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.
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In the Sky This Month
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.
September 26: Milky Way, Dolphin
The Milky Way cuts the sky in half on autumn evenings. In the southeast, look for Delphinus, the dolphin. It is a distinctive little constellation swimming below the Milky Way, just to the left of Altair, the brightest star in Aquila, the eagle.
September 27: Winter Preview
You can already get a preview of the evening skies of winter in the hours before sunrise. Highlights include the constellations Orion and Gemini, along with Sirius, the brightest star in the night sky, all of which are high in the sky at first light.
September 28: Venus Returns
Venus is trying to climb into view in the evening sky. The planet is very low in the west at sunset and sets well before twilight fades. It’s the brightest object in the sky other than the Sun and Moon, though, so it’s worth a try.
September 29: Moon and Venus
The planet Venus will stand to the lower right of the Moon shortly after sunset tonight, looking like a bright star just above the horizon. Venus will climb into better view by late next month, when it will reign as the “evening star.”