Autumnal Equinox


Oh it’s a long, long time

From May to December
But the days grow short

When you reach September

    September Song

Many of you no doubt recognized that opening verse from September Song.  Many singers have recorded it, but perhaps you are particularly fond of Willie Nelson’s rendition, or that of Frank Sinatra.

And indeed, the days are getting shorter.  Summer is now officially in the rearview mirror.  Our day lengths change throughout the year, of course.  That is because the earth does not rotate perpendicular to the direction of its orbit.  The earth’s angle of rotation is tilted by 23.5 degrees, so the directness of sunlight hitting the earth changes throughout the year, which causes the change of season.  And for those of us living in the higher latitudes, the changes are great.

The autumnal equinox occurred Friday (22nd) at 3:02 pm Central Daylight Time when the sun was directly over the equator.  The days have been getting shorter and the sun has been arcing further southward in the sky since the summer solstice back in June.  Those changes will continue until the winter solstice in December.

Sunrise and sunset in Bismarck on the Autumnal Equinox was 7:30am and 7:40pm Central Daylight Time.  That is 12 hours and ten minutes between sunrise and sunset.  On the Summer Solstice back on June 21 sunrise and sunset were 5:49am and 9:41pm.  That was a whopping 15 hours and 52 minutes between sunrise and sunset.

So we already have lost 3 hours and 42 minutes of sunlight since the summer solstice.  And we are going to lose more.  When the Winter Solstice occurs on December 21, sunrise and sunset will be at 8:25am and 4:58pm in Bismarck.  That is only 8 hours and 33 minutes of daylight.  Many of us will be going to work and coming home in the dark.

But the good news is that after the Winter Solstice the days will lengthen, and the sun will slowly arc back northward.  We will gain a minute or two of sunlight each day, so that by the time of the Spring Equinox we will be back around 12 hours of daylight again.  And before we know it, we will be soaking up those 15 hour days of summer sun again.

Chuck Lura

Natural North Dakota is supported by NDSU Central Grasslands Research Extension Center and Dakota College at Bottineau, and by the members of Prairie Public. Thanks to Sunny 101.9 in Bottineau for their recording services.

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