why does the sun go red as it sinks below the sea at sunset?

Answer 1

The angle of refraction due to the atmosphere changes as the sun sets. This allows other colors of the spectrum to be seen other than blue (i.e. red, orange purple, etc)

Answer 2

you are looking through more of earths atmosphere when you look at the sun at that elevation and the atmosphere is like a prism and separates the light in the visible spectrum and red gets through