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Oh my god, on the last day of January we’re going to experience a SUPER BLUE BLOOD MOON! I don’t know what that is but it sounds scary as fuck. It might have something to do with the CBS cop drama Blue Bloods, possibly viral marketing in which we will all look into the sky at a certain time and see an enormous Tom Selleck mustache descend over the full moon.
Okay, that’s (probably) not going to happen. In fact, it’s just going to be a lunar eclipse, but that’s still pretty cool so I wanted to tell you about it.
A lunar eclipse is sometimes known as a “blood moon” due to the orangey-red coloring the moon can sometimes take on. A lunar eclipse happens when the Earth, moon, and sun are all in a single plain, with the Earth in between the two. The Earth casts its shadow on the moon, which is one of many ways that ancient astronomers knew the Earth is a sphere — they could see the rounded edge moving over the moon’s face.
But a shadow isn’t always black. Lunar eclipse colors can vary, from very dark to bright red, due to the light from the sun filtering through the Earth’s atmosphere. That’s the same reason why sunrises and sunsets are red, so a poetic way to think about it is that the moon turns red due to all the sunsets and sunrises happening simultaneously on Earth.
So that explains the “blood” part of “super blue blood moon,” but if the moon is going to turn either black or red, where does the “blue” come in? Well, that’s because it is also a “blue moon,” aka the second full moon in the month. I should note that that isn’t the “original” definition but it is the current accepted definition, and it happens once every three years or so. Prior to that definition, a blue moon was determined to be the “extra” moon in a year that had 13 instead of 12. The exact moon that was called a “blue” was the third of four moons that happened in a single season, since a single season usually would have three moons. Why the third instead of the fourth? Because humans are bizarre creatures who make no sense.
We’ve covered “blue” and “blood,” so how about “super?” Well, that’s another un-scientific term that has caught on amongst the general population, used to refer to a moon that is about as close to Earth as it can get. The distance from the Earth to the moon varies, and each lunar cycle the moon is reaches apogee (furthest away) and perigee (closest). When the perigee is really close (there’s no exact distance in the definition), we call it a super moon because again, humans are weird little creatures.
So there you have it: a super blue blood moon. Not as exciting once you break it all down, but remember that eclipses are cool no matter what, and this will be a great time to introduce friends, family members, and especially kids to the wonders of the universe. Space.com set up a nice resource with lessons you can teach any age, so get out there and learn something while enjoying a cool spectacle! The best views will be on the west coast of the US, where it’ll start around 4:30am on January 31. Everyone else can tune into a NASA livestream. Enjoy!