From Live Science:
The first day of autumn — Sept. 22 this year — is no guarantee of fall-like weather, but officially the season's start comes around at the same time each year nonetheless.
Well, sort of.
The first day of autumn arrives on varying dates in different years for two reasons: Our year is not exactly an even number of days; and Earth's slightly noncircular orbit, plus the gravitational tug of the other planets, constantly changes our planet's orientation to the sun from year to year.
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