WHY ARE SUNSETS RED?
The sky isn’t always blue. When the Sun is low in the sky, at sunrise or sunset, it can take on a red hue. This is explained by the same physics – Rayleigh scattering – as the blueness of the sky at other times. When we look towards the Sun at sunset, we’re seeing light that has travelled further through the atmosphere than when the Sun is high in the sky. Most of the shorter wavelengths have been scattered away, and we just see what’s left. The dramatic phenomenon of a blood Moon, when the Moon turns red during a lunar eclipse, is also caused by sunlight passing through a large thickness of Earth’s atmosphere. It happens when Earth blocks direct sunlight from reaching the Moon – its only source of illumination is light that has already travelled all the way through Earth’s atmosphere.