On July 27, some people get a rare celestial treat: the longest total lunar eclipse of the century. As the Earth snuggles into perfect alignment between the moon and sun, its shadow will completely cover the moon. Rather than appearing as a black spot in the heavens, however, our sole natural satellite will exude a blood-red hue.
Yes, it's the blood moon. And while skywatchers today will look up to the heavens in awe (if they're in the right spot), people long ago took a change in lunar hue as a sign of doom — a good reason to panic.
For instance, folklore suggests that Christopher Columbus knew a lunar eclipse would happen on Feb. 29, 1504, and used this to his advantage.
Read more here: LiveScience