If the full Moon seems unusually large and luminous Saturday night, it’s because our crater-covered satellite will be nearly as close to Earth as possible.
Full Moons vary in size because of the shape of the Moon’s orbit. The Moon follows an elliptical path with one side — the “perigee” — about 30,000 miles closer than the other — the “apogee.” Full Moons that occur on the perigee side of the Moon’s orbit seem extra big and bright.
The scientific term for the phenomenon is “perigee moon.”
NASA says this coincidence will happen s three times in 2014. On Saturday and again on Sept. 9, the Moon becomes full on the same day as perigee. On Aug. 10 it becomes full during the same hour as perigee, making it an extra-super Moon.
“Generally speaking, full Moons occur near perigee every 13 months and 18 days, so it’s not all that unusual,” said Geoff Chester of the U.S. Naval Observatory. “In fact, just last year there were three perigee Moons in a row, but only one was widely reported.”
In practice, NASA says, it’s not always easy to tell the difference between a supermoon and an ordinary full Moon. A 30 percent difference in brightness can easily be masked by clouds and haze.
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