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Ashen Light - Redux

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#151 GlennLeDrew

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Posted 02 April 2013 - 02:45 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.

#152 stanislas-jean

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Posted 02 April 2013 - 05:40 AM

Scotopic, this might be, not in mesopic mode.
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#153 stanislas-jean

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Posted 02 April 2013 - 06:04 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

#154 Rick Woods

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Posted 05 April 2013 - 02:21 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.

#155 Edward E

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Posted 05 April 2013 - 10:39 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.

#156 Rick Woods

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Posted 05 April 2013 - 12:51 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.

#157 stanislas-jean

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Posted 05 April 2013 - 12:56 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

#158 buddyjesus

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Posted 05 April 2013 - 01:39 PM

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

#159 buddyjesus

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Posted 05 April 2013 - 01:41 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.

#160 Edward E

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Posted 05 April 2013 - 02:29 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.

#161 starbux

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Posted 05 April 2013 - 02:38 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.

#162 brianb11213

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Posted 05 April 2013 - 03:23 PM

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.

#163 GlennLeDrew

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Posted 05 April 2013 - 06:14 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.)

#164 azure1961p

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Posted 05 April 2013 - 07:38 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.

.


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

#165 azure1961p

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Posted 05 April 2013 - 07:40 PM

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

#166 stanislas-jean

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Posted 06 April 2013 - 07:24 AM

I think the alert procedure would be usefull for confirmation or not a confirmation.
A good way for cross checking results.
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#167 stanislas-jean

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Posted 06 April 2013 - 07:27 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.
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#168 BillFerris

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Posted 06 April 2013 - 10:15 AM

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.

#169 stanislas-jean

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Posted 06 April 2013 - 12:13 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.
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#170 Rick Woods

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Posted 06 April 2013 - 01:14 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.

.


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.)

#171 Rick Woods

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Posted 06 April 2013 - 01:23 PM


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. :) )

#172 Rick Woods

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Posted 06 April 2013 - 01:30 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.


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.

#173 GlennLeDrew

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Posted 06 April 2013 - 01:46 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.

#174 azure1961p

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Posted 06 April 2013 - 04:11 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

#175 Rick Woods

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Posted 06 April 2013 - 06:30 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.


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.

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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