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Published: 2016-10-28 08:49:00
Updated: 2016-10-28 09:31:14
Posted October 28, 2016
By Tony Rice
The moon’s orbit around the Earth isn’t circular, one side of that orbit (perigee) is about 30,000 miles closer than the other (apogee).
When a full moon occurs within 90 percent of that closest approach, astronomers call the phenomenon “perigee-syzygy of the Earth-moon-sun-system,” or perigee full moon, but everyone else just calls it a supermoon.
Each supermoon is a coincidence in the moon’s orbit. The end of 2016 is full of these coincidences, with supermoons occurring with the full moons of Oct. 16, Nov. 14 and Dec. 14.
The Nov. 14 supermoon is arguably an extra-super-moon because the moon is at its fullest at 9:52 a.m. and its closest to Earth, closest of the year, about 2.5 hours earlier.
Extra-super isn't super enough, though. Let’s call this a super-duper-moon because it’s the closest to date in the 21st century. The full moon won't orbit closer for another 18 years. Even that November 2034 only beats this November’s super-duper by about 40 miles, less than the distance from Raleigh to Fayetteville.
December’s supermoon is going to be a super-spoiler. The brightness of a full moon will reduce the visibility of December’s Geminid meteor shower. While it’s difficult to detect much of a size difference in a super moon, that reduced distance does increase the brightness of the moon by about 30 percent. That’s enough to wipe out the view of the faint Geminids.
Do set a reminder for those evenings though. The “moon illusion,” or optical illusion which tricks our brains into seeing the moon as huge near the horizon and much smaller in the vast emptiness overhead. That illusion should be even more spectacular for the super-duper-moon.
Tony Rice is a volunteer in the NASA/JPL Solar System Ambassador program and software engineer at Cisco Systems. You can follow him on twitter @rtphokie.