NPR Blogs

The Moon Puts On A Triple Super Summer Spectacle

By L. Carol Ritchie

Published July 12, 2014 at 7:42 AM EDT

The moon appeared bigger and brighter when it went supermoon on June 23, 2013 — especially when it was seen next to objects on the horizon, such as the helicopter from the original Batman television show at the New Jersey State Fair last year.

Summer 2014 promises to be more super than most, and not just because of the World Cup or LeBron James returning to Cleveland.

This summer, the moon will reach "super" status not once, not twice, but three times — and the first time happens Saturday night.

A supermoon, or a perigee moon, occurs when the moon turns full just as it hits the spot in its elliptical orbit when it is closest to the Earth, NASA says, a celestial coincidence that will make the orb appear 14 percent bigger and 30 percent brighter than an ordinary full moon.

The next two appearances will be Aug. 10 and Sept. 9, when the moon will be about 30,000 miles closer to the Earth than at its farthest point, or its apogee. The moon will actually be closest on Aug. 10, turning full not only the same day but during the same hour as perigee.

The ScienceCast video below calls that an extra-supermoon. We'd like to call it a super-duper moon.

A supermoon is actually not so rare. It happened three times during 2013, but only one made worldwide headlines, Geoff Chester of the U.S. Naval Observatory told NASA Science News.

"Generally speaking, full Moons occur near perigee every 13 months and 18 days, so it's not all that unusual," Chester said. "In fact, just last year there were three perigee Moons in a row, but only one was widely reported."

The effect is hard to detect, and may only look impressive when seen next to objects on the horizon, said Greg Laughlin, an astronomer at University of California, Santa Cruz. Laughlin told SFGate.com that the brain can only compare the moon visually against objects of familiar size.

"When the moon is high in the sky, you don't have the reference," he said.

"It's a real effect, but it's fairly small," Laughlin said. "It's very difficult to remember how large the last full moon was. You kind of have to take detailed photographs and line up the photographs to see that effect."

In fact, Chester thinks just knowing about the supermoon makes the Earth's satellite seem more magnificent.

"I guarantee that some folks will think it's the biggest moon they've ever seen if they catch it rising over a distant horizon, because the media will have told them to pay attention to this particular one," Chester told NASA Science News.