When the full Moon passes through Earth's shadow it dims and, at the deepest stage, glows red — a "blood moon". Unlike a solar eclipse it's completely safe to watch with the naked eye, from anywhere the Moon is up. Here's the next big one.
How a lunar eclipse works
A lunar eclipse happens at full Moon, when the Sun, Earth and Moon fall into a line and the Moon drifts into Earth's shadow. That shadow has two parts: a pale outer penumbra, which only dims the Moon slightly, and a dark central umbra. How deep the Moon slides into the umbra sets the type — a subtle penumbral eclipse, a partial one where a dark bite crosses the disc (this is what August 2026 brings), or a total eclipse with the whole Moon in shadow.
Why the Moon turns red
Even in a total eclipse the Moon rarely goes fully dark — it glows a coppery red, the "blood moon". The only sunlight still reaching it has grazed through Earth's atmosphere, which scatters the blue away and bends the leftover red light inward onto the lunar surface. In effect you're seeing the combined glow of every sunrise and sunset on Earth at once, cast onto the Moon; the more dust and cloud around the planet's edge, the darker and deeper-red the eclipse.
Why not every full Moon — and how often you can watch one
The Moon's orbit is tilted about 5° to Earth's path around the Sun, so most full Moons pass a little above or below the shadow and nothing happens. An eclipse only comes when a full Moon lands near one of the two points where those paths cross — which is why eclipses arrive in "seasons" roughly twice a year. The payoff for skywatchers: a lunar eclipse is visible from the entire night side of Earth at once (a solar eclipse only from a narrow track), and it's completely safe to watch with the naked eye — so over any few years, most places catch several.