The stars of autumn begin to push those of summer out of the way as the nights grow longer and cooler. Pegasus is in view in the east as night falls, with several related constellations following the flying horse into the sky over the next few hours.
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In the Sky This Month
September 20: Harvest Moon
The Harvest Moon lights up the sky tonight. It is the full Moon closest to the autumnal equinox. Many people think the Harvest Moon looks especially big and bright. On average, however, it is no flashier than any other full Moon.
September 21: Vega
Vega, one of the brightest stars in the night sky, passes high overhead early this evening. From the middle latitudes of the United States, in fact, it passes directly overhead — a point in the sky called the zenith.
September 22: Autumn Equinox
Today is the autumnal equinox. The Sun crosses the equator from north to south, beginning a season that will last until the winter solstice, in December. The seasons are reversed in the southern hemisphere, where today marks the start of spring.
September 23: Vulpecula
The constellation Vulpecula, the fox, stands high in the south and southeast at nightfall. It is surrounded by the Summer Triangle, which is defined by the stars Vega, Deneb, and Altair. The fox is so faint that you need dark skies to see it.
September 24: Mother and Daughter
Cassiopeia the queen and her daughter Andromeda are in the northeast this evening. Cassiopeia looks like a sideways letter M or W. Andromeda is an indistinct spray of stars spreading to the right of Cassiopeia.
September 25: Moon and Aldebaran
The star Aldebaran, the bright “eye” of Taurus, the bull, rises below the Moon late this evening and follows the Moon across the sky. Aldebaran is a cool, bloated star, so it looks both bright and orange as seen from Earth.
September 26: Sending a Message
Pegasus, the flying horse, is climbing across the night sky. It’s in the east as night falls. It’s preceded by Equuleus, the little horse, to the upper right of Pegasus. Equuleus is the smallest of all the constellations passed down from the ancient world.
New September 6, 7:52 pm
First September 13, 3:39 pm
Full September 20, 6:55 pm
Last September 28, 8:57 pm
Times are U.S. Central Time.
Perigee September 11
Apogee September 26
The full Moon of September is the Fruit Moon or Green Corn Moon. This year it’s also the Harvest Moon.