# Would Rayleigh scattering (blue skies) be noticeable in an O'Neill cylinder?

In my story there is a full size (Island Three) O'Neill cylinder, 5 miles in diameter and 20 miles long.

It doesn't have windows, but is lit internally down the center of the cylinder with a 20 mile long, very bright, full spectrum lamp.

There is a budding artist in my story who lives there.

As imagined when she looks up the sides of the cylinder, she sees her neighbors from down the road overhead, would there be a bluish tint to their landscape which is in the distance, 3-5 miles away?

Also, if she stands at the very "north" end of the cylinder and has a clear view all the way to the "south" end, 20 miles away, would she see any blue or bluish sky due to Rayleigh scattering and the long linear "sun"?

• Aerial perspective is a thing. Mountains appear blueish in the distance, say 20 km or so. Commented Sep 28, 2018 at 21:48
• I'm pretty sure the answer's no, but I don't have time to work it all out. Here are some good articles, the second has software that might calculate it for you. It's complex because gravity, pressure, and composition are all involved. On Rayleigh Optical Depth Calculations by BARRY A. BODHAINE, NORMAN B. WOOD, ELLSWORTH G. DUTTON, JAMES R. SLUSSER and Simulated Rayleigh Scattering by James Nelson
– JBH
Commented Sep 29, 2018 at 0:53
• "And purple mountains, majesty/Above the fruited plains"... Mountains appear blue(er) than things up close specifically because of raleigh scattering. I drive about 5 miles from two mountain ranges in my normal commute, and when I'm that close to a range, if it's in full sunlight, it just looks slightly hazy. If in shadow (i.e., I'm East of the range, looking West in late afternoon), then the mountains are deep blue and featureless. From personal experience, I'd put 5 miles at the barest minimum of seeing Raleigh scattering effects, but anecdote does NOT equal data. Commented Sep 29, 2018 at 4:02
• @Ghedipunk, that's actually a good observation, but I wonder if it's scattering of the light reflected off the mountains, or caused by the scattered light from the sun that will be reflected. I don't know enough about this effect and it's making me feel like eating ice cream and watching old episodes of Nova.
– JBH
Commented Sep 29, 2018 at 4:39
• @JBH, thinking about it further... It would have to be the reflection of pre-scattered light. Without an atmosphere, shadows are black. It's only because of Raleigh scattering that shadows have any color at all. I eagerly await someone with domain specific knowledge to step in. (And eating ice cream while watching Nova sounds like an great time for me, too.) Commented Sep 29, 2018 at 5:18