June 21, 2013 12:30 pm
This weekend, the Moon will become a Supermoon. And not only that, but this Saturday’s Supermoon will be the most Supermoon-y Supermoon to Supermoon all year. The distance of the Earth to the Moon varies over time. Throughout 2013 the Moon will travel in and out by 30757 miles, around 13% of the average Earth—Moon distance. A Supermoon is a full moon that takes place when the Moon is within the nearest 10% of this drift, and Saturday’s Supermoon will be the nearest-approaching Supermoon all year.
Because the Moon is closer to Earth, the full moon will appear bigger than during other less-super full moons. So, if you’re the kind who likes to watch full moons, this will be a full moon to watch. But the Supermoon moniker is more one of definition than anything to do with particularly striking visuals. On Slate, astronomer Phil Plait runs through—and summarily debunks—a number of super myths about Supermoons. While the Moon will technically be bigger in the sky, he says, you probably won’t actually be able to tell.
Last month, the full Moon happened when it was just over 358,000 kilometers away—only a little bit farther (by about 1 percent) than it will be this month. Even if you compared last month’s full Moon with this month’s “Supermoon” side-by-side you’d hardly notice it; you’d never notice the difference just by going out one month to look, waiting a month, and looking again.
Heck, the difference between the two extremes of apogee and perigee is only about 40,000 km (25,000 miles)—about a 10-15 percent difference overall, making the Moon look 10-15 percent bigger at perigee. Even that wouldn’t be spotted by eye, especially with two weeks separating the two observations.
But, if you’re out and about on the town with your friends this weekend, it certainly can’t hurt to point up to the sky and shout:“It’s a bird! It’s a plane! It’s…. Supermoon!” At worst they’ll think you’re weird, at best you’ll impress your friends with your astronomical knowledge.
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