If skies are clear Saturday, go out at sunset and look for the giant moon rising in the east. It will be the biggest and brightest one of 2009, sure to wow even seasoned observers.
But the orbit is not a perfect circle. One portion is about 31,000 miles (50,000 km) closer to our planet than the farthest part, so the moon’s apparent size in the sky changes. Saturday night (Jan. 10) the moon will be at perigee, the closest point to us on this orbit.
It will appear about 14 percent bigger in our sky and 30 percent brighter than some other full moons during 2009, according to NASA. (A similar setup occurred in December, making that month’s full moon the largest of 2008.)
Tides will be higher, too. Earth’s oceans are pulled by the gravity of the moon and the sun. So when the moon is closer, tides are pulled higher. Scientists call these perigean tides, because they occur when the moon is at or near perigee. (The farthest point on the lunar orbit is called apogee.)
A departing fact: The moon is moving away as you read this, by about 1.6 inches (4 centimeters) a year. Eventually this drift will force the moon to take 47 days to circle our world.
Wow! Go outside tonight and check it out!!