Clouds are white. Like all white objects, they reflect the light that hits them. Shine a red light on paper, it’ll look red.
The air around our planet scatters blue light in all directions, but lets red go straight. The result is that light coming straight at us from the sun looks red or yellow, while light coming scattered from the air makes the sky blue.
So when this filtered red light from the sun goes through a *lot* of air, as happens with sunrise and sunset, it gets very red. Hits a white cloud, and the cloud looks red:
Latest Answers