Return to the Cloudy Nights Telescope Reviews home page


Observing >> Solar System Observing

Pages: 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 | 11 | (show all)
buddyjesus
Carpal Tunnel
*****

Reged: 07/07/10

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

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

Post Extras: Print Post   Remind Me!   Notify Moderator  
stanislas-jean
Carpal Tunnel


Reged: 10/22/08

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

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

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


Post Extras: Print Post   Remind Me!   Notify Moderator  
buddyjesus
Carpal Tunnel
*****

Reged: 07/07/10

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

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

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


Post Extras: Print Post   Remind Me!   Notify Moderator  
stanislas-jean
Carpal Tunnel


Reged: 10/22/08

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

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


Post Extras: Print Post   Remind Me!   Notify Moderator  
David Gray
sage
*****

Reged: 08/06/12

Loc: Co. Durham UK
Re: Ashen Light - Redux new [Re: azure1961p]
      #5755566 - 03/25/13 06:48 AM

Quote:

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

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

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

Pete




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

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

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

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


Post Extras: Print Post   Remind Me!   Notify Moderator  
Scanning4Comets
Markus
*****

Reged: 12/26/04

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

I've seen it also!

Post Extras: Print Post   Remind Me!   Notify Moderator  
photonovore
Moonatic
*****

Reged: 12/24/04

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

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

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

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

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




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

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

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


Post Extras: Print Post   Remind Me!   Notify Moderator  
GlennLeDrew
Postmaster
*****

Reged: 06/18/08

Loc: Ottawa, Ontario, Canada
Re: Ashen Light - Redux new [Re: photonovore]
      #5758809 - 03/26/13 06:26 PM

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

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

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

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

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

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


Post Extras: Print Post   Remind Me!   Notify Moderator  
azure1961p
Postmaster
*****

Reged: 01/17/09

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

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

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

Pete


Post Extras: Print Post   Remind Me!   Notify Moderator  
Rick Woods
Postmaster
*****

Reged: 01/27/05

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

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

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

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


Post Extras: Print Post   Remind Me!   Notify Moderator  
stanislas-jean
Carpal Tunnel


Reged: 10/22/08

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

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

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

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


Post Extras: Print Post   Remind Me!   Notify Moderator  
GlennLeDrew
Postmaster
*****

Reged: 06/18/08

Loc: Ottawa, Ontario, Canada
Re: Ashen Light - Redux new [Re: stanislas-jean]
      #5759625 - 03/27/13 06:29 AM

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

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

Let's break it down.

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

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

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

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

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

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


Post Extras: Print Post   Remind Me!   Notify Moderator  
azure1961p
Postmaster
*****

Reged: 01/17/09

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

Rick,

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

Pete


Post Extras: Print Post   Remind Me!   Notify Moderator  
stanislas-jean
Carpal Tunnel


Reged: 10/22/08

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

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


Post Extras: Print Post   Remind Me!   Notify Moderator  
stanislas-jean
Carpal Tunnel


Reged: 10/22/08

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

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


Post Extras: Print Post   Remind Me!   Notify Moderator  
GlennLeDrew
Postmaster
*****

Reged: 06/18/08

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

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

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

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

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

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

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

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


Post Extras: Print Post   Remind Me!   Notify Moderator  
azure1961p
Postmaster
*****

Reged: 01/17/09

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

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

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

Pete


Post Extras: Print Post   Remind Me!   Notify Moderator  
GlennLeDrew
Postmaster
*****

Reged: 06/18/08

Loc: Ottawa, Ontario, Canada
Re: Ashen Light - Redux new [Re: azure1961p]
      #5761285 - 03/27/13 08:52 PM

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

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


Post Extras: Print Post   Remind Me!   Notify Moderator  
azure1961p
Postmaster
*****

Reged: 01/17/09

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

Ill have a look thanks for the heads up.

Pete


Post Extras: Print Post   Remind Me!   Notify Moderator  
stanislas-jean
Carpal Tunnel


Reged: 10/22/08

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

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


Post Extras: Print Post   Remind Me!   Notify Moderator  
Pages: 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 | 11 | (show all)


Extra information
2 registered and 5 anonymous users are browsing this forum.

Moderator:  Rich (RLTYS), star drop, Mitchell Duke 

Print Thread

Forum Permissions
      You cannot start new topics
      You cannot reply to topics
      HTML is disabled
      UBBCode is enabled


Thread views: 7518

Jump to

CN Forums Home




Cloudy Nights Sponsor: Astronomics