The Harvest Moon will be full this month on Saturday Sept. 10 at 5:59 a.m. Eastern Time (0959 Universal Time), according to the U.S. Naval Observatory (opens in new tab) — two days after making a close approach to Saturn.
From New York City, the officially full moon will be visible just before it sets at 6:29 a.m. and rise that evening at 7:45 p.m., according to timeanddate.com (opens in new tab). The moon will be in the constellation Pisces.
A full moon is when the moon is on the opposite side of the Earth from the sun. The moon's orbit is tilted about 5 degrees from the plane of the Earth's orbit, so though the moon is "behind" the Earth, it isn't in the Earth's shadow each time it circles our planet. The occasions when it does fall into the Earth’s shadow we see a lunar eclipse, but that isn’t the case this time (the next lunar eclipse isn’t until November 8).
Observers in mid-northern latitudes will see the moon higher in the sky compared to the summertime — from New York City it will be 40 degrees above the southeastern horizon at exactly midnight (opens in new tab). On the night of Sept 10-11. The full moon of August was a full 10 degrees lower. As the year progresses the moon (for Northern Hemisphere observers) appears to get higher in the sky, corresponding to the sun getting lower at local noon. The reverse happens in the Southern Hemisphere.
What is the Harvest Moon?
The name of the full moon closest to the autumnal equinox, "Harvest Moon," of course reflects that September was the beginning of the harvest season in the Northern Hemisphere, especially in Europe.
Native people in North America had a number of different associations and names for the September lunation and full moon. According to the Ontario Native Literacy project, the Cree peoples called it the Rutting Moon, because elk in September start to rub the velvet off of their antlers ahead of the mating season, while the Ojibwe called it the Falling Leaves Moon. The Cherokee called it the Nut Moon, for when many trees start bearing them. In the Pacific Northwest the Tlingit called the lunation of September the Young Animals Moon, while the Haida called the month "Cedar Bark for Hats and Baskets."
In the Southern Hemisphere September is in the spring, with the days getting warmer, it's no surprise that the Māori of New Zealand described the lunar months in August to September as Mahuru: "The Earth has now acquired warmth, as well as vegetation and trees," according to the Encyclopedia of New Zealand (opens in new tab).
For Abrahamic traditions the full moon of September can be important, as for Jewish people it's the one that precedes the High Holy Day of Rosh Hashonah which starts on Sept. 25. Muslims use a lunar calendar, so the full moon is in the middle of the month (in this case, called Safar). One peculiarity of the Islamic calendar is that the months migrate through the year, relative to Gregorian dates, because the lunar month is shorter than the 30-day month used in solar calendars.
In China, the full moon of September will mark the mid-Autumn Festival, also known as the mooncake festival (for the eponymous food). It is a three-day public holiday (from Sept. 10-12) when families traditionally gather; the festival celebrates the harvest and light lanterns to wish for future prosperity. The festival is also popular in Vietnam, Taiwan, Hong Kong and Macau.
On Sept. 8 the moon makes a close pass to Saturn, with the two in conjunction – having the same celestial longitude – at 6:31 a.m. Eastern Time. That’s just after sunrise in New York City, which is at 6:29 a.m. The pair becomes visible again after sunset (which is at 7:16 p.m.) The closest approach the two bodies will make is about 3º 43’, or about seven and a half lunar diameters. By the time they rise (for Eastern Seaboard sky watchers) they will be a bit further apart, as the moon moves approximately one of its own diameters every hour. That said, the moon and Saturn will be in Capricornus, a faint constellation that can get largely washed out by the light of the moon itself, so if you are looking to the southeast on Sept. 8, Saturn will likely be among the first “stars” you see above and to the right of the moon.
On the night of the full moon, Venus will be a morning star, rising in New York at about 5:36 a.m. Eastern Time. That leaves jut under an hour before sunrise (6:31 a.m. on Sept. 10) so the planet will still be quite low – about 4.5 degrees above the horizon – when the sky starts to get lighter.
Mars, meanwhile, rises at 10:58 p.m. in New York on Sept. 10, and is in the constellation Taurus. By about midnight both the planet and the brightest star in Taurus, Aldebaran, will be in the east-northeast with Mars to the left (north) of Aldebaran. Mars gets quite high in the sky – 70 degrees by the time the sun comes up on Sept. 11. Jupiter, meanwhile, rises at 7:56 p.m. and is visible throughout the night, appearing to the left of the full moon.
The constellations visible in late September are still largely those of summer; early in the evening the Summer Triangle asterism (or star pattern) is still visible near the zenith and Scorpius and Sagittarius will be in the south. As the night of Sept. 10 progresses one will see the summer stars set and the fall stars rise; by midnight Scorpius and Sagittarius have set and the Summer Triangle is above the southwestern horizon. Meanwhile high in the sky to the south is Pegasus, the winged horse, Andromeda and Cetus, the whale.
Editor's Note: If you take an amazing photo of the Harvest Moon that you'd like to share for a possible story or image gallery, send images and comments in to email@example.com.
For more information about the observing the moon, check out "Moongazing: Beginner’s guide to exploring the Moon (opens in new tab)" by the Royal Observatory Greenwich and "The Moon: A Beginner's Guide to Lunar Features and Photography (opens in new tab)" by James Harrop.