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Say your goodbyes to warm weather and hello to sweater season. Fall arrives Thursday.
The autumn equinox, when the sun's center crosses the equator, will happen tonight at 9:04 pm EST, marking the beginning of fall in the Northern Hemisphere. Those living south of the equator will transition from winter to spring.
The first day of fall and spring are defined as equinoxes, while the start of summer and winter are labeled solstices. They both occur twice a year but have some major differences.
First, according to the National Weather Service, when the Earth's axis is not titled toward, or away, from the sun, it allows for an equal amount of daylight and darkness, known as an equinox.
"At the equator, the sun is directly overhead at noon on these two equinoxes," the NWS says on its website. "The 'nearly' equal hours of day and night are due to refraction of sunlight or a bending of the light's rays that causes the sun to appear above the horizon when the actual position of the sun is below the horizon."
Because the sun takes more time to rise and set, the days will become a little longer in areas with higher latitudes. The length of a day following an equinox will typically be 12 hours and seven minutes near the equator.
But areas with 30 degrees latitude will have days that last 12 hours and 8 minutes, while 60-degree latitude results in 12 hours and 16 minutes.
During the autumn equinox, the Northern Hemisphere experiences the fastest loss of daylight, with places like Washington, D.C., expected to lose two minutes, 30 seconds of daylight per day. Miami will lose 90 seconds.
However, as a result of a solstice, the Earth tilts up to 23.5 degrees, both near and away from the sun. When the summer solstice occurs, the sun reaches its highest elevation over the Tropic of Cancer in the Northern Hemisphere, affecting countries like Mexico, the Bahamas, Egypt, Saudi Arabia, India and southern China.