Blue skies, blue seas: sky and ocean colours?

[Evil Dr Ganymede]

I was wondering about whether oceans of different liquids would look blue or not. I know that our own water oceans were blue in part because they absorb longer (red) wavelengths of light and let the shorter (blue) ones through a larger distance. But I had a look around for more info on the web, and it seems that the sea is blue because of that absorption and also because it reflects the sky, and the sky is blue because of rayleigh scattering:

http://www.madsci.org/posts/archives/fe ... .Bc.r.html
http://www.madsci.org/posts/archives/de ... .Es.r.html
http://www.madsci.org/posts/archives/de ... .Ph.r.html


So, reading those, would I be right in assuming that the atmospheric composition is actually irrelevant to the colour of the sky? i.e. it doesn't matter what gases the atmosphere is made of - so long as there are no particulates, aerosols, hazes, dust particles etc - then the sky will always be blue? (if there are aerosols etc, then the sky can be different colours).

That being the case, liquid on the surface would reflect the sky colour, but what about the contribution of absorption in the liquid? Would liquid ammonia or liquid methane also let the blue light through furthest while absorbing the red? Or would they have different characteristics?

[ArneB]

http://saturn.jpl.nasa.gov/multimedia/i ... -br500.jpg

At least that's the case with Saturn

[PlutonianEmpire]

I was wondering about whether oceans of different liquids would look blue or not. I know that our own water oceans were blue in part because they absorb longer (red) wavelengths of light and let the shorter (blue) ones through a larger distance. But I had a look around for more info on the web, and it seems that the sea is blue because of that absorption and also because it reflects the sky, and the sky is blue because of rayleigh scattering:

http://www.madsci.org/posts/archives/fe ... .Bc.r.html
http://www.madsci.org/posts/archives/de ... .Es.r.html
http://www.madsci.org/posts/archives/de ... .Ph.r.html


So, reading those, would I be right in assuming that the atmospheric composition is actually irrelevant to the colour of the sky? i.e. it doesn't matter what gases the atmosphere is made of - so long as there are no particulates, aerosols, hazes, dust particles etc - then the sky will always be blue? (if there are aerosols etc, then the sky can be different colours).

That being the case, liquid on the surface would reflect the sky colour, but what about the contribution of absorption in the liquid? Would liquid ammonia or liquid methane also let the blue light through furthest while absorbing the red? Or would they have different characteristics?

Ya know, i've always wondered about that too...

[Terminator]

...However, if you actually go out on the ocean, it appears much more gray than blue. That's why they paint warships gray and not blue.

[tony873004]

. I remember hearing that water actually does have a blue tint, but I still think it's more sky reflection than anything. I have a view of the ocean from my bedroom. On cloudy days, it looks gray, on sunny days, it looks blue, and at night it looks black.

[Evil Dr Ganymede]

OK, so a lot of it seems to be down to reflection of the sky... but does anyone actually know what wavelengths non-H2O liquids absorb?

[ajtribick]

I'm not sure if when viewed from space the blue sky explanation applies, since the reflection of water varies with angle. Certainly it applies near ground level when the viewing direction is nearly parallel with the water surface, but I'm not sure about high angles - the amount of reflection falls off at high angles.

[Rassilon]

I am almost willing to bet that the water scatters light much in the same way air does, noteing the similartities in color....

As for other liquid types I suppose it would have a slight tint of its natural color but mostly reflect the light the same way the sky does depending on its albedo...or the sky color reflected off its surface....A good example is chrome...Its obviously of a different composition and its color greatly depends on what it reflects....

Usually I do alien planets where the sky color is the same as the water color...Tends to look more natural...

Now lets say the water of some planet is lava...Of course it will reflect its natural color...orange....

Methane seas...I think methane is naturally a deep blue...so methane under a red sky could be purple?

Water with a high copper content or algae may be greener than normal and reflect less due to the amount of solids floating on the surface?

Murky water...Would this resort to being the color of the terrain...mud or sand?...This sort of water tends to be less reflective of the sky color...

All in all I believe water has no color much like plain glass...I believe the color itself is as I stated above due to scattering in volumes...

[kikinho]

I'm starting creating my system. Maverick is a planet with an yellow/orange atmosphere due to the high concentration of sulphur and other sulphur-based gases. Has three oceans of hidrosulfuric acid (H2SO4). The oceans are dark because they are between 7 and 10 km deep, and the color of them are the same as the atmosphere: yellow/orange.

Another planet is Alkemira. The atmosphere is made of nitrogen, nitrogen, ammonia, some nitrogen dioxide and some methane. This results in a brown atmosphere. The oceans are made of ammonia, and reflects the color of sky, resulting in a brown/grey color.

Also the star color is orange, a K7V star. I think that redder colors may influence in atmospheres/oceans colors.

One thing I want to know. There's also a planet called Muphridna and is similar to Earth, but the lowest part of the atmosphere is green due to the high concentration of algae. If this planet or Earth were being illuminated by an orange star, would the color still be blue or have another color?

[eburacum45]

Orange stars aren't very orange; if you were on an Earth-like planet around such a star you probably would hardly notice the difference. The sun would be a little bigger in the sky, as the planet would be closer to it.

Why not have the lower sky greenish due to the algae, fading to a blueish upper sky?

[Matt McIrvin]

So, reading those, would I be right in assuming that the atmospheric composition is actually irrelevant to the colour of the sky? i.e. it doesn't matter what gases the atmosphere is made of - so long as there are no particulates, aerosols, hazes, dust particles etc - then the sky will always be blue? (if there are aerosols etc, then the sky can be different colours).

That's going to be true as long as Rayleigh scattering is the dominant process involved; there's nothing about it that is greatly dependent on composition. But the color might come out differently even in the absence of aerosols or particulates if some resonant absorption or scattering is important for visible light. I suppose this would correspond to cases in which we would see the gas itself as noticeably colored.

Also, in practice it seems that for solid bodies in our solar system, clear atmospheres whose appearance is not dominated by aerosols or particulates are more the exception than the rule.

[kikinho]

But the planet i'm creating have a green and a dark blue atmosphere, due to the less brightness compared to the Sun. Before the star was K7V, but now is K5V, but it's continue to be many more times darker than the Sun. It have a radius of 0.93 Rsun. The star is older than Sun.

[kikinho]

But the planet i'm creating have a green and a dark blue atmosphere, due to the less brightness compared to the Sun. Before the star was K7V, but now is K5V, but it's continue to be many more times darker than the Sun. It have a radius of 0.93 Rsun. The star is older than Sun.