Perigee is when the Moon is closest to the Earth in its orbit around us. Saturday night happens to be “the” night for this year. The moonrise will be the biggest and brightest of 2009. According to NASA, a similar situation occurred last month, making it the largest of 2008.
It takes 29.5 days for the Moon to make a full trip around Earth. And just like Earth’s orbit around the Sun, it’s not a perfect circle. One portion is about 31,000 miles closer (perigee) to us than the farthest part (apogee), so the Moon’s apparent size in the sky changes. It will appear 14 percent bigger and 30 percent brighter than some other full moons in 2009. At moonrise, the Moon appears even larger than it does later in the night when it’s higher in the sky. This illusion, scientists can’t fully explain but think it may have something to do with our perception of things on the horizon compared to stuff overhead.
Earth’s oceans are pulled by the gravity of the Moon and the Sun, so the tides are higher when the Moon is closer, also called perigean tides.
Because of all of the mechanics of the Moon’s orbit, it never truly is 100 percent full. For that to happen, the Sun, Earth and Moon would have to be in a perfect line, and when that rare circumstance occurs, there is a total eclipse of the Moon. That makes my brain hurt trying to make sense of it–to be 100 percent full, yet it ends up a total eclipse. Ouch.
An interesting bit of information about our Moon: it’s moving away from the Earth at 1.6 inches per year. Eventually this drift will force the moon to take 47 days to orbit the Earth.
Now you’re a little smarter, Girlfriend — And so am I.