The Moon appears different colors depending on viewing conditions and atmospheric effects, according to a collection of images featured by NASA's Astronomy Picture of the Day.
Outside Earth's atmosphere, the Moon reflects sunlight as a brown-tinged gray. An astrophotographer documented apparent colors of the full moon over 10 years from different locations across Italy, capturing red, yellow, blue, and purple hues.
Red or yellow moons typically occur when viewed near the horizon, where blue light scatters away through a long atmospheric path, sometimes carrying fine dust. Blue moons are rarer and suggest larger dust particles in the atmosphere. The cause of purple moons remains unclear, possibly resulting from a combination of effects.
The collection includes an image from the total lunar eclipse of July 2018, when the Moon appeared faint red. This coloration occurred because light refracted through air surrounding Earth as the Moon entered Earth's shadow.