(WHTM) – Schools are back in session, football is back to full force on weekends, and the temperature is slowly inching its way down our thermometers — all signs that fall has arrived.

The first day of fall, or the autumnal equinox, is Wednesday — at 3:20 p.m. EST, to be precise.

But how did Sept. 22 become the official first day of fall? Why is it called fall? And why are pumpkins such a big thing this time of year?

While the first day of a season may feel like it was chosen by throwing a dart at a calendar, the actual reasoning for such a day is based on science — specifically, the positioning of the earth and the sun. This is where the term equinox comes into play. Equinox is based on the Latin word aequus, which means equal, and nox, which means night.

What occurs during an equinox?

Don’t worry, time zones aren’t magically disappearing. On the equinox, the length of day and night are about equal.

When an equinox happens, the sun is crossing the equator from one side to the other. Those of us north of the equator start experiencing fall-like weather during the autumnal equinox, while those south of the line start experiencing spring because the sun’s rays cross from the Northern Hemisphere to the Southern Hemisphere. The opposite happens on the vernal equinox, or the first day of spring.

So for one day, when the sun is right over the equator, both hemispheres enjoy roughly the same amount of daylight.

Why is it called fall?

The season, which is the only one to go by more than one commonly used name, is called “fall” because of the leaves falling from trees at this time of year. That name came about around the 1500s, according to Dictionary.com, with the name “autumn,” whose roots are obscure, dating farther back to the 1300s. Incidentally, the season also has gone by the name “harvest.”

With the sun’s warmth slowly fading away upon fall’s arrival, the climate shift also brings a shift in produce. What you see in the “locally grown” section of your market might start to take a different shape.

Pumpkins, which have been grown in North America for nearly 5,000 years, reach maturity in the fall after a long growing season, according to The Old Farmer’s Almanac. Because they need 75 to 100 frost-free days, they are typically planted by late May to early July, depending on the region, so that they are ripe before cold weather rolls in.

“Pumpkins and apples are your big fall foods,” said WHTM Chief Meteorologist and farmer Eric Finkenbinder. “People love spending an afternoon just to go and pick them. Decorating is big, too. Pumpkins, corn shocks, gourds, Indian corn. Farmer’s markets will start selling cool-season crops like broccoli, cauliflower, brussels sprouts, and cabbage.”

When do we “fall back?”

There’s one more thing to remember: Just because it’s the first day of fall, it doesn’t mean our clocks are “falling” back. That won’t happen until the end of daylight saving time on the first Sunday of November, which falls on Nov. 7 this year.