Throughout history, lunar eclipses have seemed dramatic. The Moons grey-white disc deepens to yellow and orange and finally a dark red cast this gives a lunar eclipse its nickname of the blood Moon.
Cultures across the world have thought of the lunar eclipse as a sign of changing fortunes or even ill fortune. The ancient Mesopotamians thought the lunar eclipse was an assault on the king and installed proxy kings during the lunar eclipse so no harm came to their rulers. The Hupa and Luiseño tribes of California thought that the Moon must be injured or sick during the lunar eclipse.
A total lunar eclipse will be visible from parts of Australia, Asia and the western parts of North and South America on May 26. This coincides with a supermoon a point where the full Moon is closest to Earth.
What is a lunar eclipse?
The physical causes of the lunar eclipse are more straightforward than illness, injury or bad luck. A lunar eclipse takes place when the Moon moves into the Earths shadow. The Earth has to be directly between the Sun and the Moon, and a lunar eclipse can only take place during a full Moon.
First, the Moon moves into the penumbra the part of the Earths shadow where not all of the light from the Sun is blocked out. Part of the Moons disc will look dimmer than a regular full Moon.
Where things get interesting and strange is when the Moon moves into the Earths umbra, where direct light from the Sun is totally blocked out by the Earth. This means the only light reflecting off the Moons disc has already been refracted, or bent, by the Earths atmosphere.
A lunar and a solar eclipse.Shutterstock/Alhovik
Blue light is refracted and scattered more by the atmosphere. While all wavelengths of light travel at the same speed, when they pass through a different material – such as passing from the vacuum of space to Earths denser atmosphere – the shorter, bluer wavelengths are refracted and scattered more because of their higher frequency.
This refraction and scattering mean that only longer wavelengths of light reach the Moon and are reflected back to Earth. Red light has a longer wavelength than blue light, which gives the lunar eclipse its characteristic reddish colour. On Earth, we see the same effect during sunrises and sunsets, when the sky has a more reddish glow than during the day.
During a total lunar eclipse, the whole of the lunar disc enters the Earths umbra, so lucky Moon gazers will be able to see a full, reddish Moon. This wont last forever, though. After about 14 minutes, the Moon will move out of Earths umbra and back into its penumbra. In total, the lunar eclipse will last a few hours.
Read more:
Blood moon: lunar eclipse myths from around the world
How to watch the eclipse
Unfortunately, in many places including the UK, the Moon will be below the horizon. However, some institutions will be streaming live feeds of the lunar eclipse from their locations. For example, the Griffith Observatory in Los Angeles will be streaming the whole lunar eclipse for free.
The Moon moves into the Earths penumbra at 10:45am BST, and moves into the Earths umbra at 12:11 BST. Even though you cant necessarily go out stargazing in the dark, you can still follow the eclipse from the comfort of your own home no late nights or early starts required.
Moon gazers will have a while to wait until the next lunar eclipse. On November 19, there will be a partial lunar eclipse thats just about visible, low in the sky, with barely any of the Moon in the Earths penumbra. But many may have better luck next year on May 16 2022, when there will be a total lunar eclipse, visible from the UK in the small hours.
