Sept. 1 marks the beginning of what is called "meteorological autumn."
However, your calendar shows that fall doesn't officially begin until Sept. 22. What's the difference?
The "official" beginnings or ends of seasons that you are accustomed to using are called "astronomical seasons." The astronomical calendar is centered around the Earth's revolution 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 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 meteorological and climatological forecasting and research. The length of the meteorological seasons is more consistent than the astronomical seasons, since 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.