text: Air of course we can not see, so at least to humans it seems to be clear. As for the sky...\nhttp://www.sciencemadesimple.com/sky_blue.html\nhttp://www.everything2.com/index.pl?node=Why%20is%20the%20sky%20blue%3F\n\n"Contrary to popular belief the sky is not blue because of refraction.\n\nRefraction is not a significant enough effect to have this sort of affect although it can change the apparent position of the sun\n\nThe real reason why the sky is blue is due to a phenomenon known as Rayleigh Scattering whereby blue light is absorbed by gaseous molecules in the atmosphere ( ie air ) and then re-emitted in a random direction. \n\nThus as white light from the sun travels through the atmosphere the blue light is scattered away from its original direction of travel, and some of it is scattered down towards us which causes us to perceive the sky as blue. \n\nThis is also the reason why the sun is yellow."