Early Friday morning, the moon will be bathed in a spectacular deep red glow as the Earth casts an enveloping shadow over its rocky counterpart, creating the longest partial lunar eclipse in 580 years.
For lunar devotees, it’s a cherished night. But they may be out of luck this year.
A strong cold front will arrive from the Atlantic Ocean Thursday evening, bringing with it cloud cover and rain that may endure through the eclipse’s end at around 7 a.m. Friday.
“Really by 1 a.m., its pretty much overcast all across New England,” said Matthew Belk, a meteorologist at the National Weather Service’s Norton office. “So unless you want to go to the middle of the Atlantic or up into eastern Canada you’re probably out of luck.”
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The cloud cover will make the moon just about impossible to see, and the only hope may be to head west towards the Connecticut River Valley at around 4 a.m. That’s when the eclipse will peak, and, Belk said, clouds may begin clearing out between 4 and 5 a.m. So there’s a chance, but a small one. And odds of catching the beginning of the eclipse around 1 a.m. are next to none.
It’s a crushing blow for those who have been anticipating the eclipse, which occurs when the Earth, moon, and sun align, casting Earth’s shadow over the moon.
“Definitely a drag,” said JJ Hermes, an assistant professor of astronomy at Boston University.
In Friday morning’s “almost total” case, nearly the entire moon will be coated in shadow, save for about three percent of its craggy southern lip.
“The simplest way to think about it is the Earth’s shadow is getting cast on the moon,” said Hermes. “The sun is where we get all of our light, and the same goes for the moon. That normal white glow is the moon reflecting sunlight. When our planet gets in the way we cast a big shadow.”
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And while a lunar eclipse typically occurs twice a year, this one is particularly rare. It’ll last more than three hours and 28 minutes, according to the National Aeronautics and Space Administration.
Usually, lunar eclipses only last for about two hours. So why is this one so much longer?
“The moon’s orbit around the Earth is not circular,” said Carl Schmidt, a research scientist at BU’s Center for Space Physics. “When [the moon] is at apogee, when it’s farthest from the Earth, the time that it takes it to move across the sky is a little bit slower. It’s near apogee right now, and that’s what gives the eclipse this really long duration.”
Total eclipses are less common, only occurring once every two years.
The real draw for moon-watchers would be around 4 a.m. Friday morning, when the eclipse peaks and the red glow is on full display as the moon is almost completely covered by Earth’s umbra, or full, darkest shadow.
Up to that point, the show may be rather dull. Around 1 a.m., the moon’s glow will begin slowly fading as it passes into Earth’s penumbra, or partial shadow. The red glow that comes after is a result of light from the sun refracting through Earth’s atmosphere.
“Basically, the moon will start to show this very deep red glow,” said Hermes. “What you’re seeing is light passing through Earth’s atmosphere, and you’re basically witnessing all of the sunrises and sunsets on Earth at that moment casting onto the moon.”
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After the peak, Earth’s umbra will begin to shift off of the moon, and the final shadow will slip away at 7:03 a.m., just before the moon disappears from view.
Tonight’s full moon is a Beaver Moon, nicknamed by Native Americans because fall was the time to set traps for beavers, as the creatures were particularly active in these months, according to NASA.
Not to fret if you miss it, moon enthusiasts. A total lunar eclipse, or blood moon, will light up the night sky in May, providing even more awe-inspiring views.
Andrew Brinker can be reached at andrew.brinker@globe.com. Follow him @andrewnbrinker.