# What would a methane sky look like? **URL:** \ **Category:** Factual Questions\ **Created:** [September 30, 2009, 10:51pm UTC](https://boards.straightdope.com/t/what-would-a-methane-sky-look-like/512171 "2009-09-30T22:51:20Z")\ **Posts on this page:** 5\ **Page:** 1
**Author:** ![tracer](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/tracer/32/20578_2.png) [@tracer](https://boards.straightdope.com/u/tracer)\ **Post date:** [September 30, 2009, 10:51pm UTC](https://boards.straightdope.com/t/what-would-a-methane-sky-look-like/512171/1 "2009-09-30T22:51:20Z")
The pictures of Titan’s surface taken by the Huygens probe show a hazy, yellow-orange sky above the horizon. Thing is, Titan’s atmosphere is over 98% nitrogen, and less than 2% methane. AND, that atmosphere is hella thick, with a pressure of over 120 kPa at the surface. What I’m wondering is: What would the sky look like on a nice, bright, sunny day on a planet with a THIN atmosphere composed PRIMARILY, if not almost ENTIRELY, of methane? Would the sky look orange, like on Titan? Or would it look blue, due to the scattering of sunlight, like Earth’s air does? ---
**Author:** ![Fear\_Itself](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/fear_itself/32/19637_2.png) [@Fear\_Itself](https://boards.straightdope.com/u/Fear_Itself)\ **Post date:** [October 1, 2009, 10:59am UTC](https://boards.straightdope.com/t/what-would-a-methane-sky-look-like/512171/2 "2009-10-01T10:59:57Z")
[The Sky on Alien Worlds](http://www.orionsarm.com/xcms.php?r=oa-page&page=gen_skyonalienworlds) > [@](#): > > In the visible range nearly all common and probable atmospheric gases are transparent. The exception is methane. Methane absorbs red light, and therefore to the human eye an atmosphere with even a few percent methane appears blue-green under standard sol type illumination. This accounts for the appearance of Uranus and Neptune in today’s solar system, and indicates that the sky of the early earth might have had a greenish tinge. Under sunlight methane forms a reddish smog-like haze, so if the proportion of methane is quite large (as on the moon Titan) the sky becomes hazy and reddish instead. This would probably not happen in an oxygen-nitrogen atmosphere breathable to humans, since methane would not likely exceed a few percent. In the presence of oxygen methane oxidizes into carbon dioxide and water. ---
**Author:** ![CalMeacham](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/calmeacham/32/35_2.png) [@CalMeacham](https://boards.straightdope.com/u/CalMeacham)\ **Post date:** [October 1, 2009, 12:07pm UTC](https://boards.straightdope.com/t/what-would-a-methane-sky-look-like/512171/3 "2009-10-01T12:07:59Z")
fascinating references – I’ll have to copy those and add them to my collection. But, if I read the linked page and articles correctly, an atmosphere of 120 kPa would be 1.2 bars, and would therefore fall between the Earth-type blue and the 10 bar cyan atmosphere, so would be between the middle two colors, and closer to the Earth one. With only 2% methane and relatively low pressure, why does the sky look so yellow? The linked page indicates over 10 bars needed (maybe as much as 40) for yellow. That’s 1 million to 4 million pascals, according to the nifty converter > **[Bars to Pascals Conversion Calculator](http://www.unitconversion.org/pressure/bars-to-pascals-conversion.html)** > > Bars to Pascals Converter ---
**Author:** ![tracer](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/tracer/32/20578_2.png) [@tracer](https://boards.straightdope.com/u/tracer)\ **Post date:** [October 1, 2009, 6:03pm UTC](https://boards.straightdope.com/t/what-would-a-methane-sky-look-like/512171/4 "2009-10-01T18:03:24Z")
> [@CalMeacham](#): > > But, if I read the linked page and articles correctly, an atmosphere of 120 kPa would be 1.2 bars, and would therefore fall between the Earth-type blue and the 10 bar cyan atmosphere, so would be between the middle two colors, and closer to the Earth one. With only 2% methane and relatively low pressure, why does the sky look so yellow? The linked page indicates over 10 bars needed (maybe as much as 40) for yellow. That’s 1 million to 4 million pascals, I suspect Titan’s atmosphere looks yellowish not because of the methane, but because of the “methane smog”. As **Feat Itself** ’s quote states: > [@](#): > > Under sunlight methane forms a reddish smog-like haze, so if the proportion of methane is quite large (as on the moon Titan) the sky becomes hazy and reddish instead. It would be interesting to know what kinds of materials this haze is made out of. Longer-chain hydrocarbons, maybe? ---
**Author:** ![tracer](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/tracer/32/20578_2.png) [@tracer](https://boards.straightdope.com/u/tracer)\ **Post date:** [October 1, 2009, 8:55pm UTC](https://boards.straightdope.com/t/what-would-a-methane-sky-look-like/512171/5 "2009-10-01T20:55:32Z")
> [@tracer](#): > > It would be interesting to know what kinds of materials [Titan’s] haze is made out of. Longer-chain hydrocarbons, maybe? Wikipedia to the rescue: > [@](#): > > … trace amounts of other gases such as hydrocarbons (including ethane, diacetylene, methylacetylene, acetylene, propane), cyanoacetylene, hydrogen cyanide, carbon dioxide, carbon monoxide, cyanogen, argon and helium. The orange color as seen from space must be produced by other more complex chemicals in small quantities, possibly tholins, tar-like organic precipitates.