On Sunday, June 23, at 7 a.m. EDT (1100 GMT), the moon will arrive at perigee — the point in its orbit 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."