National Geographic News
A ''supermoon,'' or lunar perigee, as seen from West Yorkshire, United Kingdom.

A supermoon rises over West Yorkshire in the U.K. last year.

Photograph from Back Page Images/Rex Features/AP

Andrew Fazekas

for National Geographic News

Published May 3, 2012

On Saturday night, the full moon will be closer to Earth than at any other time this year, an occurrence that's been labeled a supermoon.

Due to the moon's egg-shaped orbit, there are times when our natural satellite is at perigee—its closest to Earth—and at apogee, its farthest.

The term "supermoon" was coined in 1979 to describe a full moon that coincides with perigee—something that happens about once a year, on average.

(See pictures of last year's supermoon.)

During this week's perigee, the moon will be 221,801 miles (356,955 kilometers) from our planet, and that close approach will happen within minutes of the official full moon phase, which occurs at 11:35 p.m. ET.

"As a consequence, this translates into it appearing as much as 16 percent bigger and 30 percent brighter than other full moons of 2012—not a huge amount, but definitely noticeable," said Geza Gyuk, an astronomer at the Adler Planetarium in Chicago.

The moon's proximity won't have any major effects on our planet, according to astronomers, who hope to dispel fears that the looming lunar orb causes natural disasters.

"While we know that during new and full moons the tides are greatest—and if it's in concert with a storm surge it might produce unusual flooding—there is no scientific evidence that earthquakes and other natural disasters are connected," Gyuk said.

(Related: "Titanic Sunk by 'Supermoon' and Celestial Alignment?")

"Supermoons have been happening for billions of years, and nothing particularly special occurs on these dates—except, of course, for a beautiful full moon."

Another Supermoon on the Horizon

For photo hounds, the most picturesque moments during Saturday's supermoon will occur in the minutes after local sunset, as the full moon hovers above the horizon.

"What you should see is the moon rising, deeply colored and looming over the foreground objects," Gyuk said. (Related pictures: See how a lunar eclipse turns the full moon red.)

Because the size of the moon's orbit varies slightly, each monthly perigee is not always the same distance from Earth.

In March 2011, for example, sky-watchers were treated to the closest supermoon in two decades, when the moon was a mere 221,565 miles (356,575 kilometers) from Earth.

(Also see "'Dark' Supermoon Tomorrow: New Moon Gets Closest to Earth.")

And next month the full moon will again roughly coincide with perigee, albeit one that puts the moon a bit farther away, at 222,750 miles (358,482 kilometers), Gyuk said.

"The full moon will appear to be just half of one percent different in size," Gyuk said. "So if you miss this month's supermoon, don't worry, you can see it again when it is only one percent less bright."



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