Why is the sky sometimes blue and sometimes red?

Question

something about radiation and wavelengths and stuff. i dont know though

Answer 1

sky is blue because molecules in the air scatter blue light from the sun more than they scatter red light.
we see red and orange colours because the blue light has been scattered out and away from the line of sight.

http://math.ucr.edu/home/baez/physics/General/BlueSky/blue_sky.html