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 princess, to its left. Under especially dark skies, you should be able to pick out M31, the Andromeda galaxy. Venus, the Evening Star, inches higher in the western sky at sunset. And Mars begins to eke away from Antares and Saturn, although they remain fairly close throughout the month.
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In the Sky This Month
September 17: The Colt
Equuleus, the colt, graces the evening sky this month. The tiny constellation looks like a flat-topped pyramid. A couple of hours after sunset, it stands about halfway between the eastern horizon and the point directly overhead.
September 18: Autumn Constellations
As summer comes to an end, the constellations of autumn are moving into prime-time evening viewing hours. The best known are from Greek mythology: Pegasus, Andromeda, Perseus, Cassiopeia, and Cepheus, all of which stand high overhead in mid-evening.
September 19: Vela X-1
Enif, the star at the nose of Pegasus, the flying horse, is in the east at nightfall, to the upper right of the Great Square of Pegasus. The star is about 670 light-years away, so the light we see from it tonight actually left the star in the 1340s.
September 20: Moon and Aldebaran
Aldebaran, the bright orange eye of Taurus, the bull, rises to the lower left of the Moon before midnight, and stands closer to the Moon at first light tomorrow.
September 21: Mu Cephei
The reddest star in northern skies stands high overhead during the evening hours. Its official designation is Mu Cephei, but it is also known as the Garnet Star. It is a red supergiant, which means it is much larger and cooler than the Sun.
September 22: Autumn Skies
The Sun changes hemispheres today. It crosses the equator from north to south, a moment known as the equinox. That ushers in autumn here in the northern hemisphere, and spring in the south.
September 23: Last-Quarter Moon
The Moon reaches last quarter today. Half of the side that faces Earth is bathed in sunlight, while the other half is in darkness. When the Moon is at last quarter it is leading Earth in our planet’s orbit around the Sun.
New Sept. 1 4:03 am
First Sept. 9, 6:49 am
Full Sept. 16, 2:05 pm
Last Sept. 23, 4:56 am
New Sept. 30, 7:11 pm
Times are U.S. Central Time.
Apogee September 6
Perigee September 18
The full Moon of September is known as the Harvest Moon, Fruit Moon, or Corn Moon.