The full moon of October, called the Hunter's Moon, will grace the skies on Oct. 9, the same day that the planet Mercury reaches its highest altitude in the pre-dawn sky, and a day after it reaches greatest elongation (separation) from the sun.
That means on the night of the full moon Mercury will be visible before sunrise and at an altitude high enough to make it easier than usual for observers in mid-northern latitudes.
The moon becomes officially full on Oct.9 at 4:55 p.m. EDT (2055 UTC), according to the U.S. Naval Observatory. For New York City observers, the moon will rise on that day at 6:34 p.m. local time and set the next morning at 7:41 a.m. Rising about 9 minutes after sunset (which will happen at 6:25 p.m.) the moon will be in the constellation Pisces, the fish. Pisces is not an especially bright constellation so it will be largely outshined by the moon itself, as the glare tends to render many nearby objects hard to see.
Given that it is autumn in the Northern hemisphere, the moon will reach a maximal altitude — also known as crossing the meridian — of about 55 degrees in New York City at about 1:01 a.m. on Oct. 10. As one moves south the moon's altitude will increase, until it reaches a maximum near the equator, before losing altitude again as one moves south. In Miami, for example, the moon reaches 70 degrees at 1:27 a.m. on Oct. 10, when it crosses the meridian there.
In Quito, the moon (which technically becomes full at 3:55 p.m. local time on Oct. 9) crosses the meridian on Oct. 10 at 12:20 a.m. and reaches an altitude of 83 degrees. Moving further south, to Buenos Aires, the full moon's maximum elevation on Oct. 10 will be 49 degrees.
Mercury greatest elongation
Mercury will reach its highest altitudes for Northern Hemisphere observers on Oct. 9 and 10. From New York City, on Oct. 10, Mercury rises at 5:26 a.m., while the sun rises at 6:59 a.m. That means by sunrise the planet will be 17 degrees high, according to in-the-sky.org. The planet will be magnitude -0.6, a bit brighter than the star Vega. Civil twilight, which is when the sun is 6 degrees below the horizon and the sky is getting light, is at 6:34 a.m. At that point, Mercury will be about 12 degrees high just south of east.
Mercury will be in the constellation Virgo; to find it one can look for the "sickle" shape of stars that marks the head of Leo the lion, which will be high in the east, and looking below it towards the horizon. Mercury will make a rough triangle with Regulus to the right and Denebola to the left, with Mercury marking the point at the bottom.
From more southern latitudes Mercury will be harder to observe; from Quito, for example, it will only be 15 degrees above the horizon at sunrise, and from Buenos Aires, it will be even lower — about 7 degrees.
Other visible planets in October
Jupiter is visible almost all night; the Moon makes a close approach to the planet, passing 2 degrees south of it on Oct. 8 at 2:11 p.m. Eastern. By the next day, the planet will be to the right of the full Moon. On Oct. 9 Jupiter rises at 5:54 p.m. in New York and sets the next morning at 5:46 a.m. Jupiter is in Pisces, and its steady bright light will be easily spotted among the fainter stars of the Fish.
Saturn rises in the afternoon in New York, at about 4:07 p.m., and sets at 2:06 a.m. the morning of Oct. 10. Saturn is, like Jupiter, in a faint constellation that makes the planet itself more distinct. Saturn will be about 30 degrees above the southern horizon by 10 p.m. From mid-northern latitudes, Saturn will form a rough line with Jupiter and the moon across much of the southern sky, with Saturn on the right (west) and the moon on the eastern side.
October stars and constellations
At about 10 p.m. on Oct. 9, the Summer Triangle is still visible, but it is in the western half of the sky, with Deneb, the brightest star in Cygnus the Swan the highest of the three stars that make up the asterism. Below and to the right of Deneb will be Vega, in Lyra the Lyre, and Altair, the "eye" of the Eagle, to Vega's left. Meanwhile, moving left (towards the south) one will see Fomalhaut, the alpha star in Piscis Austrinus, the Southern Fish. Fomalhaut will be below and to the left of Saturn.
Looking towards the East, Capella, in Auriga, the Charioteer, will be rising, as it ushers in the winter stars. Turning further north and upwards from Capella, the "W" of Cassiopeia is visible, which points one to Polaris, the Pole Star, in Ursa Minor. While there are no "pointers" in Cassiopeia as there are in the Big Dipper, if one draws a rough line from the middle peak of the "W" to the left and downwards, one will reach Polaris. The Big Dipper, meanwhile, will be close to the horizon and will become more prominent as the hours pass.
How the "Hunter's Moon" got its name
The October full moon is often called the Hunter's Moon, according to the Old Farmer's Almanac, because that moon occurs when the season for hunting many game animals begins. Traditional names for the full moon often reflect local environment and history; according to the Ontario Native Literacy Coalition, the Ojibwe people called October's full moon the "Mskawji Giizis," or the Freezing Moon, because October is when the first frosts occur in their traditional territory in the Great Lakes region. The Cree people called it "Pimahamowipisim" (Migrating Moon), as in North America, many bird species start migrating south for the winter in mid-autumn.
In the Pacific Northwest, the Tlingit called the October full moon "Dís Tlein" (Big Moon), while the Haida called the moon "Kalk Kungaay," or the Ice Moon, according to the "Tlingit Moon and Tide Teaching Resource" published by the University of Alaska Fairbanks.
For traditional Chinese calendars, Oct. 9 is in the 9th lunar month, called Júyuè or Chrysanthemum Month, as it is when the flower of that name tends to bloom. The full moon will also mark the start of the Jewish holiday of Sukkot, which is when traditionally the Israelites were called to make a pilgrimage to the Temple in Jerusalem. Jewish people sometimes celebrate by building a temporary structure (called a sukkah) in which meals are served; sometimes people sleep in them to commemorate the temporary homes Jews lived in during their time in the desert after the escape from Egypt.