On Jan. 31st, 2018, a blue moon and a total lunar eclipse occured in tandem. The result of these celestial events colliding was a fairly rare occurance: an extra full moon in the month coinciding with a lunar ecplise, which as been nicknamed the blood moon for its often deep red coloring. The eclipse two years ago, visible over North America, was the first total eclipse of a blue moon in the region in 150 years, according to EarthSky.org. Blue moons and blood moons each have their own unique influences in culture, especially blood moons. But what are they? Are blue moons really that rare? Does a blood moon signal apocalyptic events for the poor humans here on earth and should people take care venturing out at night in a world lit crimson by the bleeding moon above? What are some popular blood moon superstitions? Let’s find out.

Blue Bloods

Understanding what made the 2018 event so unique requires getting a handle on basic moon movement relative to the Earth and sun. First up? Blue moons. As noted by Space, a blue moon is “the appearance of an additional full moon within a given period.” Historically, the blue moon referred to the rather infrequent occurrence of a third full moon in a season with four full moons, but the modern definition refers to a second full moon in one calendar month, said Space. This helps explain the phrase “once in a blue moon” to mean a rare occurrence.

It is worth noting that the moon rarely turns blue during a blue moon. According to NASA, “Most Blue Moons look pale gray and white, indistinguishable from any other Moon you’ve ever seen.” The next blue moon is scheduled to appear on Halloween, October 31. 2020.

A blood moon, meanwhile, is simply the result of a total lunar eclipse, which puts the moon entirely in Earth’s umbra — the darkest part of its shadow. Although no sunlight can directly reach the moon during a total eclipse, light still passes around the edges of the Earth’s atmosphere and is subject to what HyperPhysics explains is Rayleigh scattering; since blue light scatters more than red light, the moon takes on a reddish cast. The term “blood moon” may also refer to a sequence of four total lunar eclipses that happen within two years, known as a lunar tetrad, said NASA. The last tetrad occurred through 2014-2015 and the next won’t happen until 2032-2033.

Moon Madness

While a blue moon and a blood moon occuring at the same time is rare, blood moons themselves are more common. In fact, a lot of mythology has developed around them. Allen Kerkeslager, associate professor of theology and religious studies at Saint Joseph’s University in Philadelphia, told Live Science that when blood moons occur, it’s hard for us to overcome the “evolutionary tendency to try to explain this as the result of some kind of intentional action by some personal agent.”

Popular blood moon superstitions include:

• The Blood Moon Prophecy — In 2014, Live Science reports that several evangelical Christian ministers forwarded the idea of a “blood moon prophecy,” predicting that the 2014-2015 tetrad would incite a “world-shaking” event. It didn’t pan out.
• “Crazy” Behavior — As noted by Seeker, the full moon has long been associated with “crazy” behavior. Doctors and police officers often have anecdotal stories about working shifts during a full moon. Supposedly the blood moon enhances these effects, but there’s no evidence to back up either claim.
• Starting Anew — According to Refinery 29, those of Wiccan faith consider any blood moon which occurs in October to be “a compelling time to build, to begin, to create” and also a good time to shed old habits. This is also called a “harvest moon” which isn’t a true lunar eclipse but shifts red because of changing seasons.
• Mythology — Cultures from all over the world have different explanations for lunar eclipses, according to National Geographic. “Marauding demons, murderous pets, and ravenous jaguars are just some of the culprits that cultures around the world have blamed for the moon’s disappearance during lunar eclipses.”

So what is a blood moon? It is a total lunar eclipse often colored red thanks to light scattering through atmospheric dust, but it’s also the subject of stories, speculation and superstitions — take your pick.

Does learning about astronomy fascinate you? If so, consider making a career out of it.