A traffic jam highlights the morning sky this month, as three planets line up near Regulus, the heart of Leo. The planets move through different configurations during the month, providing a different view each day. In the evening sky, some of the signature constellations of summer begin dropping from view, while some of the faint constellations of autumn climb skyward in the east and southeast.
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In the Sky This Month
September 20: Pegasus
With summer about to give way to fall, one of the main star patterns of the new season is climbing into prominence in the evening. The Great Square of Pegasus is in the east at nightfall. It’s tilted as it rises, so it looks like a diamond.
September 21: Moon and Jupiter
The giant planet Jupiter is close to the left of the crescent Moon shortly after sunset tonight. Although it is quite low in the sky, if you have a clear horizon you should be able to spot it through the fading twilight.
September 22: Autumn
Autumn arrives in the northern hemisphere at 3:02 p.m. CDT, the moment of the autumnal equinox. The season changes when the Sun crosses the equator from north to south. The Sun will continue its southward trek until the winter solstice, in December.
September 23: Cetus
The constellation Cetus, the whale or sea monster, is swinging into view in the evening sky. It is low on the eastern horizon around 10 or 11 p.m., and never climbs very high during the night.
September 24: Scutum
Scutum, a small, faint “shield” of stars, scoots across the southwestern sky on early autumn nights. It represents the coat of arms on the shield of John Sobieski, a 17th-century king of Poland and one of that country’s great heroes.
September 25: Moon and Companions
Antares, the bright heart of the scorpion, stands below the Moon as night falls, shining bright orange. The brighter planet Saturn is about the same distance to the left of the Moon.
September 26: Moon and Saturn
A pair of bright objects stands in the southwest this evening: the Moon and the planet Saturn. Saturn, the solar system’s second-largest planet, perches below the Moon, and looks like a bright star.