Rayleigh scattering is the name given to the effect where the path of light is changed. Sunshine ‘white light’ containing all the colours we can see (and lots of things we can’t see too). When the light from the Sun hits the atmosphere, some of it is deflected around, it doesn’t keep travelling in the same direction. Blue is affected more by this scattering effect than red light. This effect is what causes the sky to be blue. Red light is less affected and this is why during a sunrise or sunset the Sun appears to go ‘redder’. The light reaching your eye when the Sun is low is travelling through a lot more air to reach you than when the Sun is overhead and as a result this light is has to go through more Rayleigh scattering. All this extra scattering means that by the time you see it, red light is almost all that is left. Stars, the Moon, planets, anything that you view through the atmosphere is affected by this process.
Here is a photo of the Moon when it had just risen one night, this wasn’t during a lunar eclipse it was this red purely because of the effects of Rayleigh scattering.