Eclipses of the Moon occur when the Moon passes into the shadow cast by Earth. They always take place when the Moon is full. They can be seen from anywhere on Earth if the Moon happens to be in the sky at the time. This means that, over time, far more lunar eclipses than solar eclipses can be seen from any particular location.
The Earth's shadow has two parts. The inner part - called the 'umbra' - is uniformly dark. The outer greyish part - called the 'penumbra' - gets lighter towards its outer edge. If the Moon only goes through the penumbra, the dimming can be hardly noticeable.
The Moon is not normally completely dark during an eclipse because some sunlight is scattered towards the Moon by Earth's atmosphere. Usually, the Moon appears a deep coppery-orange colour even during totality. However, the colour and brightness are variable from one eclipse to another. They depend on factors such as the amount of volcanic dust and cloud in the atmosphere at the time.
To make this multiple exposure of a total lunar eclipse, the camera was tracked across
the sky at the rate the Sun moves. It shows up the shape of Earth's shadow,
which is circular but considerably larger than the Moon. Akira Fujii.
A schematic side-on view of a total lunar eclipse, showing
the Moon in Earth's shadow.
The track of the Moon through Earth's shadow during a total eclipse and a partial eclipse. It also shows how the darkness of the penumbra decreases away from the umbra (shaded).