2016: Sidereal Signs of Autumn


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The autumnal equinox occurs on September 22, 2016 at 9:21 a.m. CDT.  At this moment the sun’s rays are most direct at the equator.  Astronomically, the sun’s coordinates are at 12 hours of right ascension and 0 degrees of declination.  If you not into the technicalities of this event, there’s another way to note that autumn has arrived.  One way is to look toward the western horizon early in the evening.  Near the time of the start of autumn, the Big Dipper lies low in the northwest.  Perhaps trees or your neighbor’s house blocks its view.  Locate a clear horizon to see these stars.

 In North America, the Big Dipper is one of the first star patterns that children learn when they visit their local planetarium.  Its familiar seven stars are part of the formal group call Ursa Major, the Great Bear.  The handle of the dipper points toward Arcturus, a distinctly red-orange star in the western sky.  Follow the bend of the Big Dipper’s handle toward the star Arcturus, or as the familiar saying goes, “Follow the arc to Arcturus.”  Arcturus is part of a large constellation known as Bootes, the Herdsman, that resembles a kite.

As a large celestial calendar, the stars indicate the seasons as well as the sun’s location on the great sidereal sphere.  As the earth revolves around the sun, we see a distinct layout of stars in the night sky each season.  The Big Dipper and Arcturus in the western sky make a sidereal sign that autumn has arrived.

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