You may not have seen your first red leaf fall on the ground just yet, but that doesn't mean summer is lasting much longer this year compared to years past  at least, according to the calendar. Though the weather has been giving off more beach than bonfire vibes, the first day of fall is really just around the corner.Sept. 22 at 8:43 a.m. Eastern Time will mark the official start of the fall season, as that's the time of this year's autumnal equinox in the Northern Hemisphere (even if it may seem like the return of pumpkin spice lattes at Starbucks, which happened last month, is the true tell of when fall begins).In both the spring and the fall, an equinox is the astronomical event that marks the official changing of the seasons, while a solstice marks the beginning of winter and summer. An equinox occurs when the Earth's axis is tilted to a relative point where the sun shines directly on the center of the planet's equator, creating an equal balance of day and night to around 12 hours globally.RELATED STORY | The history behind pumpkin spiceThe autumnal equinox mainly falls on Sept. 22 or 23 each year, though rarely it can fall on the 21 or 24. The first day of fall last year was Sept. 23, but it won't be again until 2027, according to the Farmer's Almanac. In the Southern Hemisphere, the autumnal equinox typically happens every March 19 or 20, meaning everything is reversed, so happy almost spring to them!Back in the Northern Hemisphere, from the autumnal equinox until the winter solstice, the daylight hours will start to shorten as nights lengthen. Temperatures start dropping and plant life starts slowing  and maybe humans slowing, too. That's until the winter solstice, which will be Dec. 21 this year in the Northern Hemisphere. Then on Nov. 3, we say goodbye to daylight saving time once again, which we've been in since March 10 to enjoy longer hours of daylight during the warmer months. The changing of the clocks falls back in autumn, so we'll be gaining an hour. So grab your sweaters and turn on the TV, it's football  I mean  fall season again!RELATED STORY | Retailers pushing a 'Fall Creep' on autumn products