Did you know that there are two dates that mark the start of spring?
For meteorologists, the date is a little earlier than most. March 1st marks the end of winter and the start of spring.
For most everyone else, spring starts on Saturday March 20th.
Why the difference?
The meteorological definition has its roots in convenient record keeping. Calling the months March, April, and May “spring” 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 spring: March-May
Meteorological summer: June-August
Meteorological fall: September-November
Meteorological winter: December-February
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 spring: March 20th, 2021
Astronomical summer: June 20th, 2021
Astronomical fall: September 22nd, 2021
Astronomical winter: December 21st, 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.
Whether you prefer the meteorological or astronomical definition, happy spring! 🌳