Why does the Moon turn red?

The reddish color isn't a property of the Moon itself, but of Earth's atmosphere. When the Sun, Earth, and Moon align, our planet casts a shadow that the Moon can enter; if the disk falls completely within the darkest part of that shadow, the eclipse is total. The Moon doesn't disappear: it stops receiving direct sunlight, but remains lit by light grazing the edge of the atmosphere. During the eclipse of March 14, 2025, totality lasted from 2:26 to 3:31 EDT, with the Moon tinted a coppery red.

The atmosphere doesn't filter all colors equally: blue light scatters more because it travels in shorter waves, while red light passes through the air more directly. Dust, pollution, and other aerosols also scatter blue light, so the exact shade of each eclipse depends on the condition of the air that light has crossed. Hence the image NASA uses: it's as if every sunrise and sunset on the planet were projected at once onto the lunar surface.

Lunar eclipses are only possible at full moon, and the alignment doesn't occur every month: there are two eclipse seasons a year, each about 35 days long. At least two partial lunar eclipses occur every year, while total ones are rare. No equipment is needed to see them, though binoculars or a telescope improve the view. And if the Moon looks reddish with no eclipse happening, the cause is different: it's usually low on the horizon, and its light arrives after crossing much more air.