# Why does the red light from Sun bend towards the moon during the total lunar eclipse?

During the total lunar eclipse the earth, moon and the sun are in perfect alignment so that the moon is within the umbral shadow of the earth. However, instead of turning invisible the moon actually turns red. This is explained in this YouTube video. The short wavelength blue light is said to be scattered away by the earth's atmosphere while the longer wavelength red light is bend towards the moon making it look red. Why doesn't the red light scatter away but instead bend inwards?

The refractive index of the air depends on the density so we get a refractive index gradient from $$n = 1.0003$$ at the surface up to $$n = 1$$ in space, and when a light ray travels in a refractive index gradient it is refracted in the direction of increasing refractive index i.e. downwards towards the ground.