Today marks the first day of fall for meteorologists 🍂

Did you know that there are at least two dates that mark the start of fall?

For meteorologists, the date is a little earlier than most. September 1st marks the end of summer and the start of fall.

For most everyone else, fall starts on Tuesday September 22nd in 2020.

Why the difference?

The meteorological definition has its roots in convenient record keeping. Calling the months June, July, and August “summer” has long been a meteorological standard. It’s based on the annual temperature cycle with the seasons classified by three month periods with the most similar temperatures.

Meteorological fall: September-November

Meteorological winter: December-February

Meteorological spring: March-May

Meteorological summer: June-August

Fall foliage season is not far off! 📍 Storm King Mountain, Cornwall, New York

The astronomical definition is based on the Earth’s orbit of the sun. Fall and spring begin on the equinoxes, or the days of the year when the Earth’s axis is tilted neither toward nor away from the sun. This results in a near equal amount of daylight and darkness across the world. Summer and winter begin on the solstices, when the Earth’s tilt toward the sun is at a maximum and minimum, respectively.

Each year, the date of the astronomical equinoxes and solstices are slightly different — this is because the Earth takes slightly more than 365 days to orbit the sun (365.256 days to be exact).

Astronomical fall: September 22nd, 2020

Astronomical winter: December 21st, 2020

Astronomical spring: March 20th, 2021

Astronomical summer: June 20th, 2021

In short, it would be a bookkeeping nightmare if meteorologists, in the context of record keeping, had to account for the changing dates of the astronomical seasons every year!

Clear as mud?


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