Despite the fact that the pumpkin spice latte debuted this year in August, fall actually doesn’t begin until Saturday, Sept. 22, 2018. This day not only marks the unofficial start of sweater weather, it it also has a scientific significance: the autumnal equinox.
The equinox isn’t just a day, it’s a minute.
According to The Weather Channel, the autumnal equinox happens at 9:54 p.m. EDT, marking the official end of summer and the beginning of fall. During that minute, the sun crosses the Earth’s equator from the Northern Hemisphere into the Southern Hemisphere and day and night last the exact same amount of time — 12 hours — everywhere across the world.
So why does this happen? Throughout the year, the earth tilts on its axis at a diagonal away from or toward the sun, causing the change in seasons. During the equinox, it becomes momentarily perfectly perpendicular, meaning the sun’s rays pass directly over the equator. Following that minute, the Northern hemisphere begins to tilt away from the sun leading to shorter days and cooler temperatures. It also causes a shift in the jet stream, which affects weather patterns.
Equinoxes happen twice a year, once in the spring and once in the fall, while the solstices occur once in the summer and once in the winter. During an equinox, the sun is at the closest distance to the equator, while during a solstice it is the furthest distance away.
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What time does your the autumnal equinox begin in your time zone?
Eastern Daylight Time: 9:54 p.m.
Central Daylight Time: 8:54 p.m.
Mountain Daylight Time: 7:54 p.m.
Mountain Standard Time (Arizona): 6:54 p.m.
Pacific Daylight Time: 6:54 p.m.
Alaska Daylight Time: 5:54 p.m.
Hawaii-Aleutian Standard Time: 3:54 p.m.