Rise of the 'Supermoon': Biggest Full Moon in 18 Years Occurs Saturday
by Alex O'Neal,posted Oct 25 2011 2:35PM
Thanks to a fluke of orbital mechanics that brings the moon closer to Earth than that it has been in more than 18 years, the biggest full moon of 2011 will occur on Saturday, leading some observers to dub it a "supermoon."
On Saturday afternoon at 3 p.m. Eastern Daylight Time, the moon will arrive at its closest point to the Earth in 2011: a distance of 221,565 miles (356,575 kilometers) away. And only 50 minutes earlier, the moon will officially be full. [Photos: Our Changing Moon]
At its peak, the supermoon of March may appear 14 percent larger and 30 percent brighter than lesser full moons (when the moon is at its farthest from Earth), weather permitting. Yet to the casual observer, it may be hard to tell the difference.
The supermoon will not cause natural disasters, such as the Japan earthquake, a NASA scientist has stressed.
Spotting the supermoon
The moon has not been in a position to appear this large since March 1993.
In December 2008, there was a near-supermoon when the moon turned full four hours away from its perigee – the point in its orbit that is closest to Earth. But this month, the full moon and perigee are just under one hour apart, promising spectacular views, depending on local conditions. [Infographic: 'Supermoon' Full Moons Explained]
Although a full moon theoretically lasts just a moment, that moment is imperceptible to ordinary observation.
During the day or so before and after, most will speak of seeing the nearly full moon as "full," with the actual shaded area of the lunar surface being so narrow – and changing in apparent width so slowly – that it is hard for the naked eye to tell whether it's present, or which side it is.
Supermoon making waves
In addition, the near coincidence of Saturday’s full moon with perigee will result in a dramatically large range of high and low ocean tides.
The highest tides will not, however, coincide with the perigee moon but will actually lag by up to a few days depending on the specific coastal location. For example, in Wilmington, N.C., the highest tide (5.3 feet) will be attained at 11:21 p.m. EDT on March 20.