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Fall officially begins this weekend, although parts of the U.S. have already seen signs of the cooler temperatures this season brings this month.
Here are five things you should know about the autumn equinox:
1. The start of fall on Sunday, September 22nd depends on where you live: If you are in the Eastern Time Zone, fall officially begins at 8:43 a.m. local time. In the Central Time Zone, fall begins at 7:43 a.m., in the Mountain Time Zone, it begins at 6:43 a.m., and in the Pacific Time Zone, it begins at 5:43 a.m.
(MORE: Fall foliage tracker)
2. For this reason, there is a time, accurate to the minute, that marks the beginning of autumn: Twice a year, around March 20 or 21 and September 22 or 23, the sun’s rays shine directly over the equator. In the Northern Hemisphere, these times are called the spring equinox and the autumn equinox.
The exact moment, this year 8:43 a.m. EDT, marks the transition of direct sunlight across the equator from the Northern to the Southern Hemisphere.
3. Day and night are in balance at the equinox, but daylight is now decreasing: Instead of being tilted away from or toward the Sun, during the equinoxes the Earth’s axis of rotation is perpendicular to the line connecting the centers of the Earth and the Sun.
Because of this, day and night are balanced at almost 12 hours each around the world. You can see this in the satellite image of the equinox on September 23, 2019, which is half sunlit and half nocturnal (dark areas).
From this point on, the days in the Northern Hemisphere will gradually become shorter until the winter solstice on December 21, 2024. The reason for this is because the Earth in the Northern Hemisphere is tilting away from the Sun.
This GOES East image was taken on September 23, 2019 at 8:00 a.m. EDT
(NOAA)
4. In the southern hemisphere everything is reversed: South of the equator, the equinox in September marks the beginning of spring.
In countries like Australia and South America, the days get longer until summer begins in December because the sun’s rays are most direct in these parts of the world.
5. Fall and Autumn are used synonymously, but there is a difference in meaningFor more information, please see our full statement here.
Chris Dolce has been a senior meteorologist at weather.com for more than 10 years after beginning his career at the Weather Channel in the early 2000s.
