The Earth has just one natural satellite, the Moon, which completes a full orbit of our planet in 29 and a half days. Sunlight reflects off the surface of the Moon, making it look as if it gives off its own light. During its orbit, the Moon goes through a number of phases in which different portions of the Moon are visible. It is only possibly for a lunar eclipse to happen when the Moon is full.
The Cause of a Total Lunar Eclipse
The position of the full moon is such that it sits directly opposite the Sun in the sky. It also passes through the Earth‘s shadow. An eclipse is caused when the shadow blocks part or all of the Sun‘s light, depending on the angle at which the Moon is orbiting the Earth.
The shadow of the Earth is divided into two portions: the penumbra and the umbra. The penumbra refers to the two outer sections of the shadow and this does not block all of the sunlight from reaching the Moon. The umbra, or inner portion, blocks all the light. It is when the Moon is covered by the umbra that a total lunar eclipse occurs.
A total lunar eclipse doesn’t happen every time there is a full moon because the Moon’s orbit of the Earth is at a slightly different angle to the Earth’s orbit around the Sun. Therefore the Moon is only in the correct position for a total lunar eclipse to occur at certain points in their respective orbits. The best conditions for this is when the Moon is at the intersection of the two orbits, which happens roughly once every six months.
A Red Moon
The total lunar eclipse is the most striking and breathtaking kind of eclipse due to the intense red colour the moon becomes during the phase of totality – that is, the period when the Moon is completely in the Earth’s shadow.
The Moon appears red because of the indirect sunlight which illuminates it, even when it is fully covered by the shadow of the Earth. Most of the blue light is separated by the Earth’s atmosphere when the sunlight passes through, leaving behind light which is mostly red or orange in colour. This filtered light is not as bright as pure sunlight, but it is this source of illumination that gives the Moon its red glow.
Observing a total lunar eclipse is very straightforward. It isn’t necessary to use any specialist equipment as it is so easy to see with the naked eye – no telescope required. It is also perfectly safe to watch without the use of protective filters, unlike a solar eclipse.