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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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brianb11213
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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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azure1961p
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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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stanislas-jean
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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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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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BillFerris
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Re: Ashen Light - Redux [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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stanislas-jean
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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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Rick Woods
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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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Rick Woods
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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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Rick Woods
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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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GlennLeDrew
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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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azure1961p
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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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Rick Woods
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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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Rick Woods
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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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brianb11213
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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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stanislas-jean
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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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GlennLeDrew
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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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GlennLeDrew
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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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