Tuesday, September 1st marks the beginning of what is called "meteorological autumn".
However, fall doesn't officially begin until September 22nd. What's the difference?
The "official" beginnings or ends of seasons of which you are accustomed to hearing are called "astronomical seasons". The astronomical calendar is centered around the earth's rotation around the sun.
The earth's orbit around the sun, combined with our home planet's tilt, gives us our seasons.
The astronomical beginning of spring occurs when the sun is directly over the equator and is called the Vernal Equinox, which occurs in late March.
Summer officially begins with the Summer Solstice, which is when the sun is directly over the Tropic of Cancer.
The Autumnal Equinox marks the beginning of autumn, and that is when the sun is directly over the equator once again.
Finally, the Winter Solstice, when the sun is directly over the Tropic of Capricorn, marks the beginning of winter.
So what about the meteorological seasons that I mentioned earlier?
- Meteorological spring is March, April, and May.
- Meteorological summer is June, July, and August.
- Meteorological fall is September, October, and November.
- Meteorological winter is December, January, and February.
These meteorological seasons were created for the purposes of meteorological and climatological forecasting and research. The length of the meteorological seasons is more consistent than the astronomical seasons (the dates of the equinoxes and solstices can vary by a few days each year).
Meteorological seasons also more closely follow our regular calendar. For these two reasons, this makes the use of the meteorological seasons easier for study and research, including calculating seasonal averages for temperatures, precipitation, and more.