blood moon

A blood moon refers to what the moon looks like during a total lunar eclipse. A total lunar eclipse occurs when Earth moves between the sun and the moon and thereby shields sunlight from directly reaching the surface of the moon. Some sunlight will still pass through Earth’s atmosphere and as it passes through the long, dense portions of the atmosphere (just like it does at sunset), longer wavelengths of light (which we see as red) will hit the lunar surface making the moon appear red.