Why is it called Blood Moon and what causes it?

With November’s longest partial blood moon around the corner, many wonder what causes the moon to go red. Scroll down to find out!

Why is it called Blood Moon and what causes it?
Mike Blake REUTERS

Despite all the creepy myths and legends blaming witches for the blood moon, it’s in fact a lunar eclipse that causes the reddish copper color on our moon.

What causes a lunar eclipse?

Those lunar eclipses can only happen when there is a full moon and the sun is illuminating its surface, but this is not the only thing it takes for a lunar eclipse to happen. For the moon to be red, the planes of the earth sun and moon have to coincide, meaning the earth gets in the middle of the sun and the moon blocks the light and causes an eclipse.

This is a very rare phenomenon as the moon tends to orbit in a different plane than the earth and sun.

However, it could happen that the earth doesn’t entirely block the sunlight, causing the darkest part of its shadow to fall over the moon's surface, this is called a partial eclipse.

Why is it called a "blood moon"?

A totally eclipsed moon can be called a blood moon due to its reddish copper appearance. This phenomenon happens when the only light reflected from the lunar surface has been refracted by the earth’s atmosphere causing raylight scattering, a similar answer to what causes sunsets and sunrises to be red.

Therefore, the moon is named after the color formed by the eclipse.

How red the moon appears depends on different factors, such as pollution, clouds, or recent natural disasters causing dust to rise in the atmosphere.

The more pollution, clouds, or dust is in the middle of human vision and the moon, the darker it seems, whereas clear skies will tend to portray more vivid reds.