenomenon in it. I have the equivalent publication for Mars, and it has great coverage of the Blue Clearing and several other topics.

These NASA handbooks are outstanding! The Mars one is available free as a downloadable PDF several places on the web. The Venus one may be also, but I didn't look (printing costs would have been greater than the cost of buying it.)


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Rick Woods
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Re: Ashen Light - Redux new [Re: Rick Woods]
      #5801932 - 04/16/13 02:34 AM

The book came today; NASA SP-3029 (1967). It only has about a page and a half on the Ashen Light, though. Pertinant quote:

"Weinberg and Newkirk were unable to identify any emission lines on 20 spectrograms taken of the unilluminated portion of Venus in 1959. But their failure in 1959 and Newkirk's success in 1958 are consistant with independent visual searches during these two periods. However, Weinberg and Newkirk are not convinced of the reality of the ashen light phenomenon and, at present, it must be concluded that there is neither a satisfactory explanation nor definite proof of its existance."

There's a bit of explanatory test before this; but they really give it short shrift, and end up with the same inclusive conclusions we still have now. I was hoping for a little more in-depth treatment of the subject, similar to the (superior) Mars version of this book.
Ah well - I laughed, I cried, I kissed six bucks goodbye. There's a lot more stuff in this booklet though, so it was still a good buy.


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Rick Woods
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Re: Ashen Light - Redux new [Re: Rick Woods]
      #5815408 - 04/22/13 02:20 PM

I found an interesting article from 1970 in the JBAA by D.S. Brown titled "The Ashen Light - A Refraction Effect?" in which the author makes a good case for the AL being caused by light refracted around from the daylight side by the dense atmosphere. This seems very plausible to me. So does Fred Taylor's theory of the glowing red surface being visible sometimes through thin spots in the cloud cover. Evidently the auroral activity is considered unlikely because of the weak magnetic field of Venus.

Another article cites a German astrophotographer who imaged the AL in ultraviolet at the same time an observer was reporting it cisually through a blue filter.

Still another suggests lightning, as considerable evidence of lightning has been seen by spacecraft, and displays a preference for the evening side of Venus as opposed to the morning; the visual record mirrors this preference, but may be due to people preferring to observe in the evening instead of the morning.

My vote right now is for refraction; glowing surface runs second.


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GlennLeDrew
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Re: Ashen Light - Redux new [Re: Rick Woods]
      #5817586 - 04/23/13 02:06 PM

How high are the cloud tops? If at sufficient altitude, the clear atmosphere above will not have a particularly high density. That notwithstanding, would it not be a most astonishing coincidence that the refraction should be just so, in order to maintain a near constant level of illumination all the way to the anti-solar point on the globe? And if the atmosphere is dense enough to so strongly bend the light yet not attenuate it to any appreciable degree, implies an almost magical degree of transparency. To be so transparent over such long distances yet at the same time scatter light to the point of ready visibility is an obvious incongruity.

Such a degree of scattering can only occur with a significant degree of attenuation--after all, the scattered light is being 'removed' from continued direct propagation. In such case, any ashen light so resulting should be seen only as a glow confined to the terminator region, decreasing in surface brightness toward the anti-solar point, probably dimming to invisibility (against the other illumination from external sources) after perhaps some 5-10 degrees (several hundred to *maybe* 1,000 km) into the night side.

Edited by GlennLeDrew (04/23/13 02:19 PM)


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azure1961p
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Re: Ashen Light - Redux new [Re: GlennLeDrew]
      #5817801 - 04/23/13 03:31 PM

You know what's more compelling to me here if I could sidetrack a moment - when the crescent is ultra thin and the terminator particularly toward the cusps begin to reveal the patchy cloud topography. Glenn mentioning the glow beyond the terminator on an example and it merely made me think of another cloud phenomenon.

Ok back to scheduled programming.

Pete

Edited by azure1961p (04/23/13 03:32 PM)


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Rick Woods
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Re: Ashen Light - Redux new [Re: GlennLeDrew]
      #5818168 - 04/23/13 06:00 PM

Quote:

How high are the cloud tops? If at sufficient altitude, the clear atmosphere above will not have a particularly high density.




Glenn,

The easiest answer I could find without lots of digging was from Patrick Moore ("Venus", 2002, p.151):

"There are various cloud layers. The upper clouds lie at around 43 miles above ground level; the cloud deck ends at 18 miles above the surface, and below this the visibility is unexpectedly good..."

Does this tell you anything?


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David Knisely
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Re: Ashen Light - Redux new [Re: ROBERT FREE]
      #5819743 - 04/24/13 12:58 PM

Quote:

ive seen it a few times myself over the years,but sometimes i think the brain causes some of it ,but patrick moore has also stated he an other good astronomers saw that as well.in daylight when the crescent is real big i saw it a few times over the years and the surface area was definitely darker on venus opposite the crescent.




Well, very very near inferior conjunction with Venus as narrow a crescent as it can get, there is light scattered by the atmosphere of Venus that will sort of "complete the circle" of the entire edge of the disk of the planet (and may be visible and recordable in daylight observations), but this is not the Ashen light. The Ashen light is quite faint and is reportedly seen on the un-illuminated disk of Venus under darker sky conditions with a planetary phase that is not as strongly crescent as the inferior conjunction is and is also seen away from the limb of the planet. I have never seen it, but it may be a variable phenomena. To my knowledge, it has never been imaged and there isn't much hard evidence for its existence. Clear skies to you.


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GlennLeDrew
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Re: Ashen Light - Redux new [Re: David Knisely]
      #5820524 - 04/24/13 07:06 PM

Rick,
At an altitude of 50 km or so, Venus's atmospheric pressure is much like that at sea level on earth. At the cloud tops of 43 km, the air pressure would be a big greater than at sea level on Earth. Our atmosphere refracts light at sea level by just over 1/2 degree. At cloud top level on Venus, then, we might assume a refraction of about a degree.

A check on this is afforded by the observation of the completion of the atmospheric ring of light around the full disk when very near inferior conjunction. The elongation of the planet from the Sun st that time tells us that this is angle light is refracted into the night side.


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Rick Woods
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Re: Ashen Light - Redux new [Re: GlennLeDrew]
      #5822242 - 04/25/13 01:52 PM

Glenn,

That was 43 miles, not kilometers.
Also, you'd have to consider the density, constitution, and conditions of the atmosphere. The AL isn't always there; there must be conditions that occur periodically that make it visible.


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Rick Woods
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Re: Ashen Light - Redux new [Re: Rick Woods]
      #5832398 - 04/30/13 01:52 PM

In the now-locked "Spokes on Saturn's Rings" thread, one member made the comment in passing that the AL had indeed been imaged in visible light. That was, of course, a minor bombshell to drop; and several of us encouraged him to provide, or point us at, some documentation of it here in this thread. I also PM'd him with this request.
So far, no response has been forthcoming; so much as I'd love to see such an image, I think we're back to the "never been imaged" point.

Rats!


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