What causes a red moon?

A red moon occurs when the Earth eclipses the moon from sunlight. The moon looks red due to dispersed light from Earth's sunrises and sunsets that is refracted back onto the moon's surface.

As the sun shines its light rays toward Earth, many of the rays are absorbed into the atmosphere. Those rays that are not absorbed are reflected back off of the Earth. Blue light rays scatter when beamed into the Earth, which is the reason the sky is blue. Red light, however, is refracted around the Earth. When there is a total lunar eclipse, those red light rays are aimed at the moon, giving it a reddish glow.