Friday, January 9, 2009

Perigree Moon

Last month's full Moon over many viewpoints was particularly radient, and it looked bigger than usual. That's because it was the biggest full Moon of 2008 a perigee Moon, 14% wider and 30% brighter than the smallest full Moons of the year.

It's going to happen again at the beginning of 2009.

On Saturday night, Jan. 10th, another perigee Moon is coming. It's the biggest full Moon of 2009, almost identical to the one that impressed onlookers in Dec. 2008.

Johannes Kepler explained the phenomenon 400 years ago. The Moon's orbit around Earth is not a circle; it is an ellipse, with one side 50,000 km closer to Earth than the other. Astronomers call the point of closest approach "perigee," and that is where the Moon will be this weekend.

Perigee full Moons come along once or twice a year. 2008 ended with one and now 2009 is beginning with another.

Another magic moment happens when the perigee 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. This weekend, the "Moon illusion" will amplify a full Moon that's extra-big to begin with because of the Parigree

At perigee, the Moon is only 360,000 km away!

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