Tonight's supermoon is not just the last time the moon is closest to Earth in its orbit this year. It also doubles as a Harvest Moon, the moon closest to the autumnal equinox.
The supermoon appears tonight, reaching full phase around 9:38 p.m. EDT. At this time, it will look bigger and brighter than normal. Because it is the full moon closest to September's equinox, it is also a Harvest Moon.
The Harvest Moon brings an earlier moonrise, because its path in autumn gives it a more narrow angle. This means that the moon is closest to the horizon at sunset, which makes the moon look larger.
This year, though, the harvest moon will look even larger than it normally does, because the moon is also reaching the point where it is closest to Earth. This happens when a full moon coincides with what's called its perigree, or its closest point to Earth in its orbit. This is a supermoon.
However, even with this supermoon also being a Harvest Moon, the biggest supermoon of the year occurred on August 10, when the moon was only a little over 220,000 miles from Earth.
If you have a keen eye, though, and want to catch the supermoon, Geza Gyuk at the Adler Planetarium in Chicago makes a few recommendations.
"A full moon is visible, weather permitting, all night," says Gyuk. "Just find a time that is convenient and where you can spend a few minutes just looking and appreciating."
However, if you look for the moon when its near the horizon, you're more bound to notice the size difference. This is also a good time for photos of the event.
An international team of astronomers are tracking this supermoon from the Canary Islands in Spain, as well as airing a live broadcast of their observations, starting at 8:30 p.m. CDT. Astronomers will also discuss the mythology surrounding the Harvest Moon during the broadcast.
"Whether we call this a super Harvest Moon or a Harvest supermoon, and whether we fuss over the fact that lunar perigee happened just one night before this moon was full, there's no denying that it's the Harvest Moon," says astronomer Bob Berman. "Yet it's bathed in myth and misconception even without all the extra 'supermoon' business. It will be fun to explore the true secrets of the Harvest Moon while watching it live."
