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Happy Supermoon! Celebrate lunar largeness as a planetary holiday

The largest full moon of 2013 will rise this weekend. NBC's Brian Williams reports.



The biggest, brightest full moon of the year shines in the sky this weekend, which makes this the perfect time to take in the wonders of the night sky — whether or not you're swept up in the "supermoon" hype.

Some say the supermoon ranks as "one of the biggest celestial events of the year." Meanwhile, Bad Astronomy's Phil Plait says it's no big deal, and that "you'd never notice the difference" between this full moon and any other. The true message of the supermoon lies in a happy medium: It's not a monstrous moon, but it's a great excuse to moon over a monthly sight that we sometimes take for granted.


The moon itself is the same size it's been for ages, but the key is how close it'll be when it's full. Because the moon's orbit around our planet is elliptical, its precise distance varies, depending on where it is in the orbit. This time around, the moon enters its full phase at 7:32 a.m. ET Sunday, only about a half-hour after it passes the point in its orbit nearest to Earth, which is known as perigee. As a result, this full moon will look about 14 percent wider and 30 percent brighter than it does at the farthest point in its orbit.

June's full moon — which you can start looking out for Saturday night — is the headliner because it's this year's best example of a "perigee full moon." Tides will be stronger than usual, but that's nothing to get alarmed about.

The fact that this full moon takes place so soon after Friday's summer solstice adds an extra twist, according to astronomer Bob Berman. "The visual effect is to make this the lowest-down full moon of 2013," Berman said in a news release from Slooh Space Camera. "And since lower moons tend to be orange­, yellow or amber, shining as they do through more than twice as much reddening air and moisture, this lunar experience should give us a true 'honey moon' all night long. Moreover, lower moons look larger, thanks to the famous 'moon illusion.' This second moon­-enhancing effect will be more visually obvious than its actual size increase."

According to the definition used by Farmer's Almanac, we're getting three supermoons this year, including one that took place on May 25 and another that's due on July 22. Neither of those quite matches up to this weekend's moon — and technically speaking, this weekend's supermoon is slightly less super than last year's. However, these differences are truly imperceptible, amounting to mere hundreds of miles one way or the other across a total distance of 221,823 miles (356,991 kilometers). For what it's worth, the 21st century's biggest super-duper-moon will be visible on Dec. 6, 2052.

Why not make each year's biggest full moon a skywatching holiday? Consider it a modern-day spin-off of Japan's traditional moon-viewing parties. If the skies are clear, get yourself outside on Saturday or Sunday to catch the show. While you're at it, make an appointment to look for the International Space Station passing overhead. If the skies aren't clear, you can still join the online crowd watching a virtual moon on the Slooh Space Camera website, starting at 9 p.m. ET Sunday. And whatever you do, give the moon a wink to honor Apollo 11's dearly departed moonwalker, Neil Armstrong.

More about the supermoon:


Alan Boyle is NBCNews.com's science editor. Connect with the Cosmic Log community by "liking" the NBC News Science Facebook page, following @b0yle on Twitter and adding the Cosmic Log page to your Google+ presence. To keep up with NBCNews.com's stories about science and space, sign up for the Tech & Science newsletter, delivered to your email in-box every weekday. You can also check out "The Case for Pluto," my book about the controversial dwarf planet and the search for new worlds.