Gaze into the sky shortly before dawn on Wednesday, and you’ll have an opportunity to see an event that hasn't taken place since 1982 – a super blue blood moon.
The name is a reference to a rare celestial hat trick that we're lucky enough to be able to see with the naked eye: a supermoon, a blue moon and a blood moon, all rolled into one.
What's a super moon?
The moon's orbit isn't a circle, it's elliptical. At its furthest point (apogee), its center is 251,968 miles from Earth's, but its closest point (perigee), is just 225,803 miles away. The difference is noticeable. In fact, when there's a full moon at perigee, which is what a supermoon is, it's 14 percent larger and about 30 percent brighter than normal.
Tonight's unique because it's our second supermoon of the month, the first of which occurred on January 1. That means that we're also going to see a blue moon.
What's a blue moon?
It's the term used to describe the occurrence of two full moons in one month. We had a full moon on the first of January and went through the complete lunar cycle (29.53 days). Now, another full moon will fill our sky on January 31.
If you're curious about the history of the term, Smithsonian Magazine has a write up.
What's a blood moon?
The term blood moon is used to describe a total lunar eclipse, or when a full moon crosses completely into the Earth's shadow.
You can see a full moon when the satellite is positioned on the opposite side of the Earth in relation to the sun, its face being lit by our closest star. During a lunar eclipse, the moon, at perigee, has that light obscured by the earth as it lines up perfectly with our planet.
Slowly, over the course of the night, the moon gets darker and darker until it finally turns red. That's because even though the Earth gets in the way of the sun's light, the star is so large that some of the rays travel around our planet, through our atmosphere and onto the moon. When the rays pass through our atmosphere, the shorter wavelengths of blue light are scattered, while the red light, or the longer wavelengths, stay intact, coloring the lunar surface.
All told, the moon will stay completely red for a little more than an hour.
Does this event offer any unique scientific opportunities?
Scientists at NASA will be monitoring changes in the moon's surface temperature as it goes from fully full to totally eclipsed.
"By observing the way the surface heats up and cools off, understanding the thermal properties, that gives us a better understanding of the physical make up [of the moon's surface]," said Jacob Bleacher, a research geologist with NASA.
Over the course of a few hours, the moon will go from being well lit and hot, to shrouded in darkness and cool, before returning to fully lit once again. During that time, different parts of the moon will warm and cool at different rates, depending on the materials being heated. The idea is that as scientists track the temperature changes, they can gain insight into the moon's crust.
According to NASA, the moon can heat up as hot as 253 degrees Fahrenheit and cool to a low of -387 degrees.
"The moon ... is continuously bombarded by objects of various sizes, down to micro meteorites, and that continuous process acts to break up big pieces and churns up and mixes up the small pieces," Bleacher said. "And so, what you consider maybe to be a mature regolith will heat up and cool off in a way that’s fundamentally different than something that’s made up of larger blocks.
"So, if you haven’t had a chance to develop a mature regolith, that could suggest to you that that area is younger. It hasn’t had as much time to be exposed to develop that regolith. And then you can start to think about reasons why that might be."
How can I watch it?
Walk outside and look up, there won't be another event like this until 2037.
The eclipse starts at 3:48 AM. Totality begins at 4:51 AM and ends by 6:07 AM. The sun rises at 6:51 AM.
If you'd like to hang out with a crowd of people, Griffith observatory is also holding an event starting at 3:45 AM.