Photo credit: Kristin Kizer
Meteorologically, fall began on September 1, but in the astronomical world, the first day of fall is not until September 22. The autumnal equinox occurs at 5:18 p.m. EDT on Tuesday.
To me, one of the sure signs of fall is when I notice the location of sunset has changed. The sun has been moving south each evening, from its happy, warm place in the northwest toward its chilly winter home in the southwest. On the equinox, the sun will rise directly in the east and set directly in the west.
As the sunset shifts toward the south, the time of sunset also shifts, occurring about two minutes earlier each night in September. The sun traces a shorter path across the sky as winter nears. For most people, the onrush of nightfall in autumn is a gloomy prospect, but for amateur astronomers it means more observing time with fewer late nights.
If you’re outside a couple hours after dark this weekend, look to the northeast to quickly identify four constellations. First find the W-shape of Cassiopeia, which is the most recognizable. To its right is a giant box shape, known as the Great Square of Pegasus. Below Cassiopeia, hanging like an icicle toward the horizon, are the stars of Perseus.
For the final constellation, look between Perseus and the Great Square of Pegasus to find Andromeda. The constellation Andromeda is not very distinctive, but it is home to the easiest galaxy for amateur astronomers to spot. The Andromeda Galaxy is bright enough to be visible through binoculars or even with the naked eye in a truly dark location. When you see it, it’s incredible to think that the light that is just now reaching your eyes left its source 2.9 million years ago. Observing the universe opens a window for us to see back in time.
Put in perspective, those long sunny days of summer don’t seem quite so long ago anymore.
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Kelly Kizer Whitt loves clean, clear, and dark skies. Kelly studied English and Astronomy at the University of Wisconsin-Madison and worked for Astronomy magazine. She is currently the Feature Writer for Astronomy and Space at Suite101.com. You can follow her on Twitter at twitter.com/Astronomommy.