It would appear that the blue sky is actually produced by the solar wind and solar radiation exciting air molecules to emit light, just like a neon lamp!
Steven Magee, Light Forensics
air, astrobiology, astronomical, astronomy, astrophysics, blue, blue-sky, emit, excite, excitement, exciting, lamp, light, molecules, neon, neon-light, radiation, radiation-effects, solar, solar-energy, solar-power, solar-system, wind