Fall finally arrives Thursday, Sept. 22 with the autumnal equinox. Parts of the South region were teased with a “faux fall” followed by record breaking heat, with temperatures reaching 100 degrees, during the last week of summer. But before we break out the pumpkin spice lattes and go shopping for Halloween costumes, here are five things to know about this annual astronomical event:
What is the autumnal equinox?
During the autumnal equinox, the sun shines directly on the equator, and the northern and southern hemispheres get the same amount of rays. The alignment officially occurs this year at 8:03 p.m. Thursday. Clouds notwithstanding, the South region will get about 12 hours and 15 minutes of daylight.
What does equinox mean?
But after the autumnal equinox, the northern hemisphere of the Earth begins to tilt away from the sun, so nights will get longer and days will grow shorter until the winter solstice, which will be on Dec. 21.
The Earth spins on a tilted axis as the planet orbits the sun. But twice in the course of that yearlong trip around the sun, the Earth is not inclined toward or away from the sun. Each of those instances is an equinox, which is derived from the Latin words for equal (aequus) and night (nox).
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Why is it important?
For ancient societies, the autumnal equinox marked the end of summer and the vernal (or spring) equinox marked the end of winter, which helped people track time-sensitive activity, such as when to plant crops. According to the Farmers’ Almanac, the changing colors of the leaves on deciduous trees is actually triggered by the shorter days with reduced amounts of daylight.
Forecasters’ fall started Sept. 1.
Meteorologists prefer a calendar in which the seasons start on the same days every year because it can provide consistency in record-keeping, among other reasons. But the Earth, sun and stars don’t quite conform to the Gregorian calendar — thus the autumnal and vernal equinoxes — as well as the winter and summer solstices — don’t fall on the same day every year. The autumnal equinox falls on Sept. 23 next year, but then it goes back to Sept. 22 in 2024.
What’s the difference between an equinox and a solstice?
Equinoxes – when day and night are roughly equal – occur in September and March and mark the astronomical beginning of autumn and spring in the Northern Hemisphere, respectively.
Solstices occur in December and June, which mark the beginning of astronomical winter and summer, respectively. The winter solstice occurs when the sun is at its lowest point in the sky, while the summer solstice is when the sun is at its highest point in the sky.