A Moon that actually looks blue, however, is a very rare sight. The Moon, full or any other phase, can appear blue when the atmosphere is filled with dust or smoke particles of a certain size: slightly wider than 900 nm. The particles scatter the red light, making the Moon appear blue. This is known as Mie scattering and can happen for instance after a dust storm, a forest fire, or a volcanic eruption. Continue reading Moons of May