Seasons

The rule of thumb that autumn begins on Sept. 20 or 21 is just that: something easy to remember but not necessarily accurate.

The same goes with the old idea that on the first day of fall, day and night are the same length. Not necessarily so.

The U.S. Naval Observatory offers a great Web site to learn about the motion of the sun and the moon across the sky. Here is a quote from its page on the change of seasons:

“Day and night are not exactly of equal length at the time of the March and September equinoxes. The dates on which day and night are each 12 hours occur a few days before and after the equinoxes. The specific dates of this occurrence are different for different latitudes.

“… At higher latitudes in the northern hemisphere, the date of equal day and night occurs before the March equinox. Daytime continues to be longer than nighttime until after the September equinox.”

The equinox occurred at 12:03 a.m. today, making this the first day of autumn. The first day of fall is either Sept. 22 or Sept. 23 through the year 2020.

The closest we come to 12 hours between sunrise and sunset is Sept. 26, if I read the table for Huntington correctly.