Total lunar eclipse: the blood Moon

Inside Earth's shadow

Earth casts a long shadow into space with two parts: a faint outer penumbra and a dark inner umbra. In a total lunar eclipse the Full Moon moves entirely into the umbra. The event unfolds slowly, with the partial phases before and after each taking about an hour, so you can watch the shadow creep across the lunar surface.

Unlike a solar eclipse, everyone on the night side of Earth sees it at the same moment. If the Moon is above your horizon, you are in the audience.

Why the Moon turns red

Even inside the umbra the Moon does not vanish. Sunlight passes through Earth's atmosphere, which bends it inward and filters out blue light, much as at sunrise. The remaining reddish light falls on the Moon, giving the popular name blood Moon.

How deep the colour looks depends on dust, clouds and volcanic ash in our air at that time. A clean atmosphere gives a bright orange Moon, and a dusty one can turn it dark brown.

How to watch

• Use your eyes first. No equipment is needed, and a dark spot away from streetlights helps.
• Add binoculars. They reveal the shadow's edge and the colour gradations.
• Try a camera. A tripod and a long exposure capture the red Moon with stars nearby.
• Dress warmly and bring a chair. The whole event takes several hours.

Safe for everyone

A lunar eclipse only dims the Moon, so you can look at it with bare eyes, binoculars or telescopes, and nobody needs special glasses. This contrasts sharply with a total solar eclipse, where eye protection is essential except during totality. For the version where only part of the Moon darkens, see the partial lunar eclipse.

Old stories and symbols

A reddened Moon was read as an omen in many cultures, sometimes as a wounded or swallowed Moon. Astrology treats it as a time of culmination and release. Both are traditions, and they say more about people than about the sky. Compare all types on the eclipses hub.