Full moon lovers will be in for a treat this summer as the coming months bring not just one, but three full supermoons in a row.
A supermoon occurs when the Moon is at least 90% of the way to its closest approach to the Earth at the same time it is full or new. Supermoons are caused by the shape of the Moon’s orbit, which is not a perfect circle, but an ellipse, or oval, shape. The Moon orbits the Earth once each month, and each month reaches a point farthest from the Earth, called apogee, and closest to the Earth, called perigee.
The reason these two Moon phases are singled out is because each of them means that the Sun, Earth, and Moon are in alignment. When the Moon is full, it sits exactly on the opposite side of the Earth from the Sun. When the Moon is new, it sits between the Earth and the Sun. In both cases, the gravitational pull from these two bodies – the Moon and the Sun – combine to create larger than normal tides, called “spring tides,” on Earth. When the Moon is also at perigee at this time, the effect is magnified into what is called a “proxigean spring tide.”
Of course, a new Moon at perigee isn’t very exciting to look at – because the new Moon does not reflect the Sun’s light, it is invisible – so full supermoons get much more attention than new supermoons. There are usually about four or five supermoon events each year, only about half of which tend to be full supermoons. This year is somewhat unusual in that there are only three supermoons, and all three are full.
May’s full Moon falls on the 25th, one day before the lunar perigee on the 26th. The May supermoon also coincides with a very minor partial lunar eclipse. The largest of this year’s supermoons will occur on June 23, within 22 minutes of the Moon’s perigee on the same day. June’s supermoon coincides with the Moon’s closest approach to Earth until August 10, 2014. Finally, July’s full Moon will rise on July 22, one day after that month’s lunar perigee.
With two or three full supermoons each year, they may not be unusual events, but for those who love looking up at the night sky, any excuse will do.