Following the part of the Moon in the penumbra and or the umbra of the Earth, lunar eclipses can be classified into different categories:
- Penumbral lunar eclipses occur when Moon passes partly or completely into the Earth’s penumbra, but no part of the Moon is in the umbra. Each lunar eclipse begins and ends with a period of penumbral eclipse.
- Partial lunar eclipses occur when the Moon penetrates partially into the Earth’s umbra.
- Total lunar eclipses occur when the Moon passes entirely through the Earth’s umbra.
The Moon does not completely darken as it passes through the umbra because of the refraction of the sunlight by the Earth’s atmosphere into the shadow cone. Consequently, during a total lunar eclipse, the Moon takes on a reddish color instead of being completely dark.
The size of a lunar eclipse is measured by the fraction of the lunar disk diameter covered by the shadow or penumbral shadow, which is not the same number as the lunar disk area covered by the Earth’s shadow.