If you’re quick, you might be able to spot this Saturday’s lunar eclipse, which will turn the silvery moon into a bloody red orb for nine to 12 minutes. But look away, and you might miss the sky show—the lunar eclipse will be the shortest on the books for another century.
National Geographic’s Andrew Fazekas reports that this weekend’s blood moon will be the third in a series of four lunar eclipses. This type of tetrad won’t repeat for another 20 years—and Fazekas notes that, though there will be another visible eclipse in September, Saturday’s will be the shortest this century.
Blood moons, in particular, only occur when there's a total lunar eclipse. When Earth’s shadow passes over a full moon’s surface, Earth’s atmosphere filters out a portion of the light spectrum. What remains is a reddish color that’s effectively projected onto the moon. While the eclipse reaches its peak, the moon will go dark gray, but then will take on a reddish or coppery tint that depends on the amount of ash and dust in the Earth’s atmosphere. It's creepy enough that it's sparked its fair share of doomsday theories. And one English historian surmises that Richard III may have been laid to rest under a blood moon in 1485.
Though the total eclipse itself will be short, it will be paired with a long period of partial eclipse—102 minutes, to be exact. Space.com’s Joe Rao explains that because the moon will have recently reached its furthest point from Earth, it will take a “leisurely trek” through the Earth’s shadow due to its slow orbital velocity.