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What are lunar eclipses and why do they occur?

In the night between May 15 and May 16, a total lunar eclipse will be visible from a wide area of the world. This event will be visible from Europe, North and South America, Africa and parts of Asia. In the UK, we will be able to see the whole of the total phase, from the first contact with the Earth’s penumbra to the full eclipse, between 2:32am and 4:29am. When the Moon leaves the umbra, it will be below the horizon.

What are lunar eclipses?

Lunar eclipses have the striking effect of turning the moon red. But what exactly are they? Well, a lunar eclipse occurs when the Moon moves through the Earth’s shadow, in the same way that a solar eclipse happens when the Earth passes through the Moon’s shadow.

Lunar eclipses are rare because they can only occur when, 1) there is a Full Moon, and 2) the Sun, Earth and Moon are aligned.

Why is the Moon red during a lunar eclipse?

During an eclipse, Earth doesn’t completely block out the sun; If you were lucky enough to be standing on the Moon’s surface at this time, you would see the black disk of Earth with a ring of light around it. The reddish colour of our satellite is caused by some sunlight passing through our atmosphere and being refracted before getting to the Moon’s surface.

Light travels in waves, and different colours have different wavelengths. Blue and green light have a shorter wavelength, which causes them to scatter more easily by the dust and clouds on Earth’s atmosphere. Red light has a longer wavelength, which helps it travel through the atmosphere more easily and hit the Moon’s surface, providing it with that dramatic red glow.

What happens during a lunar eclipse?

There are two kinds of lunar eclipses: a total eclipse occurs when the Moon and Sun are on opposite sides of Earth; during a partial eclipse, only part of Earth’s shadow, or umbra, covers the satellite.

During a lunar eclipse, the Moon will gradually move into the Earth’s shadow as it makes its way through the sky. The light from the sun will be refracted by our atmosphere and dye the Moon red when it hits its surface; the more clouds and dust on Earth’s surface during the eclipse, the redder the Moon will appear.

The total phase of the eclipse will occur when the Moon and the Sun are on opposite sides of the Earth, meaning our satellite is right in the middle of Earth’s umbra. As the Moon keeps moving through the sky, it will slip out of Earth’s umbra, go through Earth’s penumbra (penumbral eclipse) and, finally, leave the shadow completely.

When will the next lunar eclipse happen?

Want to keep an eye out for the next total lunar eclipse? Here’s when we can expect them in the next few years:

  • 15-16 May 2022
  • 7-8 November 2022
  • 13-14 March 2025
  • 7-8 September 2025
  • 2-3 March 2026


Keep track of celestial events with 2022 Guide to the Night Sky, a practical guidebook covering January to December 2022.