This post first appeared on NASA’s ‘Astronomy Image of the Day’ page.
What color is the Moon? It depends on the night. Outside of the Earth’s atmosphere, the dark Moon, which shines by reflected sunlight, appears a magnificently brown-tinged gray. Viewed from inside the Earth’s atmosphere, though, the moon can appear quite different.
A red or yellow-colored moon usually indicates a moon seen near the horizon. There, some of the blue light has been scattered away by a long path through the Earth’s atmosphere, sometimes laden with fine dust.
A blue-colored moon is rarer and can indicate a moon seen through an atmosphere carrying larger dust particles.
What created the purple moon is unclear––it may be a combination of several effects.