Venus Again!

[BobHegwood]

I know that we've been over this a hundred times, but I am really becoming frustrated with the lack of an answer (which I can believe) to the following question:

"What does the surface of Venus look like in TRUE colors?"

Here is a post of the best (obviously re-processed) image that I have been able to find. I still have problems in trying to decide what the surface of Venus looks like to the naked eye though, mainly because the lower image has basically removed the effects caused by Venus' atmosphere. Let me ask this same, tired, stupid question again in another way...



If someone alive knows the exact colors of the tab protruding from the Venera spacecraft, then WHY cannot the TRUE colors of Venus' surface be approximated correctly, and including the atmospheric effects on the colors we would see with eyeballs?

Damned frustrating...

[t00fri]

Bob,

this subject including these two crucial Venus images have been discussed by me several times extensively in the past.

The last public discussion was here (1.5 years ago), I believe.
viewtopic.php?f=10&t=10611

Cheers,
Fridger

[BobHegwood]

Bob,

this subject including these two crucial Venus images have been discussed by me several times extensively in the past.

The last public discussion was here (1.5 years ago), I believe.
viewtopic.php?f=10&t=10611

Cheers,
Fridger

Sorry Fridger...
I did indeed execute a variety of searches within the forum, but have apparently not the skill it takes to execute one correctly. I tried using [+Venus +surface +color] but - as usual - I simply do NOT know what the Hell I'm doing.

Thanks for the link.

[BobHegwood]

So let's see if I get the gist of what you and Chris were referring to...

Chris wrote:

I agree completely, and in fact have created a version of the code that used the filtered color for the *specular* light. This produced a very nice effect of orange reflections on water during sunrises and sunsets. For diffuse light, the results seemed strange for the familiar case of the Earth. The color shift seemed too dramatic--I don't think I was properly accounting for the contributions of the direct light from the Sun and the scattered light from the sky.

So from this bare minimum of information, can I assume that one can account for the atmospheric effects on Venus using some sort of specular color map?

Sorry, I know I'm a real pain in the Wazoo, but I am really trying to understand the situation with Venus here. In fact, I have been for about two months now. Ask John van Vliet. He'll tell you what a real pain I can be.

I really am sorry here, but I simply fail to see how Venus can be rendered as a gray scale image when there is so much activity apparent on its surface. The very high temperatures, the existence of calderas, lava plains, trenches, etc. just simply do not allow me to believe that we'd see a gray surface if we could walk around on Venus.

[The Singing Badger]

But lava IS grey, isn't it? (When it hardens.)

[Grasping at limits of my geological knowledge here...]

[BobHegwood]

But lava IS grey, isn't it? (When it hardens.)

[Grasping at limits of my geological knowledge here...]

Depends on its chemical composition (and how it was formed) doesn't it? I'm not saying that you wouldn't see grey in the landscape.
It's just that I think (from lots of research) that there would also be orange and brown colors involved here. Some
of this would be due to the environment itself, and some of it would be due to the makeup of the surface. Of course, since I really
don't know what the Hell I'm doing here, I suppose that it could be any color you like.
I have found resources which do agree, however, with my current uneducated assessment of the colors involved in the surface
of Venus. This is what is so confusing though... One site says one thing and another site says another thing. Even the "experts"
do not agree.

Thanks, Bob

[ajtribick]

Well lava typically is grey after it forms (particularly basaltic lava, which is probably what we're looking at on Venus), however what subsequent weathering in the Venusian environment would do to it, I don't know.

Another question is about the texture we are using for the clouds - is it too yellow? My general impression is that the Venusian cloudtops are pretty much white with a slight yellowish tint...

[BobHegwood]

Well lava typically is grey after it forms (particularly basaltic lava, which is probably what we're looking at on Venus), however what subsequent weathering in the Venusian environment would do to it, I don't know.

And I have seen samples of basaltic rock which are anything BUT grey. Sorry, but I do not recall if these were lava samples though. Please forgive my obvious confusion here.

Another question is about the texture we are using for the clouds - is it too yellow? My general impression is that the Venusian cloudtops are pretty much white with a slight yellowish tint...

I would agree here. Most (or all) of the cloud textures we have are old, and from a single photo of a "piece" of the atmosphere which has been replicated across the entire surface of Venus.

[ANDREA]

But lava IS grey, isn't it? (When it hardens.)

Surely it is, as we can see in the following images, from all over the world:
Hawaii:

Hawaii:

Iceland:

Mt. Etna, Sicily, Italy:


If we exclude the sky, some poor vegetation and a slight bluish tint due to the images poor quality, in these images grey and dark gray are the lords of lava fields colors.
Sincerely I don't understand why Bob cannot accept that on Venus the colors can probably be the same dull greys.
Bye

Andrea

[BobHegwood]

If we exclude the sky, some poor vegetation and a slight bluish tint due to the images poor quality, in these images grey and dark gray are the lords of lava fields colors.
Sincerely I don't understand why Bob cannot accept that on Venus the colors can probably be the same dull greys.

Simply because of the atmospheric effects on that landscape (sulfuric acid rain, and the atmosphere itself on our vision). That's all.
I'll go away now. Thanks for the information though.

EDIT: See here for more reasons for confusion. And see HERE where the surface is described as:

In 1982 Veneras 13 and 14 proved especially lucky, returning the first color pictures of the surface of Venus immediately surrounding the landers, showing orange-brown rocks and soil.

Finally, there is every indication that there are vast quantities of Iron Pyrite available on the surface of the planet. Iron Pyrite is anything but gray. Does my confusion here make more sense now?

Of course, the Moon is absolutely grey too, right? If that's the case though, how did the astronauts find Orange Soil?

[bdm]

Well lava typically is grey after it forms (particularly basaltic lava, which is probably what we're looking at on Venus), however what subsequent weathering in the Venusian environment would do to it, I don't know.

Another question is about the texture we are using for the clouds - is it too yellow? My general impression is that the Venusian cloudtops are pretty much white with a slight yellowish tint...

Yes, the cloud tops are basically white.

The cloud bottoms are a whole different kettle of fish. Remember there is 90 atmospheres of pressure there. This means there's a lot of molecules available to scatter the light. The sky of Venus is yellowish due to the high pressure. This is evident in the pictures that Bob posted.

Here is a discussion on sky colour that may be useful: http://www.orionsarm.com/whitepapers/sk ... orlds.html

[ajtribick]

I would have guessed the colour visible at the bottom of the atmosphere was due to lots of scattering rather than the absolute pressure...

Out of interest, is it known where the sun was with respect to the horizon when the Venera picture was taken?

[bdm]

I would have guessed the colour visible at the bottom of the atmosphere was due to lots of scattering rather than the absolute pressure...

Indeed - and the high pressure is the cause of the scattering.

[t00fri]

The sky of Venus is yellowish due to the high pressure. This is evident in the pictures that Bob posted.

In general, the sky color is indeed the result of the multiple scattering of light on molecules and aerosols in the atmosphere. Theoretically the scattering is described by the so-called Mie theory and depends on a number of parameters! Firstly, there is the density of molecules and aerosols that varies exponentially with altitude. Another crucial ingredient are the sizes of the scattering particles! Mie scattering in the limit of small sizes is the familiar Rayleigh scattering, the scattered intensity of which varies like ~1/wavelength^4. For large aerosols (dust...) the characteristics of Mie scattering are becoming completely different. Then there are the various components of optical scattering the relative importance of which again depends on the properties of the particles: absorption, reflection etc. Last not least it depends on the relationship of the sun's position relative to the viewing direction...

In any case the resulting sky color is due to a number of wavelength dependent components of the general Mie scattering theory.

Because of these complex dependences, the sky color can adopt a variety of shades on different celestial bodies, e.g like so:

Earth





Venus


Mars



Titan

Here is a discussion on sky colour that may be useful: http://www.orionsarm.com/whitepapers/sk ... orlds.html

Here is a discussion on sky colour that may be useful : http://forum.celestialmatters.org/viewt ... 16&start=0

Fridger