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Global True Color View Of Venus?
scalbers
post Mar 25 2017, 02:55 PM
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QUOTE (DonPMitchell @ May 5 2006, 08:49 PM) *
There is a spectral albedo for Venus. That can be turned into XYZ, via the CIE tables. Then convert that into Standard RGB ("sRGB"), which is a set of phosphor chromas that the computer industry and the HDTV people all more or less agree on. It has a gamma of 2.2.

Here's a set of planet colors, with brightnesses proportional to the total albedo:Planetary Palette


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.


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JRehling
post Mar 26 2017, 10:12 PM
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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.

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JRehling
post Jun 11 2017, 05:59 PM
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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
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JohnVV
post Jun 11 2017, 06:32 PM
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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
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JRehling
post Yesterday, 05:20 AM
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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.
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