Hey, sky fans! I hope you’re getting by okay. It’s been a tough week. Last night, I took my daughter to see the great Colin Hay, whom you might know as the singer from Men at Work. By the time we got out of the theater and were on our way home, it was pretty late. She dozed in the back seat as I drove. From over the overpasses and scrappy houses along the highway, I saw Orion rising.
The last I saw him was in March when those stars disappeared into the dusk. Now, with a bit of an assist from the end of Daylight Saving Time, it’s up in the east nice and early again. Anytime I get to see those stars, those brilliant, bright stars, Betelgeuse, Rigel, his belt, and his sword, I smile. It’s like seeing old friends again, and it fills me with an incredible sense of calm and warmth. Even after the longest, hardest weeks, sometimes it’s all you have, but it’s also sometimes all you need.
Not far away, the Moon was around, too, a fat waxing gibbous. Don’t worry, I didn’t forget: November’s full Moon, which will be in the skies just in time for the 47th anniversary of the launch of Apollo 12 this coming Monday, November 14, is called the Beaver Moon, or sometimes the Frost Moon. It’s called that because it was the last full Moon before things started to freeze over. The last chance for native Americans to trap beavers and use their furs to keep warm through the winter.
I imagine you’ve read by now that this full Moon will be the biggest, brightest, superest in decades. What I’ve seen in the headlines, and man, I love it when the headlines are full of astronomy news, have been a little strange and confusing. I’ve read a couple that say that the Moon will be closer to the Earth than it has been since 1948 and closer than it will be until 2034. This is right and not quite right at the same time. Let’s see if I can make some sense out of this for you, because I was confused enough that I had to look into what was going on. It’s weird having to look into things that you already know the answer to. “What’s two plus two? Gee… let me get back to you after I have a chance to research it a bit.”
So, let’s see. As we’ve talked about before, the Earth orbits the Sun, and the Moon orbits the Earth. People on Jupiter are having the same sort of chat, only about Io and Callisto. There’s always these things always in motion all the time. Something’s always going around something else. As Kepler’s first law of planetary motion tells us, these orbits are somewhat eccentric ellipses, not circles. At the risk of getting to far out into the swamps, a circle is an ellipse with no eccentricity; it’s perfectly even all the way around, while an ellipse is longer in one direction than the other. That lack of evenness is called eccentricity.
What this eccentricity and ellipisitude means is that the distance from the Earth to the Moon isn’t the same all the way around the Moon’s orbit. That distance changes from one spot to the next. If the orbit were a circle, it’d be exactly the distance the whole time. As it turns out we have words for the points in the Moon’s orbit when it’s closest and farthest from Earth. The farthest point is called apogee and the closest is called perigee.
The Moon is at its brightest when it’s full, things that are closer are bigger and brighter than things that are farther, and things that are super are better than things that aren’t. The word supermoon has come to be the used when the Moon is full when it’s closest to the Earth; full at perigee. You get all this, I know.
Okay. This is where things get more interesting. Those headlines are a little, just a little, misleading, but they’re just misleading enough. Some of them leave out that it’s the closest FULL moon since the 1940s. Distances from the Earth to the Moon change along the Moon’s orbit, it’s true, but the distances themselves are constant from one orbit to the next. Pergiee is always about 226,000 miles (364,000 km). The distances aren’t blowing all over the place like leaves and candy wrappers on a windy day. Perigee isn’t 226,000 miles one month, 183,000 the next, and 375,000 miles the next.
In this orbit, the Moon will reach perigee at about 11:00 UTC, which is about 6:00 A.M. U.S. Eastern time, and 3:00 A.M. on the west coast. After that moment, the Moon starts to inch further away from the Earth until it reaches apogee and the cycle goes on.
The exact moment of the Moon’s fullness, when the Moon is exactly at opposition, the Sun-Earth-Moon is line has the Moon exactly, precisely, opposite the Sun, is just before 14:00 UTC (9:00 A.M. U.S. Eastern, 6:00 A.M. Pacific), less than three hours after perigee. After that moment, it’ll start to wane away until it’s a new Moon again, and that cycle goes on.
It’s that arrangement, that time difference that matters here. Since these moments of perigee and fullness happen so close together, closer than at other full Moons, by the time Moon rises into your night’s sky after sunset on Monday, it will appear that much brighter than even other supermoons.
There it is. It’s not that the Moon itself will be closer next week than it has been in decades. It’s that this full Moon happens when Moon is closer to the Earth than any other full Moon has been since the last time the Cleveland Indians won the World Series, and the closest until the Boise Dodgers win.
I hope you’re able to see it. It should be a big, gorgeous sight; a glorious thing to see rising. I’m going to head out to find a good patch of eastern exposure if I can. I hope you can, too. It’ll actually look big and pretty close to full for the next couple of nights, too, so if you can’t get out Monday, you can get a sneak preview tonight and tomorrow. It’ll even be close for a couple days after it’s full, though… then it’s not a preview anymore. Thanks for stopping by, and clear skies, everyone!