Lunar Eclipse

Lunar Eclipse
Credit: Tomruen

An eclipse is when an object passes through the shadow of another. A lunar eclipse occurs when the Moon moves through the shadow cast by the Earth

It's safe to look at a lunar eclipse. Although the Moon is in the Earth's shadow, some sunlight reaches it. (It's the Sun's light reflecting off its surface which makes the Moon shine). This light has passed through the Earth's atmosphere, which removed the bluest light. This is why the Moon looks a red-brown colour during an eclipse. Lunar eclipses last up to 4 hours! This is because the Earth's shadow is bigger than the Moon.

A lunar eclipse only happens at full moon. This is when the Earth and Sun are on opposite sides of the Earth. Our diagram shows what happens during a lunar eclipse. There are two types of lunar eclipse: 

  • Total lunar eclipse 
  • Partial lunar eclipse. 

We call the darkest part of the shadow, the 'umbra'. It is the dark cone-shaped shadow in the diagram. A total lunar eclipse is when the whole Moon is in this part of the shadow. During a partial lunar eclipse, only part of the Moon is. 
 

Lunar Eclipse Geometry
Credit: Tom Ruen