At sunset, on Saturday, a giant moon rose in the east. It was the biggest and brightest one of 2009, which has certainly amazed even seasoned observers. Earth, the moon and the sun are all bound together by gravity, which keeps us going around the sun and keeps the moon going around us as it goes through phases. The moon makes such a trip around us every 29.5 days, but the orbit is not a perfect circle.
One portion is 50,000 m closer to our planet than the farthest part and, on Saturday night, the moon was at perigee, the closest point to us on this orbit. Therefore, it will appear 14% bigger in our sky and 30 percent brighter than other full moons during 2009, according to NASA. It's interesting to see that a similar turn of events happened in December, making that month's full moon the largest of 2008.
As the moon's position affects tides, they will be higher too, as the moon gets closer. Tides like these are called perigean tides, because they occur when the moon is at or near perigee. A full moon rises right around sunset, no matter where you are.
However, because of the mechanics of all these processes, the moon is never truly 100 percent full. For that to happen, all three objects have to be in a perfect line, and when that rare circumstance occurs, there is, of course, a total eclipse of the moon. Even as we speak, the moon is moving away, by about 4 centimeters an year. Eventually, this drift will force it to take 47 days to circle our planet.