Remember last month's massive moon, the one that dazzled onlookers on December 12? That moon was 14 percent larger and 30 percent brighter than a typical full moon.

Well, it's back tonight. NASA says tonight's moon will be the biggest full moon of 2009, "almost identical" to the one on December 12.

Here's what's going on: The moon's orbit of Earth is an ellipse, with one end closer to Earth than the other. Tonight, the moon will be near the closer end of the ellipse, a spot known as the perigee. (Apogee is the more distant end.)

NASA is quite excited about the perigee moon, as you might expect: "You can read a newspaper, ride a bike, write a letter, and at the same time count the stars overhead." (With all due respect to NASA, we would suggest not doing all of those things at the same time.) And tonight's forecast for much of the Northeast is for snow, according to, so it may be too cloudy to see the moon there.

If you don't want to wait to hear about the next perigee moon on 60-Second Science, we're not offended. You can calculate the schedule and be ready.

Update (12:30 a.m. EST): We're gathering photos of the perigee with this other blog post. Send yours!

Photo of perigee (left) and apogee (right) moon courtesy of Galileo Project/NASA