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Thread: The Many Faces of Venus

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    The Many Faces of Venus

    As your heliochromologist (wink) it should be obvious that the "true" colors of the planets are due to the Sun's light. Thus the many wonderful and bizarre color portrayals of our nearest neighboring planet, Venus, should interest us and I'm one who's justified in presenting it. [Pause for beating chest and eating yellow Sun-ripe banana.]

    A few years ago I searched fairly hard to find a "natural color" rendering for Venus. Given its brightness and proximity, I was a bit surprised. I found some serious work by Richard Nunes (?) that seemed reasonable, certainly far better than the traditional red radar renditions. His work, and others perhaps since his work, seem to use the Mariner 10 images, but these seem to be taken from an orange and a UV filter, thus limited in not only a true-color result but the greater emphasis from UV of clouds would be difficult, I think, to take into account.

    Many sites because they are science-based state that the images use false coloring. But you might be surprised how many of them don't bother.

    The Messenger image, however, uses red, green, and blue filters, apparently, and would seem to be ideal for something close to a true color rendering. I found it at the Planetary Society.

    Planetary Soc RGB image.jpg

    For fun and to see just how often the color variations for Venus are on the internet, I entered "planet Venus" into the Google machine to see what came out. I was curious how many sites I would find before getting to one that had it "right". I gave up after 75. You might enjoy what has been represented for the "planet Venus". I entered the goddess(?) -- on page 2 -- because her color is far more accurate than most.

    Venus colors 1 of 3.jpg

    To see the images of each site, simply do the Google search for "planet Venus". They are done in order and shown using the three-column format.

    [two more to follow]
    Last edited by George; 2018-Jul-12 at 08:19 PM.
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    Next page.

    Venus colors 2 of 3.jpg


    BTW, if I were to grade them on any of their choice for the Sun's color, guess what it would be?

    Perhaps 10 years or so from now, we can come back here and note how much more accurate the sites become for both the Sun, which has been improving, and for Venus. The other planets are sitting nicely, I think.
    Last edited by George; 2018-Jul-13 at 02:44 PM.
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    Last edited by George; 2018-Jul-13 at 07:26 PM.
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    Quote Originally Posted by George View Post
    Last page...

    Attachment 23451
    Your attachments are giving me "invalid attachment" messages.

    As a reflector, we can define true color by means of the difference between the incident and reflected light. My old Norton's Star Atlas gives its color index as about 1.2, similar to a K star. If attenuated for comfort it should look very pale yellowish white or pale beige if the Sun is dominating our ambient light.

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    Quote Originally Posted by Hornblower View Post
    Your attachments are giving me "invalid attachment" messages.
    This is my second attempt to fix it. I assume that the file sizes are a bit large (~750k), which is kinda necessary to show so many different images. When I first post them, they are fine but something happens and they won't work.

    It seems that only page 3 needed correction, which I have edited. Are they working now?

    As a reflector, we can define true color by means of the difference between the incident and reflected light. My old Norton's Star Atlas gives its color index as about 1.2, similar to a K star. If attenuated for comfort it should look very pale yellowish white or pale beige if the Sun is dominating our ambient light.
    Why are you thinking like an astronomer? Oh yeah, ok.

    Since color is strictly an eye/brain perception, my preference for a "true color" or "natural color" definition would be what an object simply looks like to the human eye as we would normally see it. This would be for the up close and personal (extended) views of these objects. That's what we see every day, but that's after atmospheric extinctions of sunlight, admittedly. I don't know that we have ever tackled it, but the reduction in the blue-end of the spectrum by our atmosphere could potentially cause objects that we would see from a spaceship might look a little more blue than with a quality reflector from Earth. My guess is that it would not make any difference more often than not. The photon flux distribution, as we have talked about in the past, is remarkably flat for an AM0 sp. irr. and I suspect the eye might see this as an almost perfect white standard. [That's speculation on my part, of course.] Also, color constancy is quite powerful and the eye is quick to recalibrate in order to render true color unless the incident light spectrum is highly altered.

    Another way to put it would be what an object (eg planet) looks like if we go there and take quality pictures of it, or if we go there and shrink it then bring it back with us and put it in the Smithsonian, but with quality lighting upon it of course. I doubt we would see much difference.

    For Venus, the subtle difference we see between the Mariner "natural color" attempt and the Messenger attempt are notable but trivial when we consider all the bizarre colors chosen for it as I demonstrate, most of which don't bother to mention that they are false color images. They seem content to regurgitate that red radar image year after year. But, I don't want to be overly critical since we all need a little artistic touch now and then, especially for a vanilla white Sun. [Don't tell anyone I said that, of course..]
    Last edited by George; 2018-Jul-13 at 07:52 PM.
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    This is pretty amazing. I had thought Venus would look like a white ball with a pale yellow wash, if I were to look right at it from a few hundred km away. Now that I think about it, the shield over my helmet or the glass in the spacecraft window might add additional tints, so I would never really know.

    It makes me think of the difficulty in correctly reproducing color using photography on Earth, having to reduce the amount of blue to get them to look "right".

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    This is how a setting Venus looked to me a month or so ago.... bright!

    hhr089.jpg
    Everyone is entitled to his own opinion, but not his own facts.

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    This isn't concerning Venus, but is Mars almost due west in the evening sky around 2100 CDT?

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    Quote Originally Posted by Roger E. Moore View Post
    This is pretty amazing. I had thought Venus would look like a white ball with a pale yellow wash, if I were to look right at it from a few hundred km away.
    A few hundred km might be close enough to see subtle streaks of pale yellow or some other color. But a few ten thousand km, I suspect the R/G/B filtered image result might be accurate. That doesn't mean a pale yellow is ruled-out, necessarily, however. Hornblower's reference would favor a yellowish color, but I don't know if that Star Atlas adjusts for our atmospheric extinctions, though I doubt it.

    Now that I think about it, the shield over my helmet or the glass in the spacecraft window might add additional tints, so I would never really know.
    It's unlikely, IMO, that in the case of a white or almost white object that is as bright as Venus would be affected by small amounts of extinctions due to nearly neutral glass. The retinex (eye-brain system) has a powerful color constancy ability to make near-white objects be seen as white, which allows the brain to render near true-color results for all objects that reflect this light source. [One example is to look at a car lamp (older tungsten class) at night and compare it to it seen during bright daylight. The difference is striking. The brain will make the night view of it much whiter.]

    It makes me think of the difficulty in correctly reproducing color using photography on Earth, having to reduce the amount of blue to get them to look "right".
    This is especially true for the lower altitude angles where extinctions are extensive, especially on the blue end, which is why we can sometimes see the solar disk comfortably. In this case, the Sun will necessarily appear yellowish-orange or redder than this.

    A few years ago, The Heliochromologist invented the asterochromograph that alters the spectrum through a prism to make the necessary corrections for atmospheric extinctions. The spectrum is recombined and homogenized (scrambled) to form a bright spot. This allows the eye to actually see its true color. A spectrometer can be used to confirm its match to the spectral results from astronomers. A proto-type was made but never finished due to the lack of clout afforded all known heliochromologists on the planet, though not undeservedly, admittedly. *wink*
    Last edited by George; 2018-Jul-25 at 07:09 PM.
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    Quote Originally Posted by Cougar View Post
    This is how a setting Venus looked to me a month or so ago.... bright!

    hhr089.jpg
    Nice! She looks like a goddess for some reason!
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    Quote Originally Posted by bknight View Post
    This isn't concerning Venus, but is Mars almost due west in the evening sky around 2100 CDT?
    That is Venus. Mars is in the East. [You might want to get, for free, Stellarium.] Venus is bright white, always, and Mars orangish, more orange when near the horizon, of course.
    Last edited by George; 2018-Jul-25 at 07:07 PM.
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    Quote Originally Posted by Hornblower View Post
    Your attachments are giving me "invalid attachment" messages.

    As a reflector, we can define true color by means of the difference between the incident and reflected light. My old Norton's Star Atlas gives its color index as about 1.2, similar to a K star. If attenuated for comfort it should look very pale yellowish white or pale beige if the Sun is dominating our ambient light.
    A big "oops!" on my part. That color index of 1.2 is for the Moon. Venus is listed as 0.91 as compared with the Sun at 0.72 and Vega, the standard chosen as neutral in this system, as 0.0. That yellowing or reddening with respect to the Sun is so slight that my guess is that it would look neutral white in a flyby with the Sun as the ambient light. The B-V color index does not give enough information to tell whether the pastel tint would be yellow, orange, or perhaps a shade of pink. All it tells us is that the blue band is somewhat diminished compared with the fat part of the spectrum. We would need a high resolution spectrometer such as what George described. For evaluating a reflective color we could do just fine here on the ground, comparing Venus and the Sun side by side.

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    Quote Originally Posted by Hornblower View Post
    A big "oops!" on my part. That color index of 1.2 is for the Moon.
    Ah that helps.

    Venus is listed as 0.91 as compared with the Sun at 0.72...
    There seems to be a range of values for the color index for Venus. Kuiper, here (3rd paragraph), uses 0.8 but he also quotes Danjon's value of 1.0. Perhaps 0.9 is a good average. It also mentions that there is difficulty deriving the color index, which seems ironic given its brightness. Is this because it is and extended objected and, perhaps, an irradiance measurement is needed but may be too faint for past instruments that conducted B-V tests?

    Elsewhere I found that Kuiper called Venus "slightly yellowish" but that "most observers classify the planet as white rather than yellow."

    Also, isn't the Sun 0.65?

    We would need a high resolution spectrometer such as what George described.
    Well… I believe the ultimate “true color” determination would be best in seeing an actual spot of color. Once we have a likely true color spot, then a spectrometer could be used to verify its results with that of the target object to see that both SEDs match.

    The Asterochromograph was designed to do this very thing. (attached)

    Asterochromograph.jpg
    Last edited by George; 2018-Jul-27 at 03:23 PM.
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    Here is a less rushed and less grammatically bungled attempt...

    Asterochromograph b.jpg

    P.S... A prototype was made for the purpose of adding greater evidence of the Sun's true color (as seen above our atmosphere). Once it was obvious that a mere solar projection is all that is needed to falsify any tint of yellow for the Sun, the heliochromograph became "too much squeeze for the juice." However, given astronomer's great advancement with exoplanets, perhaps this instrument would serve to produce the most accurate true color for exoplanets. Would it not?
    Last edited by George; 2018-Jul-27 at 03:50 PM.
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  15. 2018-Jul-27, 03:43 PM
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