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The real supermoon stands up this weekend


Supermoon at National Harbor, July 12 (Cynthia James via Flickr)

So technically, there are three supermoons in 2014. We had one on July 12, and have yet another on September 9. But the supermoon on August 8 is, in fact, the most “super” of the bunch.

National Geographic is calling it an “extra-supermoon”.

It is the full moon closest to the Earth of the supermoon trio, some 863 miles closer to Earth than July’s “Buck” or “Thunder” moon.

A moon achieves “supermoon” status when it’s both full and within 90 percent of its closet approach to Earth in a given orbit, or near perigee (which means closest point), according to astrologer Richard Nolle, who coined the term.


Supermoon view from National Airport, July 12 (Joe Gruber via Flickr)

The moon will appear 16 percent bigger and 30 percent brighter than in January, when it was furthest away from Earth in its orbit, or at apogee.

Known as the Sturgeon Moon (because of the abundance of the sturgeon in  the Great Lakes and Lake Champlain at this time of year), it becomes full this Sunday, August 10, at 2:09 p.m. EDT, just 26 minutes after coming closest to Earth.  It’s a nearly perfect coincidence.

“Such tight timing won’t occur again until 2034,” says National Geographic.

While the moon officially reaches full phase and cozies closet to Earth Sunday afternoon, it will appear more or less full Friday, Saturday, and Sunday evening for night skywatchers (at 96-99 percent illumination).


Supermoon adjacent to the Washington Monument, July 12 (Jim Knapp via Flickr)

Don’t necessarily expect to notice much of a difference between this full moon and others.

“A 30% difference in brightness can easily be masked by clouds and haze,” says NASA. “Also, there are no rulers floating in the sky to measure lunar diameters. Hanging high overhead with no reference points to provide a sense of scale, one full Moon looks about the same size as any other.”

Geoff Chester, an astronomer at U.S. Naval Observatory, is completely underwhelmed by the so-called “supermoon” phenomenon.

“This is being touted as yet another “Super-Moon” by popular and social media for reasons that I still can’t fathom, but for the most part it is a “non-event” that is almost purely hype,” he writes on his “The Sky This Week” blog.

Chester tells NASA it’s difficult to tell one moon apart from another. The so-called “moon illusion” – in which the moon appears much bigger than it actually is when it sits on the horizon – is what make moons stand out.

“For reasons not fully understood by astronomers or psychologists, low-hanging Moons look unnaturally large when they beam through trees, buildings and other foreground objects,” NASA writes.

Irrespective of the real reasons a moon looks big, Chester admits possible benefit from this supermoon craze: “[I]f it gets people out and looking at the night sky and maybe hooks them into astronomy, then it’s a good thing.”

If you’d like to take a gander, here are the moonrise and moonset times this weekend for Washington, D.C. (from timeanddate.com):

Friday night and Saturday morning: 6:21 p.m. and 4:55 a.m.
Saturday night and Sunday morning: 7:10 p.m. and 6:07 a.m.
Sunday night and Monday morning: 7:55 p.m. and 7:20 a.m.

 

[posttv url="http://www.washingtonpost.com/posttv/national/supermoon-lights-up-night-skies/2014/08/11/ced5e494-2158-11e4-8b10-7db129976abb_video.html" ]

Jason is the Washington Post’s weather editor and Capital Weather Gang's chief meteorologist. He earned a master's degree in atmospheric science, and spent 10 years as a climate change science analyst for the U.S. government. He holds the Digital Seal of Approval from the National Weather Association.
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