Colorful Easter hunt challenge to all

[George]

Being Easter, perhaps, I feel a little more colorful than normal.

Who wants a free ice cream Sundae?

Be the first to present a public mosaic of our Solar system that is color correct, and I'll treat you to an ice cream Sundae!

I only require the natural color of the Sun and its planets, assuming all light levels to be in the normal color vision range of the eye [added: as would be seen from space]. The mosaic must have already been published or posted somewhere.

[Since Pluto is no longer a planet, we can ignore the lack of knowledge of its color and any mosaic that includes it will still be valid.]

Orange and yellow suns are invalid.

[KaiYeves]

Why is a yellow sun invalid?

[George]

A yellow Sun is an atmospheric colorful effect only. You won't see unfiltered Solar projections revealing a yellow Sun, unless the Sun is near the horizon. I hold to a white Sun, but I am hardly alone. If any of these folks have done a mosaic of the Solar system, then the colors might be right.

I strongly suspect, however, that no such near "true color" presentation of the Sun and planets has ever been done. I've got one hanging on my wall. It has no Sun, Venus is orange (from a false color surface image!), and Mars is brown. The more distant planets seem to be very accurate.

I do hope this draws some colorful attention to a colorful problem.

[ngc3314]

A yellow Sun is an atmospheric colorful effect only. You won't see unfiltered Solar projections revealing a yellow Sun, unless the Sun is near the horizon. I hold to a white Sun, but I am hardly alone. If any of these folks have done a mosaic of the Solar system, then the colors might be right.

I strongly suspect, however, that no such near "true color" presentation of the Sun and planets has ever been done. I've got one hanging on my wall. It has no Sun, Venus is orange (from a false color surface image!), and Mars is brown. The more distant planets seem to be very accurate.

I do hope this draws some colorful attention to a colorful problem.

You're making venerachromological comments now! Or maybe that should be cytherochromological. I had the impression that the orange hue was an average of more-or-less true color versions of the Venera surface images, driven almost completely by what spectral slices of sunlight manage to survive the many ricochets through the cloud decks. That would be a defensible surface color, albeit based on limited data and not actually representative of the surface rock if you depict the planet stripped of clouds.

[winensky]

A yellow Sun is an atmospheric colorful effect only. You won't see unfiltered Solar projections revealing a yellow Sun, unless the Sun is near the horizon. I hold to a white Sun, but I am hardly alone. If any of these folks have done a mosaic of the Solar system, then the colors might be right.

I strongly suspect, however, that no such near "true color" presentation of the Sun and planets has ever been done. I've got one hanging on my wall. It has no Sun, Venus is orange (from a false color surface image!), and Mars is brown. The more distant planets seem to be very accurate.

I do hope this draws some colorful attention to a colorful problem.

Ah the Easter Bunny has delivered a can of worms. "true colour". As the vast majority of amature astronomers have little choice but to acccept the limits of at least some atmospheric effects, it appears that you have eliminated their ground base observations from consideration.

Kind regards
Matt

[George]

You're making venerachromological comments now! Or maybe that should be cytherochromological. I had the impression that the orange hue was an average of more-or-less true color versions of the Venera surface images, driven almost completely by what spectral slices of sunlight manage to survive the many ricochets through the cloud decks. That would be a defensible surface color, albeit based on limited data and not actually representative of the surface rock if you depict the planet stripped of clouds.

I thought the surface was all radar mapping. You may be correct, but, since they never used the word "venerachromological" they may not have been as serious as one might expect.

What I want is a simple, typical color image of Venus as seen from space, which is the color of its atmosphere. It should be yellow with features. Here are some images of Venus taken from Magellan (a little brownish) and from Galileo. Perhaps being copyrighted reduces their popularity with publishers. Is that likely?

I don't know what cytherochromological means. It is not in my heliochromology textbook.

I'm still working on a call-to-arms for the Sun's color. What do you think of this one, "Heliochromology Rampant!"? It has a sort of "Big Bang" sound to it, right? [I still will restrict its use to ice cream socials, maybe. ]

As the vast majority of amature astronomers have little choice but to acccept the limits of at least some atmospheric effects, it appears that you have eliminated their ground base observations from consideration.

Indeed not, I too am an amateur. The Sun's color is not yellow because of the evidence from ground-based observations. If unfiltered Solar projections, seen terrestrially, are white, including the limb region, thus, how can adding back the scattered blues produce a yellow Sun? Blue and white can not make yellow. [This assumes that the blue color seen in the sky is representative of the net color that is scattered away from sunlight.]

As for the planets seen terrestrially, color correction shouldn't be too difficult since the amount of scattering by our atmosphere is known for various air masses or altitudes of the target.

[DyerWolf]

So, what are you looking for exactly?

Does someone have to find data that gives the emission / reflection spectra lines from spacecraft-derived-only sources and then color-correct space-craft-derived photographs into a mosaic you can see on your screen?

From what I've read, doing this would be further complicated by the fact that different computer monitors often display the same colors differently.

[George]

So, what are you looking for exactly?

A close approximation is fine.

I think the color images we have enjoyed of Saturn from Cassini are very close to "true" color. Similarly, the common images of Jupiter, Uranus, Neptune, and many Mars images are more than likely quite accurate, too. There aren't many natural color images of Venus, but I've seen one Galileo image for Venus that is probably close enough. There are images of Mercury that are probably correct, enough so that most of us here would likely agree upon it. Earth is certainly not a problem.

The Sun presents a little more of a problem, as most do not have a clear onderstanding as to its natural color. Some modern textbooks, however, do state the Sun as being a white star (e.g. Jeff Hester, et. al.). From space, it appears blinding white, which is not an indication of its natural color as seen at a properly attenuated level for our vision, yet since it appears mainly white overhead, and obviously white in space, why not white in a mosaic, even if the publisher doesn't really know just how likely white it really might be?

I've done one, but I am not the best person, especially on my list, that should be offering it. My hope is that someone has gone to the trouble to offer such a mosaic. If none exists, maybe it would be nice to add that to the IYA presentations for next year since it was officially 400 years ago that the colorful surface of any planet, excluding Earth, had ever been observed.

Does someone have to find data that gives the emission / reflection spectra lines from spacecraft-derived-only sources and then color-correct space-craft-derived photographs into a mosaic you can see on your screen?

Earth-based observations seem pretty close to the color as seen in space imaging, but they can be tweaked by bumping the colors in proportion to the known losses due to atmospheric scattering.

However, since all of the planets have been imaged with cameras revealing natural color, supposedly, why have I not seen one by now? Since many here have better access than I, then maybe several exist. I'll be glad to pay-up, and its not even a bet.

From what I've read, doing this would be further complicated by the fact that different computer monitors often display the same colors differently.

I would expect the vast majority come pretty close.

I'm not needing perfection, but something close.

Most posters are pretty close, but usually get Venus and the Sun wrong.

Notice that this poster comes close with all of them, but Venus. The Sun is pretty close. [I'm not crazy about he rings around Uranus, but that is beside the point.]

[WalrusLike]

A close approximation is fine....

George please correct me if I am wrong... but is the kind of thing that you are after, in a way, the answer to the question... 'Is that what it would look like through the porthole if I was approaching it?'

The sun is a special case since its a bit brightish.... but for the others... is that what you are after? (It is what I would like to see.... to show the kids....)

Nice idea... I hope someone with the time and capability to verify the science finds one....

[George]

George please correct me if I am wrong... but is the kind of thing that you are after, in a way, the answer to the question... 'Is that what it would look like through the porthole if I was approaching it?'

Yes. I should have qualified "natural" colors in the OP, so let me be clear...

If you were to travel to each planet, how would each appear to you as far as their natural coloration? Since the Sun's surface brightness is too bright, along with possibly Mercury and Venus, then we must use a true neutral filter, or other device (e.g. strobe, pinhole projecton), that would allow us to see the object within the normal photopic (color) vision range. [Objects too bright will always appear white if the colors of the spectrum are included. Once our color cones are maxed-out, white is the result, though at a normal intensity it could easily be any color, including yellow.]

[George]

Here is a pictoral guide through our Solar system that is probably close to true color. All of these come from APOD.

Mercury from Mariner 10… http://antwrp.gsfc.nasa.gov/apod/ap030216.html
Venus from Galileo.. http://antwrp.gsfc.nasa.gov/apod/ap040516.html
Earth from Apollo 17… http://antwrp.gsfc.nasa.gov/apod/ap990131.html
Mars per Hubble… http://antwrp.gsfc.nasa.gov/apod/ap990705.html
Jupiter… http://antwrp.gsfc.nasa.gov/apod/ap001226.html
Moons of Jupiter mosaic… http://antwrp.gsfc.nasa.gov/apod/ap970929.html
Uranus per Voyager II… http://antwrp.gsfc.nasa.gov/apod/ap010826.html
Neptune per Voyager II… http://antwrp.gsfc.nasa.gov/apod/ap980221.html

Sun (a bit too yellowish, though)… http://antwrp.gsfc.nasa.gov/apod/ap000925.html
Sun, beautiful colors it is not… http://antwrp.gsfc.nasa.gov/apod/ap051201.html

Here is another example on how to determine star color, including our Sun:
Orion focused… http://antwrp.gsfc.nasa.gov/apod/ap030207.html
Orion defocused… http://antwrp.gsfc.nasa.gov/apod/ap980829.html

The defocus approach accentuates the more natural color of the star. The solar twins I've found seem to be all white when defocused, further evidence for a non-yellow star to place in a near, true color mosaic.

[Hornblower]

Here is a pictoral guide through our Solar system that is probably close to true color. All of these come from APOD.

Mercury from Mariner 10… http://antwrp.gsfc.nasa.gov/apod/ap030216.html

Mariner 10 did not take any color photos, according to an article by Andrew T. Young of San Diego State University, published in Sky and Telescope, May, 1985. In that article he provided swatches of color for most of the planets, along with the Moon, Io and Titan. The swatches were generated from reflectance spectra that were not subject to the limitations of many of the spacecraft.

I will go into it more in a later post, and I will try to scan and upload the swatches.

The swatch for Mercury was much browner than the neutral gray on the black-and-white image shown in the linked page. Let me add that those pages make no claims about the accuracy of color rendition.

[George]

Mariner 10 did not take any color photos, according to an article by Andrew T. Young of San Diego State University, published in Sky and Telescope, May, 1985.

In that article he provided swatches of color for most of the planets, along with the Moon, Io and Titan. The swatches were generated from reflectance spectra that were not subject to the limitations of many of the spacecraft.

I will go into it more in a later post, and I will try to scan and upload the swatches.

The swatch for Mercury was much browner than the neutral gray on the black-and-white image shown in the linked page. Let me add that those pages make no claims about the accuracy of color rendition.

Thanks. I should have qualified them. It took a while to make the link list as I went through every APOD image. Ug. By the time I found all that I could, I had forgoten I had even claimed they were near to true color, though that had been my objective.

The APOD link I gave for Mercury, however, is not a typical false color image, at least in any dramatic way. [I know what little color is there is important for scientific study, so l do want to remind others that true color is not much of a great scientific goal. Getting close to true, or natural, color is more valuable for PR and art, than science.] The image may still prove to be pretty close to true color since it is so gray, typical of what we should expect. Is this likely?

In the last hour, I stumbled into the latest from Messenger. I found it on Astronomy's next cover issue, as is shown on their website. Here is one image that may or may not be indicative of what one might see in natural color. It is tempting to think it might be close.

Messenger's MDIS package (one narrow and one wide angle camera) uses 11 filters, which, as they put it, allows them to see "much like our eyes do", though no specific image mentions such a case. It would surprise me to see a near true color image actually reveal much color at all.

[Hekate's Lair]

Shouldn't this be the natural colour of the Sun? It's on fire, after all.

http://umbra.nascom.nasa.gov/eit/ima..._and_earth.jpg

[George]

Tis beautiful.

Since a 2,000K tungsten filament produces a yellow-white glow, what color should a 50,000K to 100,000K CME cloud look like? It won't be orange-red.

[DyerWolf]

Thanks George.

This has turned into a very interesting discussion - and I really enjoyed the links you provide. Best luck with your search.

[George]

Thanks. This is one of those areas amateurs like me can jump in and help out. It is a fun quest, too.

[Hornblower]

Here are the swatches from Andrew T. Young's article in Sky and Telescope. Each one is averaged over the face of the respective object. They are in the following pattern:

Mercury Moon Mars

Jupiter Io Titan

Uranus

White background

[img=http://img187.imageshack.us/img187/9541/planetcolorscg7.th.jpg]

Black background

[img=http://img187.imageshack.us/img187/3355/planetcolorsdarkbackgroyg7.th.jpg]

I had trouble getting a decent photocopy, either with the scanner or with my digital camera, so I eyeballed them, looking at the magazine under a light that made the paper look really white, and matching the swatches in my PaintShopPro software.

Mr. Young used the best available reflectance spectral measurements, including the Viking landers for Mars. He transformed the spectra into CIE coordinates to get the additive primaries, which he then converted to Munsell coordinates for pigments. With the assistance of some paint experts he was able to create the swatches, which Sky and Telescope reproduced as closely as possible with the halftone printing process.

Mr. Young reminded us that the Voyager cameras, for all of their marvelous imaging capability, were not reliable sources for the giant planets, because of their limitations in working the red end of the spectrum. Thus he used Earth-based observations. He omitted Saturn because of difficulty in distinguishing between the cloud tops and the rings with the available equipment, but added that it generally is similar to Jupiter in hue. He also omitted Venus, which he described as "brilliant white".

[George]

Here are the swatches from Andrew T. Young's article in Sky and Telescope. Each one is averaged over the face of the respective object. They are in the following pattern:

Mercury Moon Mars

Jupiter Io Titan

Uranus

The Moon and Mars seem much too brown to me. Were any Moon rocks that brown? JPL put considerable effort into color calibration for the rovers, but I have the impression that Mars is more red, similar to Hubble's images, maybe.

Part of the color problem can be found in taking an average color. Jupiter has a wide range of colors, though his average seems reasonable. His Io seems too pale, though he may be close as an average. I don't know. For Titan, it seems contrary to Cassini's images, which I thought were close to natural colors.

Mr. Young used the best available reflectance spectral measurements, including the Viking landers for Mars. He transformed the spectra into CIE coordinates to get the additive primaries, which he then converted to Munsell coordinates for pigments. With the assistance of some paint experts he was able to create the swatches, which Sky and Telescope reproduced as closely as possible with the halftone printing process.

That is a lot of work, no doubt. I can only think of two other ways to better that effort: color calibrated telescope imaging systems, and the asterochromometer (if completed).

[The asterochromometer is a little instrument that simply takes a known light source and produces a spectrum that becomes masked at the wavelengths necessary to recreate the original spectral irradiance of the target. [Since y'all can get the hard sp. irr. data, then why not use it.] The adjusted spectrum is then recombined to create a homogenized color spot for any observer to simply see. To verify that the mask did the trick, a spectrometer simply produces the sp. irr. of the spot for comparison. Any error for any given wavelength can be corrected by adjusting the mask to allow more or less light through the mask for that wavelength. This also gives only the average color of the object, however. Also, I built it in an effort to discover the Sun's color. The recombination module was a lens system and is weak in recombining the blues and violets, so a scrambled fiber optic system has been designed. However, considering the amount of effort it will take to complete it, it has now fallen into the category of... "it's too much squeeze for the juice". It would be far easier for NASA to add a quick look at the Sun with a strobe or super neutral filter and simply tell us what it looks like, or photograph it, too.]

My own ignorance, perhaps, of the CIE process may be at fault, but it doesn't seem to be the best approach. Maybe it is the knowledge and experience level of the artist that is the key. Here is one site that uses this process and has determined the Sun is peachy-pink. I'd bet another Sundae that it is not peachy-pink. It ain't a girl star!

I think I can easily find some natural color images from Hubble and Cassini to compare to this work, but do you want me to? The mosaic goal is to represent more than just a flat average color, but to represent the planet as we might actually see it. This means Jupiter should have the color bands, etc.

Mr. Young reminded us that the Voyager cameras, for all of their marvelous imaging capability, were not reliable sources for the giant planets, because of their limitations in working the red end of the spectrum.

That's good to know. His Uranus is much more greenish than Voyager's images. I'm not sure why that would be the case if red is the problem. I assume too much red would be the Voyager issue which would have not produced such a blue image as seen in the APOD link for Uranus. But, the processing might have overcompensated for the red issue and made it too blue. Just guessing, of course.

He also omitted Venus, which he described as "brilliant white".

That may be due to overexposure since it does have a very high surface brightness due to its proximity to the Sun.

Thanks, Hornblower, for your efforts. This is certainly interesting to see.

[WalrusLike]

Um.. I think that a average colour patch... (and I do appreciate it is useful and that a lot of work goes into it)... does not really indicate 'What would it look like as I approach?'

You wouldn't think this was so hard till you remember that there are no tourists swanning around with instamatic polaroids to catch a quick shot of Jupiter on the way by... Rather the images we get come from high tech instruments designed to gather data that is not necessarily aligned with the goal of a 'happy snap'.

This is fun... I have enjoyed reading everyone's input... thanks George and contributors.

[George]

You wouldn't think this was so hard till you remember that there are no tourists swanning around with instamatic polaroids to catch a quick shot of Jupiter on the way by... .

All the more reason we need to establish proper color identity soon so that the inevitable tourists don't make things worse.

[eburacum45]

Mars probably is quite brown, and so is the Moon, in their own distinctive ways. Mars' colour seems to come from a thin layer of dust, which includes haematite; a browny-red rather than red mineral.
Take a look at this post from Fridger Schrempp over at Celestia
http://www.shatters.net/forum/viewto...267&highlight=

The Moon seems to be quite brown too, if this Galileo image is anything to go by (not guaranteed)
http://nssdc.gsfc.nasa.gov/planetary...rthmo2_big.gif

[Disinfo Agent]

For Venus, I think there was a more recent picture. This one?
Oh, and the Messenger pictures, though I'm not sure they included colour versions.

[George]

Mars probably is quite brown, and so is the Moon, in their own distinctive ways. Mars' colour seems to come from a thin layer of dust, which includes haematite; a browny-red rather than red mineral.
Take a look at this post from Fridger Schrempp over at Celestia
http://www.shatters.net/forum/viewto...267&highlight=

That was in 2003, which preceeded the rovers. I would bet the rovers are the most accurate due to the extensive color calibration effort prior to the mission, as well as, the color pedestal with sky mirror.

But, it does seem that his color estimate was pretty close. Mars is a little more brown than what the Hubble processed images have rendered.

Here are some "approx. true color" Spirit images:
http://marsrovers.jpl.nasa.gov/galle...20060609a.html
http://marsrovers.jpl.nasa.gov/galle...20040401a.html
http://marsrovers.jpl.nasa.gov/newsr...20051205a.html
http://marsrovers.jpl.nasa.gov/galle...20040121a.html

Here are some Opportunity images:
http://marsrovers.jpl.nasa.gov/galle...20040506a.html
http://marsrovers.jpl.nasa.gov/galle...20040128a.html
http://marsrovers.jpl.nasa.gov/galle...20050228a.html
http://marsrovers.jpl.nasa.gov/galle...20050728a.html
http://marsrovers.jpl.nasa.gov/galle...-B019R1_br.jpg

For some reason, Spirit presents a browner Mars than does Opportunity. I'd like to think it is a surface regional issue, not a rendering one.

The Moon seems to be quite brown too, if this Galileo image is anything to go by (not guaranteed)
http://nssdc.gsfc.nasa.gov/planetary/lunar/gal_earthmo2_big.gif

I hope you're kidding.

[George]

For Venus, I think there was a more recent picture. This one?

That is an intersting one. It is less yellow than the two I've found. I am surprised at how few images are available that attempt to show the planet's natural color.

[eburacum45]

I hope you're kidding.

That image is apparently 'colour enhanced'
according to this linking page
http://www2.jpl.nasa.gov/galileo/earthmo2.html
so is not much use for our purposes.

[AndreasJ]

I don't know what cytherochromological means. It is not in my heliochromology textbook.

It should mean something like "concerning the study of the colour of Venus".

"Cytherean", derived from an ancient epithet of the goddess, is an adjective refering to Venus thought up by people who thought "Venerean" was too close to "venereal" and "Venusian" too barbaric.

[George]

That image is apparently 'colour enhanced'
according to this linking page
http://www2.jpl.nasa.gov/galileo/earthmo2.html
so is not much use for our purposes.

Ah, that makes more sense.

A full Moon is only about 2,500 cd/m², IIRC. This surface brightness is in the comfortable range of our photopic (color) vision. Thus, if it appears white to us here, it will look white up there. Of course, it can also be gray, which will look white if the background is dark.

No doubt there are subtle color variations in small regions. I remember the excitement of one Apollo lunar explorer when he ran across a very orange region along a crater rim. But this was a very small and unusual circumstance.

[George]

It should mean something like "concerning the study of the colour of Venus".

"Cytherean", derived from an ancient epithet of the goddess, is an adjective refering to Venus thought up by people who thought "Venerean" was too close to "venereal" and "Venusian" too barbaric.

In my response to him, I feared my prior post might stir a negative response and I actually read it as a veneral.

Now that Star Wars dominates, Cytherean may not work as well.

It is nice to learn some big words, and I'm not as hippopotomonstrosesquippedaliophobic as I used to be.

[eburacum45]

Ah, that makes more sense.

A full Moon is only about 2,500 cd/m², IIRC. This surface brightness is in the comfortable range of our photopic (color) vision. Thus, if it appears white to us here, it will look white up there. Of course, it can also be gray, which will look white if the background is dark.

No doubt there are subtle color variations in small regions. I remember the excitement of one Apollo lunar explorer when he ran across a very orange region along a crater rim. But this was a very small and unusual circumstance.

The Moon's albedo is similar to the albedo of a grey tarmac road. If a square meter of lunar surface were brought to Earth it would look darker than most surfaces we normally encounter. I spent the hot, sunny summer of 1976 measuring the albedos of a range of surfaces in the English countryside; fields, concrete, soil. It was all a very long time ago but I seem to remember that they were all brighter than the average lunar albedo.

The dark grey surface of the Moon might have a tinge of brown in it; this page by Filipe Alves has some interesting enhanced and saturated images, but also some which purport to show the true colour.
http://www.atalaia.org/filipe/moon/colorofthemoon.htm