Don't forget to look up tonight! The Harvest moon and the third
"Supermoon" is a nonscientific term for a moon that turns full just as it reaches perigee -- the point in its orbit when it is closest to Earth.
The moon does not travel around our planet in a perfect circle, so there are times when it is closer to us, and times when it is further away.
When the moon is at perigee, it is 31,000 miles closer to the Earth than when it is at apogee, or the point on its orbit when it is farthest from us.
Monday evening's supermoon is the last in a series of three supermoons in a row. We had one on July 12 and another on Aug. 10. On Monday, the moon will turn full at 6:38 p.m., and it will have reached perigee less than 24-hours earlier.
If you can look up at exactly 6:38, you will have the satisfaction of knowing you are seeing the completely full supermoon. But don't feel bad if you miss it. For most of us, the moon looked pretty full last night, and it will continue to look pretty super for another few nights.
Monday's moon is also known as the Harvest moon, because it is the full moon that falls closest to the fall equinox. It got the name "Harvest moon" because of a well-timed coincidence that allows it to give off a little extra light just as farmers are harvesting their crops.
Because of the tilt of the moon's orbit in September, the moon rises about the same time as the sun is setting for a few days after the full moon. Usually the moon rises at sunset only on the day it is full and then rises about an hour later each subsequent day, says Steve Edberg, an astronomer at the
"People are more likely to notice it because it has this effect that looks like it hasn't really changed positions, and it seems like it is hanging around a lot longer," he told the Los Angeles Times in 2011.
So, look up tonight, and look up for the next few nights too. There's a lot of super stuff going on with the moon!