VERY occasionally, the sky is lit up by the moon appearing to turn red in a phenomenon known as a blood moon.
These extravagant moons are rare, spectacular events -which leave stargazers giddy with excitement.
Why is the moon red?
The moon appears blood red during a total lunar eclipse.
That's because although the Earth's shadow blocks sunlight from illuminating the moon's surface, some sunlight still reaches the lunar surface indirectly via the Earth's atmosphere, bathing the moon in a red glow.
It has no special astronomical significance – but makes for a really striking view.
The last time the moon went red – known as a blood moon – was in January 2019.
It coincided with a supermoon and the Full Wolf Moon, earning the title Super Blood Wolf Moon.
What causes a blood moon?
A blood moon is caused by an effect known as Rayleigh scattering.
This is possible because while the moon is in total shadow, some light from the sun passes through Earth's atmosphere and is bent toward the moon.
The only light that can be seen is refracted through the earth's shadow, and this light looks red just like with the sunset.
What is a lunar eclipse?
A lunar eclipse is when the Earth's shadow blocks the sun's light, which otherwise reflects off the moon.
There are three types of eclipse – total, partial and penumbral.
A total eclipse sees the Earth's shadow completely cover the moon.
The next full lunar eclipse won't be until May 16, 2022 – though there will be a partial one on November 19, 2021, which will be visible in North and South America, Australia and parts of Europe and Asia.
When has the moon turned red in the US and UK?
The term "blood moon" first emerged in around 2014 when a lunar tetrad occurred – four consecutive total eclipses in a series.
Since then, these are the occasions the moon has turned red:
- April 15, 2014
- October 8, 2014
- April 4, 2015
- September 28. 2015
- August 18, 2016
- August 7, 2017
- January 31, 2018
- January 20, 2019
- May 26, 2021
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