Some of the big constellations of autumn begin to push their way into the evening sky this month. Pegasus, the flying horse, is well up in the east at nightfall by month’s end, with Andromeda, the prin- cess, to its left. Under especially dark skies, you should be able to pick out M31, the Andromeda Galaxy. The planet Jupiter is ending its run in the evening sky, and will disappear in the Sun’s glare next month. Another giant planet, Neptune, is at its best for the year, although still far too faint to see with the eye alone.
You are here
In the Sky This Month
September 19: Moon and Aldebaran
A bright star follows the Moon across the sky tonight. That seems appropriate, since its name, Aldebaran, means “the Follower.” The star will stand to the lower left of the Moon as they climb into view, around midnight, and closer to the Moon at dawn.
September 20: Big Galaxy
If you have nice, dark skies, look for the Milky Way crossing the sky this evening. The subtle glow of its myriad stars arcs high across the sky as darkness falls, and drops down the western sky later on.
September 21: Last-Quarter Moon
The Moon is at last quarter tonight. It is three-quarters of the way through its monthly cycle of phases, so it lines up at a right angle to the Earth-Sun line. At that angle, sunlight illuminates half of the lunar hemisphere that faces our way.
September 22: Autumnal Equinox
Day and night will be just about equal the next few days for the entire world. That’s because fall arrives in the northern hemisphere late tonight at the September equinox, which is the moment the Sun crosses the equator from north to south.
September 23: Celestial Sea
Even if you have cloudless skies this evening, a wet view awaits you — a swath of constellations related to water. They’re known as the “celestial sea.” They stretch across the southeast in early evening, and across the entire southern sky by midnight.
September 24: Vulpecula
A hard-to-see fox trots high across the sky on autumn evenings: the constellation Vulpecula. It is small and faint. But it is near the middle of the Summer Triangle, which is outlined by three bright stars.
September 25: Dumbbell Nebula
The Dumbbell Nebula, which represents the last gasp of a dying star, is in Vulpecula, the fox. The constellation is high overhead at nightfall. The nebula is about halfway between Deneb and Altair, the stars that mark one side of the Summer Triangle.