Sky gazers will be able to set eyes on a supermoon between Thursday evening and Friday morning this week. The uncommon phenomenon, which occurs roughly three to four times per year, will be the last supermoon until next fall.
Supermoons occur when the moon is both full and is at its closest point to Earth in its orbit, per NASA. They can appear around 14 percent bigger than a full moon at its farthest point from Earth and 30 percent brighter than the dimmest moon, according to the Natural History Museum in London. Still, it can be tough to distinguish a supermoon from a standard full moon just by looking at it.
As the moon orbits the Earth every 27.3 days, it moves in an elliptical shape, so its distance from our planet changes as it travels. At its farthest point, called the apogee, the moon is 251,000 miles away, compared to 226,000 miles at its perigee, or closest point. When a full moon is within 90 percent of its perigee, it qualifies as a supermoon, per NASA.
This week’s supermoon will first appear after sunset Thursday night and reach its peak brightness at close to 6 a.m. Eastern time on Friday, write USA Today’s Claire Thornton and Doyle Rice. The moon will be joined in the sky by Saturn, which will appear about an hour before moonrise, and Jupiter, which will trail the full moon by 90 minutes, per Time’s Jeffrey Kluger.
Have you seen the supermoon yet?— EarthSky (@earthskyscience) September 28, 2023
Tonight, look for the bright, round full supermoon rising in the east at sunset. It’ll glow highest in the sky near midnight, and drop low in the west before sunrise on September 29.
As the full moon occurring closest to the Northern Hemisphere’s autumnal equinox, Thursday’s event is known as a harvest moon. The equinox fell on September 23 this year, when the sun passed from being slightly above the Earth’s equator to slightly below.
Harvest moons get their name because they traditionally were an aid to farmers collecting their crops, per the Farmer’s Almanac. The bright full moon would provide extra light as workers gathered the last of summer’s bounty.
“In the days before tractors with headlights, having moonlight to work by was crucial to getting the harvest in quickly before rain caused it to rot,” Alan MacRobert, an editor at Sky & Telescope, tells USA Today. Modern technology allows today’s farmers to work faster and avoid harvesting into the night, according to Space.com.
This year’s previous supermoons were a buck moon in July and sturgeon and blue moons in August, per Axios’ Jacob Knutson. The Algonquin people chose these names because bucks sprout new antlers and sturgeon fish were more easily caught at these respective points in the summer, per NASA.
As for the blue moon, that term is unrelated to the natural satellite’s color. It simply refers to the second full moon in a month. But the overlap of a blue moon and a supermoon is rare—according to NASA, it occurs once per ten years on average. The next blue supermoon won’t come around until 2037.