Much ado has been made about the so-called "supermoon" that will take place tonight. Tonight's full moon will nearly coincide with the moon's arrival at the perigee point in its orbit around the Earth, resulting in the closest and biggest full moon in our sky since March 1993.
Or will it?
On Saturday night, the moon will arrive at perigee at 19:09 UT (3:09 p.m. Eastern Time). Its distance from the Earth at that moment will be 221,565 miles. But just over three years ago, on Dec. 12, 2008, which was also the night of a full moon, the moon reached perigee at 21:39 UT (4:39 p.m. Eastern Time) at a distance of 221,559 miles, about 6 miles closer than Saturday night's perigee distance.
So it seems Saturday night's supermoon will actually be just a little less super than the full moon of Dec. 2008.
Despite this fact, Geoff Chester of the United States Naval Observatory says tonight's full moon is still the winner for closeness of a full moon. How is that possible?
A lunar loophole
Chester points out that on Dec. 12, 2008, the moon reached fullness at 16:37 UT, while perigee was at 21:39. That's a difference of just over five hours. So when the moon turned full that night, it was still five hours away from reaching its closest point to Earth; its distance at the moment it turned full was 221,587 miles. ...
via What Makes a 'Supermoon' So Super? - FoxNews.com.
Enjoy the biggest moon of 2011 tonight.