Every so often, the Moon takes on a deep, coppery red colour in the night sky. This dramatic sight is often called a "blood moon", and although it looks mysterious, it is completely harmless. It happens during a total lunar eclipse.
A lunar eclipse occurs when the Earth moves directly between the Sun and the Moon. The Earth blocks the sunlight and casts a long shadow, and the Moon slowly slides into this shadow. You might expect the Moon to disappear into darkness, but instead it glows red.
The reason lies in our atmosphere — the layer of air around the Earth. As sunlight passes through this air, the air scatters away most of the blue light and bends the remaining red light inwards. This red light is projected onto the surface of the Moon, giving it its unusual colour. In a way, you are seeing the light of every sunrise and sunset on Earth falling on the Moon at once.
Unlike a solar eclipse, a lunar eclipse is perfectly safe to watch with the naked eye. No special glasses are needed — just a clear sky and a good view. Because a blood moon can be seen from anywhere on the night side of the planet, millions of people often look up at the same moment, sharing one quiet, remarkable event.
