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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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buddyjesus
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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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buddyjesus
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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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stanislas-jean
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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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David Gray
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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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David Gray
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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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buddyjesus
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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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buddyjesus
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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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azure1961p
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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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stanislas-jean
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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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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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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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azure1961p
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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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stanislas-jean
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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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David Gray
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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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azure1961p
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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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buddyjesus
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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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