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PHILADELPHIA (CBS Local) — The season of pumpkin beverages and fall colors is officially almost here.

The Fall equinox occurs this Saturday, Sept. 22, at precisely 9:54 p.m. ET and here’s what you need to know.

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Also known as the Autumnal equinox and the September equinox, the Fall equinox is technically not a day-long event, even though many choose to celebrate all day. It occurs at the moment the Sun crosses the celestial equator, the imaginary line in the sky above Earth’s equator.

The Fall equinox usually occurs on Sept. 22 or 23, but it can fall as early as Sept. 21 or as late as Sept. 24 on rare occasions. The equinox dates vary because of the difference between the Gregorian calendar, which defines a year as 365 days, and the time it actually takes for Earth to complete its orbit around the sun (about 365 and 1/4 days).

Equinox is derived from Latin, meaning “equal night,” so most places on Earth will see approximately 12 hours of daylight and 12 hours of night. The Northern Hemisphere will start seeing shorter days and longer nights and the Southern Hemisphere will see a reversal in seasons — all due to the Earth’s tilt.

Daylight in the Northern Hemisphere hours will continue to shorten until the winter solstice on Dec. 21.

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It is less light, more than a change in temperature, that signals leaves on deciduous (green leafy) trees to stop producing chlorophyll, offering up spectacular colors for fall foliage. Temperature and weather conditions, however, can impact the intensity of fall colors and how long they linger.

Despite the change in season, Daylight Saving Time continues through Sunday, Nov. 4, so you have a few more weeks before you need to change your clocks.