For much of the country, September is a perfect time for some evening skywatching. The nights are longer and cooler but not yet frigid, and there’s plenty to look at. The Summer Triangle remains in good view high in the sky, while Scorpius and Sagittarius wheel across the southwest. In the east, Pegasus, Andromeda, and Perseus climb into view after sunset.
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In the Sky This Month
September 18: Distant Galaxy
M31, the Andromeda galaxy, is about 2.5 million light-years away, in the constellation Andromeda. Under dark skies, it is just visible as a hazy smudge of light. It is the farthest object that most people can see with their eyes alone.
September 19: Moon and Mars
Mars stands close below the Moon as darkness falls tonight. Although it has faded a good bit since its peak in July, the planet still looks like a bright orange star.
September 20: M15
M15, one of the brightest globular clusters, is high in the southeast this evening. It consists of hundreds of thousands of stars squeezed into a region of space only a few light-years across. It is an easy target for binoculars
September 21: Autumn
Fall arrives in the northern hemisphere this weekend. It’s the autumnal equinox, which is the point at which the Sun crosses the equator from north to south. It occurs at 8:54 p.m. CDT Saturday.
September 22: Fomalhaut System
Fomalhaut, the leading light of Piscis Austrinus, the southern fish, is quite bright. It rises to the lower right of the Moon tonight, and stands below the Moon around midnight. It’s in a fairly barren region of sky, which makes it easier to pick out.
September 23: Harvest Moon
The Harvest Moon lights up the sky the next few nights. It’s the full Moon closest to the fall equinox, which was yesterday. The Moon will be full at 9:52 p.m. CDT tomorrow night. But it will look almost the same on the nights before and after that.
September 24: Moon in the Sea
The Moon is swimming through the Celestial Sea, a group of constellations with a watery theme. Tonight, the Moon is near the border between Aquarius, the water bearer; Pisces, the fishes; and Cetus, the whale or sea monster.