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Moon swings to perigee – closest point – on August 30

The moon's apparent size in our sky depends on its distance from Earth.  The supermoon of March 19, 2011 (right), compared to an average moon of December 20, 2010 (left).  Image by Marco Langbroek of the Netherlands via Wikimedia Commons.

Tonight is Aug 31, 2015

Moon Phase Courtesy U.S. Naval Observatory

The moon reaches perigee – nearest point to Earth in its orbit – on August 30, 2015, at 15:24 Universal Time. This perigee comes less than one day after the moon reached the crest of its full phase on August 29 at 18:35 UT. The close coincidence of the August full moon with perigee brought this full moon close enough to Earth to be dubbed a supermoon.

A supermoon is a particularly close full or new moon. But was this August full moon the closest full moon of 2015? No. Next month, in September 2015, the much closer conjunction of full moon and perigee will give us the closest supermoon of the year on September 28.

View larger. | At right, the August 29, 2015 supermoon at exactly the time (18.36 UT) when it was full. At left, the March 5, 2015 'micro-moon' - smallest full moon of the year.  Photos by Peter Lowenstein in Mutare, Zimbabwe.

View larger. | At right, the August 29, 2015 supermoon at exactly the time (18.36 UT) when it was full. At left, the March 5, 2015 ‘micro-moon’ – smallest full moon of the year. Photos by Peter Lowenstein in Mutare, Zimbabwe.

Full moon and perigee will both occur on September 28, only about one hour apart. The September perigee comes at 1:46 UT while the full moon occurs at 2:51 UT. Of the 13 perigees in 2015, the September perigee will present the closest perigee of the year. Quite commonly, the perigee falling the closest to full moon features the closest perigee of the year. Sometimes the year’s closest perigee is called proxigee.

So we’ll have the most super supermoon of the year on September 28, 2015.

And by awesome coincidence we’ll also have a total eclipse of the moon, lasting for a grand total of 72 minutes. Moreover, a partial eclipse will take place a little over one hour before and after totality. That means, from start to finish, the moon will take some 3 hours and 20 minutes to swing through the Earth’s dark shadow. Yay supermoon!

Moreover, this total lunar eclipse of the September 28 supermoon will feature the fourth and final eclipse of a lunar tetrad – four total lunar eclipses in row, spaced at six lunar months (full moons) apart, with no partial lunar eclipse in between. Some people refer to the full moons of a lunar tetrad as Blood Moons.

Image credit: NASA. The moon's orbit is closer to being a circle than the diagram suggests. The moon is closest to Earth in its orbit at perigee and farthest away at apogee.

Image credit: NASA. The moon’s orbit is closer to being a circle than the diagram suggests. The moon is closest to Earth in its orbit at perigee and farthest away at apogee.

Two months from now, in October 2015, we’ll have yet another supermoon because of another close pairing of full moon and perigee. Perigee will occur on October 26 at 12:59 UT, and the full moon crests on October 27 at 12:05 UT. That’s close enough to give us the third and final full-moon supermoon of the year.

Bottom line: On August 30, 2015, the moon swings to perigee, its closest point to Earth for the month. The center of the moon will come to within 358,290 kilometers (222,631 miles) of the center of the Earth!

Moon at perigee and apogee: 2001 to 2100

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