NASA is urging skywatchers to head outside early on Jan. 31 for a look at what the space agency is calling a "lunar trifecta."
It's the rare combination of a blue moon (the second full moon in a single calendar month), a supermoon (a moon that's full when it's at its closest point in its slightly elliptical orbit around Earth), and a total lunar eclipse or "blood moon," in which Earth's shadow upon the lunar surface gives it a reddish tint.
What's the best time to view the supermoon?
In the continental U.S., the best views of this "super blue blood moon" will be in the West, Gordon Johnston, a NASA program executive who blogs about the moon from the agency's Washington, D.C. headquarters, said in a written statement.
"Set your alarm early and go out and take a look."
The eclipse, which will also be visible in Alaska and Hawaii as well as in other parts of the world, begins at 5:51 a.m. Eastern Time, as the moon is about to set in the western sky.
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Skywatchers in the eastern U.S. can expect to see only the initial phases of the eclipse before the moon sets. "So your best opportunity if you live in the East is to head outside about 6:45 a.m and get to a high place," Johnson said, adding that it's important to have a clear line of sight to the horizon in the west-northwest.
The period of totality — when the moon is in the darkest part of Earth's shadow — will last a bit more than one and a quarter hours, according to EarthSky.org. There's no need for special viewing precautions. Unlike solar eclipses, lunar eclipses pose no danger to the eyes.
What makes it a supermoon?
Just how special an event will this be? A blue moon isn't actually blue, of course, and blood moons aren't really blood red. As for supermoons, which occur at the point of orbit known as perigee, they're just a tad bigger and brighter than usual.
"The differences between an ordinary full moon and a 'supermoon' are so trivial that the phrase 'supermoon' is essentially meaningless for the general public," Dr. Jay Pasachoff, an astronomer at Williams College in Williamstown, Massachusetts, told NBC News MACH in an email.
"I note that the Earth was closest to the sun on its annual orbit on January 4, as it is every year — so we could have called that day a 'supersun.' Did you notice that the sun was brighter than usual? Of course not."
But this confluence of lunar phenomena really is rare.
Lunar eclipses occur up to three times a year, supermoons about once every 14 months, and blue moons about once every 2.7 years, according to Space.com. NASA says this trifecta will be the first in 35 years. The next won't come until 2037.
