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Finally Fall! (Or Not?): Meteorological vs. Astronomical Fall

It’s starting to feel like fall! The leaves are starting to change color, the weather is getting cooler and the days are getting shorter! But wait, it’s not fall yet! It doesn’t start until September 23rd…or does it?

For all you fall lovers, ’tis the season! The first day of fall was September 1st! But, how is that possible? The calendar says fall starts on September 23rd! When you search first day of fall online, it says the same thing! Actually, both September 1st AND September 23rd mark the first day of fall, however, one is meteorological fall and one is astronomical fall! So, what’s the difference between the two?

Meteorologists and climatologists break down the year into three-month groups based on the annual temperature cycle. Fall, in this grouping, is the months of September, October and November. Each meteorological season is consistent in length and starts the same time each year. This consistency makes it much easier to calculate seasonal statistics (average fall temperature), from monthly statistics, (average monthly temperature).

Astronomical seasons are just the seasons, (winter, spring, summer, fall), that most of us all learned way back in preschool! These seasons are based on the natural rotation of Earth around the sun. This rotation results in two equinoxes, (spring, and autumnal), and two solstices, (winter and summer). The equinoxes typically fall around March 21st (Spring), and September 22nd (Autumnal), and the solstices usually fall on June 21st (Summer), and December 22nd (Winter). The equinoxes mark the times the sun is directly overhead. The variations in season length and start dates make it hard to compare seasonal statistics from one year to the next, which is why we also have meteorological seasons!

We may still have a couple weeks left until astronomical fall starts, but it’s meteorological fall and we are getting a taste of fall with the weather for a few more days! So go ahead and get out those sweaters and jackets, and grab yourself a sweet pumpkin treat because it’s fall!

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