It's not merely about color, it's about contrast. And quite frankly, in visible wavelengths there just isn't any appreciable contrast.

Yes indeed the actual contrast is much more subtle than in the Pioneer UV images. For example Ricardo Nune's images show Venus Express processed into approximate RGB, showing rather subtle hues. This procedure might be applied to the Pioneer UV images perhaps, even though these are monochromatic. It's kind of interesting to me to consider whether the human eye can perceive at least some faint contrast/color with Venus. Perhaps it relates to violet light sensitivity that can vary between individuals.

I haven't found too many spectra of Venus or its cloud features. Here is a VIMS spectrum of Venus for reference, though I'm unsure of the field of view.

http://vims.artov.rm.cnr.it/data/res-ven.html

More discussion is here:

http://www.unmannedspaceflight.com/index.p...amp;#entry20237

Here is a book excerpt showing illustrations of visual observations of Venus' clouds, so the contrast is detectable to some, seen right here from planet Earth:

http://books.google.com/books?id=LqwUuMYIE...ope&f=false

Has anyone actually tried to make a true-colour map of Venus' surface directly from the Magellan radar data? I know there's separate topo data available but IIRC that was pretty low resolution - is it possible to extract data directly from the SAR images (e.g. pulse travel time) to get higher-res altimetry? And then make a global topography map from that, coloured as if we were looking at basalts?

I don't know how you could ever make a 'true color' map of the surface of Venus. We've only seen a very few small spots from the Venera probes--not enough to generalize about the entire planet--and there's no way to extract color from radar data. If that wasn't enough, lighting conditions, surface compositions, etc. undoubtedly do vary for a variety of reasons, so even if we could somehow obtain visible-light surface images of the entire surface that wouldn't necessarily correspond with what the human eye would actually see.

Even doing this for Mars is a formidable challenge; there's inevitably some degree of interpolation/assumption involved, as our resident imagemages will surely attest.

My personal experience is positive. I can see "something" on Venus through a telescope. My best description would be of a white crescent with some brighter parts. Those bright spots look slightly fluorescent. But it's not obvious, the contrast is very subtle and there's no color at all. Like looking at snow deposited over snow.

I think it has to do with the Rod cells on our eyes. Those are most sensitive to wavelengths of light around 498 nm and are responsable for the Purkinje effect http://en.wikipedia.org/wiki/Purkinje_effect. Perhaps something like that works for Venus.

Well, it'd definitely be "simulated true colour". I was thinking more "this is what the surface could look like, assuming basaltic composition". I know that bright (reflective) radar patches aren't necessarily bright in visible light, for example - they're just rough surface (unless they're on mountaintops IIRC, in which case they might actually be pyrite deposits?).

Someone could take a small feature on Venus (e.g. a dome or crater) and translate the radar bright/dark into visible (using appropriate rules like "radar bright = rough surface, radar dark = smooth surface") that would be nice. I guess it's more a space art/visualisation thing than anything "scientific", but it'd be nice to be able to look at a view of Venus and say "that's what we might see if we looked at this feature in visible light".

How on earth would that be any less simulated than one based on the Venera pictures?

Pretty neat that you've been able to see such features. It seems to me Venus is bright enough so it would work more with cones rather than rods.

While color may not show up with a small crescent, I can speculate that if one can see features from Earth, then orbiting in a spacecraft it would look large enough to have a chance at seeing a slight hue.

I dunno, I didn't say it would be

true color - not possible
now a "better" than that old red/orange and yellow/white
http://photojournal.jpl.nasa.gov/jpegMod/PIA00481_modest.jpg
http://photojournal.jpl.nasa.gov/jpegMod/PIA00104_modest.jpg

the color i settled on
http://www.unmannedspaceflight.com/index.p...st&p=164503

now as to clouds
They change SO fast that there is no "real" up to date data
-- artist concept --

that i use a 100% artistic map for it
a link to a artistic thread
http://www.shatters.net/forum/viewtopic.php?f=5&t=16019
( the last post is the above image)

the color is adjusted so that some of the clouds can be seen and it looks like "bright smog"
basically it is darker than if "you" were in orbit looking down at it

I came across Don Mitchell's page, so the RGB values could indeed be calculated for Venus (sky) as seen from space and from the Venusian surface.

It's interesting that Rayleigh scattering from CO2 is somewhat competitive with the scattering of light by the clouds. Only 2.5% absorption by clouds as well in visible light.

A long-dormant thread awakens!

I think one thing is clear: If a person orbiting Venus looked down at the clouds, the sensation would probably be pain. It hurts to look at white snow on a sunny day and Venus is similar but twice as bright. It would have an overwhelming brilliance that would require some sort of filtering – sunglasses – for a person to have a chance at perceiving it without saturation of the cones. And once you're filtering, "real" goes out the window.

We could employ neutral filters that damp down every wavelength equally, but the psychophysical research says that the degree of damping affects the perceived color (i.e., the Purkinje Effect). So now we're once again into the realm of the subjective.

Over the past few months, I've looked at Venus more often than any other year. Sometimes at night, but often in the day, seeing its gibbous and crescent forms in a blue daytime sky, including yesterday when I saw it at inferior conjunction – north of the Sun, appearing neither in the evening nor morning, with its southern crescent lit. I've looked at it at least ten times since early December. In the daytime blue sky, Venus looks white – the same white as a front lit cumulus cloud. In a dark sky, I have felt like there are hints of color, but they're right at the threshold of perceptibility and, moreover, the atmospheric conditions on Earth may introduce a bigger color signal than whatever is on Venus itself.

Here's an interesting look at the empirical facts, from Venus Express:

https://www.researchgate.net/profile/Santia...spectrum-in.png

The top panel shows that Venus' spectrum is sloped very slightly towards the blue over most of the visible range, but then it begins to fall off steeply in reflectance into the violet. In essence, Venus is not spectrally neutral but the short, steep decline in violet is offset by the long, gradual excess blue relative to the longer wavelengths. But this empirical data is only as meaningful as our ability to translate it in terms of perception and there we get into the murkiness of human color vision, phase angle, etc.

In summary, Venus appears almost painfully, brilliantly white. In conditions when lenses, mirrors, or filters decrease the intensity, it's still very close to white with an excess of blue and a deficit of violet perhaps canceling out, but what is perceived will depend upon context.

This video not only has a nice overview of the Akatsuki mission, but also has a nice global view of Venus at around 1:20. I have no idea what produced this image, but it looks right to me. Quite similar to the view I made by taking my own photos of a gibbous Venus, projecting them onto a map, filling in the gaps assuming perfect symmetry, and then projecting that map onto a sphere for the "full" Venus view.

https://www.youtube.com/watch?v=NP1q_Kl-y74

some guesses
at 1:15 i would say venus express
at 1:28 that is the orange megllian radar data
at 1:31 pioneer venus

This may be about as good as you can get from Earth for a true-color photo of Venus in a full phase. Taken by amateur Arnaud van Kranenburg back in 2006 as part of the amateur campaign to assist Venus Express. The leftmost image in the second row is RGB, and seems close to true color, and Venus is 98% full. If you wanted to "convert" this to 100% full, it would do pretty well to copy the right limb and reflect it over the left side, which features the almost-full terminator.

http://sci.esa.int/venus-express/40018-vaop-images/

What's lacking is resolution – Venus was on the far side of the Sun and the instrument was only a 9.25-inch telescope. However, since there is likely next to no discernible detail to be had at higher resolution, it's not too hard to upscale + blur (+ deconvolve) this into a very good simulation of what the same view at higher resolutions would resemble.