09/01/2026
How do you measure the seasons?
Meteorologists and climatologists break the seasons down into clearly defined groupings of three months based on the annual temperature cycle and the Gregorian calendar.
For these record keepers in the Northern Hemisphere, fall begins on September 1st and ends on November 30th each year.
Marking the seasons in this way allows these scientists to easily compare weather patterns and climate data from year to year.
In contrast, astronomers and orbital scientists use astronomical seasons, which are based on the position of Earth in relation to the sun.
Astronomical fall is precisely tied to an astronomical event. This makes it undebatably accurate, but variable. It starts on the autumnal equinox, which occurs between Sept. 21 and Sept. 23, and ends on the winter solstice, which occurs between Dec. 20 and Dec. 22. These dates vary due to leap years and the elliptical shape of Earth's orbit around the Sun.
The autumnal equinox marks one of two days each year when the Earth's axis does not tilt toward or away from the sun. This year, on Tuesday, September 22nd at 8:05 p.m. EDT, the sun will shine directly above the Earth's equator.
The word equinox is derived from the Latin words aequus (equal) and nox (night). On September 22nd, 2026, day and night will be approximately equal in length everywhere on Earth.
So, we can welcome fall's arrival twice each year!
Happy meteorological fall!
