Why sky look purple and orange clouds at sunset?
The orange and red tints that the Sun and Moon sometimes take on are caused by the particles in the Earth’s atmosphere. When light (or more specifically, packets of light called photons) from an astronomical object passes through the Earth’s atmosphere, it scatters off of particles in the latter. It turns out that these particles like to scatter blue light more than they do red light; so “bluer” photons (those with shorter wavelengths) tend to get scattered, and “redder” photons (those with longer wavelengths) pass through. So, astronomical objects look redder from Earth than they would from space, because the redder wavelengths from the objects penetrate the atmosphere better than the bluer ones. Incidentally, this is why the sky is blue: blue light from the Sun is scattered in all directions on its way to the Earth.
