By Dr. Tony Phillips, from Science@NASA
When last month's full Moon rose over Florida, onlooker Raquel Stanton of Cocoa Beach realized that something was up.
"The Moon was stunningly gorgeous--and it looked bigger than usual!" she says. "My whole family noticed and watched in awe."
Like millions of others around the world, she had witnessed the biggest full Moon of 2008--a "perigee Moon," 14% wider and 30% brighter than lesser Moons she had seen before. "I'll never forget it."
Alert: It's about to happen again.
This 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. It's the best kind of déjà vu for people who love the magic of a moonlit landscape.
January is a snowy month in the northern hemisphere, and the combination of snow + perigee moonlight is simply amazing. When the Moon soars overhead at midnight, the white terrain springs to life with a reflected glow that banishes night, yet is not the same as day. You can read a newspaper, ride a bike, write a letter, and at the same time count the stars overhead. It is an otherworldly experience that really must be sampled first hand.
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, 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 catch yourself reaching out to touch it.
You won't be the only one. Even at perigee, the Moon is 360,000 km away, yet the distant beauty beckons to poets, stargazers and NASA with equal force: "Come back," it seems to say, "I'm really not so far away."
Above Image: The perigee full of Dec. 2008. "A cold wind was blowing as the Moon set over a neighbor's farm," says photographer Eric Ingmundson of Sparta, Wisconsin. "Next time (Jan. 10th) I plan to use a tripod."
