Jimmy Westlake: Here comes a super-duper moon
We have a full moon every month. There’s nothing unusual about that. Full moons have been happening every 29 1/2 days since time immemorial.
Sometimes, two full moons will fit into one calendar month and the second one is dubbed a “blue moon.” Unusual? Yes — blue moons happen about every two and a half years — but still nothing to get all that excited about.
And, due to its lopsided orbit around the Earth, the moon swings in to its closest point, called perigee, once every month, then swings out to its farthest point, or apogee, about two weeks later. Happens every month, so nothing special about that either.
But, when the full moon and the lunar perigee happen on the same night, well, that is something special. The result is a full moon that appears 7 percent larger than your average full moon and 14 percent larger than the puny little apogee full moon. Once a year, the monthly full moon nearly coincides with the moon’s monthly perigee, producing what has become known as a “super moon.”
On the night of Nov. 13-14 this year, the moon will reach its perigee just 2.4 hours before the moon is full. According to the website EarthSky.org, this near coincidence of full moon and perigee will result in the closest approach that the moon has made to the Earth since Jan. 26, 1948 — 221,524 miles.
That means anyone younger than 68 has never seen a full moon this big. Now, that’s what I call a “super-duper” full moon.
Before you get too excited, we are only talking about a few hundred miles closer than average — a tiny percentage of the moon’s total distance. The unaided eye could not detect that small difference. But, when compared to the size of an apogee full moon, or mini-moon, a super moon appears about 14 percent larger in diameter and about 30 percent larger in area and brightness. That is big enough to detect with the unaided eye.
The sun’s gravity tugging on the moon causes its orbit to shift a little each time around so that super moons occur about a month and a half later each year. That pushes the next super moon into January 2018, but you’ll have to stick around until Nov. 25, 2034, if you want to see a full moon that is more super-duper than the one coming up.
So, if you are looking for an astronomical thrill, the likes of which no one has felt for at least 68 years, step outside and gaze at the super-duper full beaver moon Sunday night. You’ll be closer to the moon than you’ve ever been.
Professor Jimmy Westlake teaches astronomy and physics at Colorado Mountain College’s Steamboat Springs Campus. His “Celestial News” column appears weekly in the Steamboat Today newspaper. Check out Jimmy’s new “2017 Cosmic Calendar” of sky events on his website at jwestlake.com. It features twelve of his best astro-photos and a day-by day listing of cool celestial events that you and your family can enjoy watching all year.
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