The moon shines over Wisconsin's Lake Winnebago in January.
Photograph by Marti Kallas, My Shot
Published August 24, 2010
It's true, the moon may be shrinking. But that's not why tonight's full moon will be the smallest and faintest of the entire year.
At 2:00 a.m. ET on August 25, the moon will be at apogee, the farthest it will get from Earth as the natural satellite travels in its egg-shaped orbit around our planet. At its closest, the moon is said to be at perigee.
Perigee and apogee each happen about once a month. But the moon wobbles as it orbits, which means its exact distance at those events varies over the year. The moon's phase can also be different during each apogee and perigee.
The moon officially turns full at 1:05 p.m. ET today. The August full moon is sometimes called the sturgeon moon or the green corn moon, according to Native American tradition. (Take a moon myths and mysteries quiz.)
A few hours later the moon will be at apogee—252,518 miles (406,389 kilometers) away from Earth.
The closest—and thus biggest and brightest—full moon of the year occurred on January 30, when the celestial body was 221,577 miles (356,593 kilometers) away.
"The full moon of January was about 50,000 kilometers [31,068 miles] closer to the Earth than the moon [will be] on August 24," said Raminder Singh Samra, resident astronomer at the H.R. MacMillan Space Centre in Vancouver, Canada.
"This results in the moon appearing about 12 percent smaller in [perceived] size as compared to the moon at perigee."
Smallest Full Moon Means Weaker Tides
The biggest influence of the moon on Earth is its tidal force, Samra pointed out. The moon's gravity tugs on our planet, causing the globe to bulge slightly around the middle and driving the ocean tides. (Find out how tidal forces can create volcanoes on other worlds.)
This force will be 15 percent weaker than usual tonight because of the moon's distance, but the effect will be subtle.
"The only people that might notice this are those who are frequently on the oceans," Samra said.
Keen sky-watchers may also notice that our celestial neighbor looks slightly more demure than usual.
"For the regular sky-watcher, it may not be noticeable at first, but photographs or views through a telescope or binoculars will show the full moon as being a bit smaller than what you might have been accustomed to," Samra said.
(Find out how to take part in International Observe the Moon Night next month.)
Next year's biggest and brightest full moon will be on March 19, 2011, while the next farthest-and-smallest moon will be on October 12, 2011.
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