A clear cloudless day-time sky is blue because molecules in the air scatter blue light from the sun more than they scatter red light. When we look towards the sun at sunset, we see red and orange colours because the blue light has been scattered out and away from the line of sight.
Thats the simple answer, but there were varying theories, some of them partially right...however, Einstein sussed it in 1911, it's the Nitrogen and Oxygen molecules in the air, are the ones responsible for defracting the red light...not dust as was though possible.
Naturally, I researched this, to expand upon my original understanding...so to bluff your way, mention the first paragraph, then mention the Tyndall effect, then say that Einstein sussed it in 1911. There is more too it, but..like...arssed!
