So what colour is Uranus really? Options

[karolp]

Photos from the Voyager era show it to be on the border of blue and green, particularly greenish in some of them. On the other hand, amateur astronomers report from their backyards a definite "blue blob". So what colour would Uranus appear to human eye? Was the greenish tint made up as a distinction from Neptune? Or was it some flaw in image processing?

[djellison]

I've seen it through a 16" scope, and it was a small bluey-green ball - looking at the amateur obs of it, this isn't too far from how I remember it

http://i105.photobucket.com/albums/m213/me...ectspelling.png

But there is a whole variety from bright bright blue to near a turq-green in the images I've seen.

Doug

[karolp]

Check this out (the occultation was visible in Australia):

Uranus occultation

And yes, I have also seen a great variety, especially in printed books and magazines. But what is its true colour? With the DPS taking place recently there must have been some mention of that as well... Especially that the colour is probably changing a bit due to the rapid increase in atmospheric activity with Uranus near its solstice where both hemispheres get sunlight and things get stirred up a bit...

[MizarKey]

karolp, thanks for sharing those occultation images, I've always been a big fan of the moon passing in front of the outer planets and brighter stars.

[Rob Pinnegar]

Those occultation pictures are neat but I'm sure they've been altered a little. Look at how bright Uranus appears to be, compared with the limb of the Moon! Although Uranus is probably several times more reflective than the Moon, it also gets 400 times less sunlight. I expect its brightness has been increased to make it more visible.

A lot of kids' astronomy books portray Uranus as green and Neptune as blue, but (as has been pointed out above) this is probably just "artistic license" to help children distinguish them from each other. Uranus is blue, but it's not as blue as Neptune -- it has that touch of green to it which Neptune pretty much completely lacks. More of a cyan-blue.

[JRehling]

A lot of kids' astronomy books portray Uranus as green and Neptune as blue, but (as has been pointed out above) this is probably just "artistic license" to help children distinguish them from each other. Uranus is blue, but it's not as blue as Neptune -- it has that touch of green to it which Neptune pretty much completely lacks. More of a cyan-blue.

I agree. I've seen Uranus and Neptune in very tight succession (within 5 minutes) of each other, and the difference (besides the very large difference in brightness) was obvious: Uranus is greener... but still blue-green, not out-and-out green.

I've also seen Uranus and Mars in rapid succession, which is an astonishing difference in color -- in some respects, the largest difference in color you can see in the sky without developing a long exposure of something or other.

[Guest_Kevin Heider_*]

Uranus July 8, 2005 with a Meade 12 inch 200LX-GPS f/10.

-- Kevin Heider

[4th rock from th...]

Well, to me visually it looks the same color as the light blue on these pages, for example on the second row background, were you have "Front Page" "Forum Guidelines", etc.
This on a 8'' telescope, so not much light to detect subtle colors, but certainly not much saturated light blue.

Neptune is close to the background on the page footer, where you have the time.

This to me of course, but we are talking about visual appearance.

[algorimancer]

It's been 15-20 years since I last had a look at Uranus, but I recall it as a small but sharp and brilliant emerald green disc through the 6" reflector I had at the time. These days I have an 8" Celestron, but unable to get much use out of it due to the laser correction I had on my eyes a few years ago... wonderful vision in bright daylight, but bad flares and ghosting in the dark. Anyway I'm having plenty of fun with the math and software end of things these days.

Some of this perceived color variation may be due to the optical glass in the scopes and eyepieces. Part of it may be individual variation. I'm pretty sure that the true color is green, and blue for Neptune. Saturn of course has that nice golden hue, but I don't recall that Jupiter had any special color beyond levels of gray; the red spot never looked red to me.

...Uranus July 8, 2005...

That last one was really nice, Kevin. Someday I need to try that image stacking thing.

[odave]

I've always seen it as greenish through my battery of 'scopes (80mm/8"/12.5"), especially when compared to Neptune in the same session, as JRehling notes. Now is a good time to try that, with both of them hanging out relatively close to each other in Aquarius & Capricornus in the early evening.

Jupiter's red spot has been very pale for the last several years, and they way I've detected it most often is by the gap it makes in the SEB. Find the gap first, then concentrate on it and the spot becomes a little more apparent. It certainly doesn't hit you over the head these days.

But as others have noted, we are using our own built-in biological photodetectors in the end, and they have their quirks. This discussion reminds me of the whole green star question, but we're dealing with emitted light there. Interesting stuff!

[ugordan]

This discussion reminds me of the whole green star question

By chance there are no stars nearby that would have produced green colors had their spectral shapee been just right.

Isn't the whole point that a blackbody cannot have an apparent green color (it cannot have a spectral shape "just right") because of the blackbody curve and the way color is perceived by humans? This statement above makes it look like there can be green stars in reality and that it just so happens none of them are near enough...

[odave]

Yup, I remember quite a debate on this topic back in my Usenet days. This article has a better explanation.

[J.J.]

In almost all of the amateur images I've seen of both planets (such as those on the ALPO site), Uranus is definitely more greenish than Neptune, the latter of which is usually an out-and-out blue.

[Airbag]

Slightly off topic...I was inspired by HST's near IR image of Uranus to create this shallow glazed ceramic bowl.

Airbag

[Floyd]

That is really great. Have you created bowls for other planets? Mars?

Floyd

[Airbag]

Thanks! No, I do not have the right glazes for Mars (yet?) but Neptune is next.

Airbag

[JRehling]

Thanks! No, I do not have the right glazes for Mars (yet?) but Neptune is next.

Airbag

I have a whole set of Venus plates -- came straight from the store!


Kudos on the Uranus plate. Now you have to tell guests "I'm eating..." ... nevermind.

[elakdawalla]

I'm resurrecting this old thread because while the conversation was interesting and produced some great links (I especially like that occultation set of images linked to in post 2 by karolp), the thread never resolved in my mind. I would LOVE to see someone post a side-by-side comparison of Voyager 2 Uranus and Neptune images that show their relative color. It's not hard to get the Voyager 2 data but the production of approximately correct color is still a black art to me. Anybody feel like attempting it? I am also looking for a nice amateur-processed image of Uranus for the Advent Calendar I'm doing in the blog...come on, can anybody do better than the Voyager team did back in 1986?

[ugordan]

Have you tried Views of the Solar System site?

[elakdawalla]

No because I hate that website's over-the-top obnoxious ads so much...

[Antdoghalo]

Have you tried Views of the Solar System site?

It doesnt have any images from Hayabusa(Which is only mentened breifly in space exploration chronology)
Nor does it have the Steins flyby images Or any images from New Horizons of Ios Tvashtar Patera erupting.

But it does have some great maps and images including some good Voyager 2 and Hubble images of Uranus showing some clouds on it.

[tedstryk]

No because I hate that website's over-the-top obnoxious ads so much...

It is kind of sad. Calvin Hamilton made pleas for years for users to contribute to the webhosting cost (which at the time were much greater for a site like that than now). Almost no one came forth, and in came the ads.

This is one of the best examples....http://hubblesite.org/gallery/album/solar_system/pr2007032c/

Both worlds are blue-green. The blue appearance of many images is thanks to Voyager color shifting.

[Ron Hobbs]

I have always thought that this was the definitive view of the color of Uranus. To my eye it seems steel gray. Maybe some of those here with artistic eyes can comment on this version.

I too despise the ads of the Views of the Solar System site, though I clicked on it and waded through the ads. The image at this site has a decided greenish caste to my eye. I remember hearing that Uranus is less blue than Neptune because the clouds on Uranus are higher than on Neptune and so there is less of a depth of clear methane gas to absorb the red light. I wonder if there is a seasonal effect at work on Uranus.

[stevesliva]

Adblock Plus seems to be catching them all. I don't see a single one.

[JohnVV]

No because I hate that website's over-the-top obnoxious ads so much...

adds what adds
i use No-script and ad block pulse
along with some sites in my HOST file redirected back to 127.0.0.1 ( about 12,000 of them)

i guess i am a bit spoiled by not seeing 95%+ of the adds
i have always gone with these colors ( except for the now missing "great dark spot")
[attachment=19973:neptune.jpg] [attachment=19974:uranus.jpg]

[tedstryk]

Using Voyager color is treacherous. I strongly recommend Hubble or Voyager OGV images shifted to match Hubble color.

[JGodbaz]

Since the Voyager camera had very little true red response, it's a bit difficult to do anything. Essentially it comes down to inverting a highly singular matrix to recover the spectral curve for each pixel; a pretty standard inversion problem, but no simple regularisation techniques will get you what you want because it's so underdetermined.

I suppose you could probably use low res multispectral images to create a statistical model of how red correlates with the various other colours Voyager actually recorded and try to recreate the missing colours. I'm a bit too busy at the moment to give it a go, but if suitable reference data is available then it ought to be possible at least. Might be worth a paper if someone actually does it!

[4th rock from th...]

If you want to have fun, here are two links to Uranus and Neptune spectra:

http://lasp.colorado.edu/~bagenal/1010/gra..._outplanets.gif

http://solarasph.wikidot.com/the-visual-spectrum-of-uranus

It's possible to derive a global color from the spectral data and use it as a guide to fine tune the images. My understanding (and visual experience at the telescope) is that the colors normally displayed on the released images are OK, apart from a little of saturation.

I'd also say that the color scheme on the forum's skin is actually close to the planet's visual impression!
The title bar with the member's name and post time is Neptune like, and the post body background color is similar to Uranus color.

[machi]

This is my experiment with Uranus images.
But I don't think, that it's in real colors.
It's enhanced color composite (green, orange and blue filter).

Attached thumbnail(s)

 

[Decepticon]

^ So what would it look like in real colour?


Nice to see the faint cloud features.

[machi]

I tried to match color to approximately real look.
But saturation is higher than in real and reddish edges are artifacts from image processing (probably, I wasn't in vicinity of Uranus in my life ).

[JGodbaz]

The problem with having only one spectra is that you can get the mean colour of Uranus perfect, but that doesn't necessarily imply that you get the colour of any specific features correct.

I was thinking of something more along these lines (although this is probably too simple a model to work very well):

* Take a low res spectral cube of Uranus in the visible (say 15x15x15). assume that each spatial pixel is a sample from a multivariate Gaussian distribution. Determine the mean and covariance matrix from the data. Assume that the Voyager pictures of Uranus actually look vaguely like Uranus when you took the spectral cube (not likely I know).

* Each one of the Voyager images corresponds to sampling the inner product of the combined filter/imager spectral response with the actual spectra at that pixel. Thus a sequence of images can be considered a matrix transform for each pixel. The matrix transformation can then be written up as an optimisation problem trying to maximise the posterior probability of the spectra for a pixel versus the measured data using the known spectral relationships as a prior and a positivity constraint. This would require some sort of noise modelling (I have no idea what the noise characteristics of a Vidicon tube are). Unfortunately the positivity constraint means that it would probably require some sort of iterative solution.

* Given the estimated spectra for each pixel, conversion to RGB (or whatever format you want) is a pretty standard linear transformation.

Any thoughts? The premise is that missing colours like red (and indistinguishable colours) can be inferred from the presence of of other colours given prior knowledge of what Uranus looks like.

[Guest_PhilCo126_*]

Well through a refractor it looks white-blueisch

[siravan]

Regarding visual inspection of Uranus color through a telescope, one needs to remember that human eyes are not a perfect camera either and are in fact more sensitive to green wavelengths than blue (or, for that matter, red). Depending on how large a scope you are using and how bright Uranus looks, it may appear blue or green. To me, it looked "green", but I was looking through a puny 10x40 binocular.