A lunar eclipse is a beautiful sight.
During a lunar eclipse, Earth's shadow is cast onto the full Moon, causing the Moon to turn a deep, rusty red colour.
Here are some amazing facts about lunar eclipses, what causes them and how to observe them.
You can see Earth's shadow
Normally when the Moon is visible in the sky, it – or part of it – appears bright because sunlight is bouncing off the Moon and reflecting towards Earth (this is also why we see the phases of the Moon).
During a lunar eclipse, Earth is positioned exactly between the Sun and the Moon.
So the darkening that you observe on the lunar surface is actually Earth's shadow, blocking out sunlight.
Lunar eclipses nearly happen every month
A lunar eclipse occurs when Earth is between the Sun and the Moon.
But isn't that what causes a full Moon, too? If so, why do we see a full Moon every month, but not a lunar eclipse every month?
Lunar eclipses only happen at full Moon when the Sun, Earth and Moon are lined up in the exact orientation.
Most months, the Moon moves above or below Earth’s shadow. An eclipse doesn't happen, but we see a full Moon instead.
The Moon turns rusty red
Ever noticed how a sunset makes the Sun – the whole sky even – appear so much redder and more dramatic?
This is to do with the 'scattering' effect of Earth's atmosphere.
When the Sun is low down in the sky, sunlight has to pass through a thicker part of our planet's dense atmosphere.
Blue light is scattered more than red light, and so we see more red light as a result.
Roughly the same thing is happening during a lunar eclipse.
Sunlight travels towards the Moon and hits its surface. But during a total lunar eclipse, Earth is in the way, and that sunlight is bent – or refracted – as it passes through Earth's atmosphere.
Only light that is bent inwards by Earth’s atmosphere makes it to the Moon.
Our atmosphere filters out blue light and leaves red light, giving a total lunar eclipse its rusty red colour.
This is why some call it a 'blood Moon'.
You don't need any fancy equipment
During a solar eclipse, the Moon passes in front of the Sun, and so observing a solar eclipse means looking at the Sun. As a result, eclipse glasses or solar filters must be used to protect your eyesight.
During a lunar eclipse, we're observing the Moon, so no protective gear needs to be worn.
You can observe a total lunar eclipse with the naked eye, but binoculars or a telescope will give you a better look.
It's one way to prove Earth isn't flat
We live in a time in which the claim that Earth is 'flat', and not spherical, seems to be gaining popularity.
Earth is not flat; it's spherical. And one way of proving this is to look at Earth's circular shadow on the Moon during a lunar eclipse.
But couldn't Earth be round and flat, like a disc, and still throw a circular shadow during a lunar eclipse?
The only way a lunar eclipse shadow could always be round is if Earth is spherical, and not flat like a disc.
Hence, the circular shadow of a lunar eclipse is one way of proving Earth is spherical
There's a key to categorising its darkness
You can describe the colour and darkness of the Moon during a lunar eclipse by using the Danjon Scale.
It's named after its creator, the French astronomer André-Louis Danjon, and measures the darkness of an eclipse from L0 through to L4.
If you observe a lunar eclipse, see if you can pinpoint what 'L' value it is.
Find out more via NASA's guide to the Danjon Scale.
If you observe or photograph a lunar eclipse, share your images and experiences with us by emailing contactus@skyatnightmagazine.com
