TONIGHT, FULL MOON BIGGEST IN 20 YEARS / NASA VIDEO: SUPER FULL MOON
 

MANILA, MARCH 19, 2011 (CNN) By Ed Payne- If the moon looks a little bit bigger and brighter this weekend, there's a reason for that. It is.

Saturday's full moon will be a super "perigee moon" -- the biggest in almost 20 years. This celestial event is far rarer than the famed blue moon, which happens once about every two-and-a-half years.

"The last full moon so big and close to Earth occurred in March of 1993," said Geoff Chester with the U.S. Naval Observatory in Washington. "I'd say it's worth a look."

Full moons look different because of the elliptical shape of the moon's orbit. When it's at perigee, the moon is about 31,000 miles (50,000 km) closer to Earth than when it's at the farthest point of its orbit, also known as apogee.

"Nearby perigee moons are about 14% bigger and 30% brighter than lesser moons that occur on the apogee side of the moon's orbit," the NASA website says.

This full moon will rise in the east at sunset and should look especially big at that time because of what's known as the "moon illusion."

"For reasons not fully understood by astronomers or psychologists, low-hanging moons look unnaturally large when they beam through trees, buildings and other foreground objects," according to NASA.

Even though it may look close enough to touch, Saturday's full moon will still be at a healthy distance -- some 211,600 miles (356,577 km) away.

As rare as it is, it may be worth a look. Miss it and you'll have to wait until 2029 to see it again.

SUPER FULL MOON

NASA - March 16, 2011: Mark your calendar. On March 19th, a full Moon of rare size and beauty will rise in the east at sunset. It's a super "perigee moon"--the biggest in almost 20 years. [PHOTO - The Moon looks extra-big when it is beaming through foreground objects--a.k.a. "the Moon illusion."]

"The last full Moon so big and close to Earth occurred in March of 1993," says Geoff Chester of the US Naval Observatory in Washington DC. "I'd say it's worth a look."

Full Moons vary in size because of the oval shape of the Moon's orbit. It is an ellipse with one side (perigee) about 50,000 km closer to Earth than the other (apogee): diagram. Nearby perigee moons are about 14% bigger and 30% brighter than lesser moons that occur on the apogee side of the Moon's orbit. Super Full Moon (movie strip, 550px) Above: Perigee moons are as much as 14% wider and 30% brighter than lesser full Moons. [video]link below]

"The full Moon of March 19th occurs less than one hour away from perigee--a near-perfect coincidence1 that happens only 18 years or so," adds Chester.

A perigee full Moon brings with it extra-high "perigean tides," but this is nothing to worry about, according to NOAA. In most places, lunar gravity at perigee pulls tide waters only a few centimeters (an inch or so) higher than usual. Local geography can amplify the effect to about 15 centimeters (six inches)--not exactly a great flood. Super Full Moon (moon illusion, 200px) The Moon looks extra-big when it is beaming through foreground objects--a.k.a. "the Moon illusion."

Indeed, contrary to some reports circulating the Internet, perigee Moons do not trigger natural disasters. The "super moon" of March 1983, for instance, passed without incident. And an almost-super Moon in Dec. 2008 also proved harmless.

Okay, the Moon is 14% bigger than usual, but can you really tell the difference? It's tricky. There are no rulers floating in the sky to measure lunar diameters. Hanging high overhead with no reference points to provide a sense of scale, one full Moon can seem much like any other.

The best time to look is when the Moon is near the horizon. That is when illusion mixes with reality to produce a truly stunning view. For reasons not fully understood by astronomers or psychologists, low-hanging Moons look unnaturally large when they beam through trees, buildings and other foreground objects. On March 19th, why not let the "Moon illusion" amplify a full Moon that's extra-big to begin with? The swollen orb rising in the east at sunset may seem so nearby, you can almost reach out and touch it.

Don't bother. Even a super perigee Moon is still 356,577 km away. That is, it turns out, a distance of rare beauty.

WA5TH NASA VIDEO ON YOUTUBE: http://www.youtube.com/watch?v=r1yalg_Apdw


Chief News Editor: Sol Jose Vanzi

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