The largest full moon of 2013, a so-called “supermoon,” will light up the night sky this weekend, but there’s more to this lunar delight than meets the eye.
On Sunday, June 23, at 7 a.m. EDT (1100 GMT), the moon will arrive at perigee — the point in its orbit bringing it closest to Earth), a distance of 221,824 miles (356,991 kilometers). Now the moon typically reaches perigee once each month (and on some occasions twice), with their respective distances to Earth varying by 3 percent.
But Sunday’s lunar perigee will be the moon’s closest to Earth of 2013. And 32 minutes later, the moon will officially turn full. The close timing of the moon’s perigee and its full phase are what will bring about the biggest full moon of the year, a celestial event popularly defined by some as a “supermoon.”
You can watch a free webcast of 2013 supermoon full moon on SPACE.com on Sunday at 9 p.m. EDT (0100 June 24), courtesy of the skywatching website Slooh Space Camera.
While the exact time of the full moon theoretically lasts just a moment, that moment is imperceptible to casual observers. The moon will appear full a couple of days before and after the actual full moon most will speak of seeing the nearly full moon as “full”: the shaded strip is so narrow, and changing in apparent width so slowly, that it is hard for the naked eye to tell in a casual glance whether it’s present or on which side it is.
During Sunday’s supermoon, the moon will appear about 12.2 percent larger than it will look on Jan. 16, 2014, when it will be farthest from the Earth during its apogee.