At least 2 to 4 times a year, the moon turns red. This is the result of a lunar eclipse, where the Earth is between the sun and moon. So how is it possible that the moon turns red? Well, that's just because the Earth has a red shadow!
The Earth's atmosphere extends about 80 kilometers above the surface and when the sun shines onto the Earth, the atmosphere makes it looks like there's a ring around the Earth. Furthermore, when the sunlight shines through our atmosphere, green, blue and violet light are scattered due to their short wavelength, while the longer waved red light, is barely touched, it's because of this that the sky appears blue during the day.
So what happens to the "barely touched" red light? When the red light enters the Earth's atmosphere, it refracts towards the surface. The light goes around the Earth, refracts again and exits on the other side. So during a lunar eclipse, this red light goes off the Earth and directly onto the moon, giving you a red coloured moon, dubbed 'Blood Moon'.
Thanks for reading!
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http://earthsky.org/space/why-does-the-moon-look-red-during-a-total-lunar-eclipse
https://curiosity.com/topics/what-is-a-blood-moon-and-how-does-it-happen-curiosity/
https://mars.nasa.gov/allaboutmars/nightsky/total-lunar-eclipse/
