When the Autumn Equinox Arrives?

Saturday, September 22, 2018 - 15:45

The 2018 autumn equinox, which officially marks the start of fall, arrives on Saturday night, Sept. 22, in the Northern Hemisphere.

Sept. 22 is the first day of fall because it is when the autumnal equinox — the moment when “a planet’s subsolar point passes through its equator,” according to National Geographic — takes place.

The same astronomical setup occurs each spring, with the sun moving straight over the equator. In late March, this occurrence is known as the vernal equinox or the spring equinox and it marks the official start of the spring season — with longer days and warmer weather.

Weather folks break the year up into four "meteorological seasons," each of which lasts for three full months and begins on the very first day of the month: Sept. 1 for autumn; Dec. 1 for winter; March 1 for spring, and June 1 for summer.

The most notable and immediate change with the equinox is that the day and night have equal length, according to the National Oceanic and Atmospheric Association (NOAA). The word “equinox” means “equal night” in Latin.


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