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stanislas-jean
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Reged: 10/22/08

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 hypothÚsis (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
Imaging Editor - Sky & Telescope
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Reged: 01/22/07

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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
Imaging Editor - Sky & Telescope
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Reged: 01/22/07

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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
Carpal Tunnel


Reged: 10/22/08

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
Carpal Tunnel


Reged: 10/22/08

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
Carpal Tunnel


Reged: 10/22/08

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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stanislas-jean
Carpal Tunnel


Reged: 10/22/08

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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Reged: 07/07/10

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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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buddyjesus
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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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Reged: 03/26/06

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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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