The 2023 Fall Equinox is upon us. Saturday, Sept. 23 will mark the official end of astronomical summer and start of the astronomical fall season.
Earth's axis doesn't point straight up and down relative to the plane of its orbit. This means that most of the time, the planet is tilted so that part of it receives more sunshine than the other.
In each hemisphere, summer months occur when that part of the planet is tilted closer to the sun, and vice versa in winter.
But twice a year — once at the end of winter and once at the end of summer — the planet is tilted in just the right way to ensure that both the northern and southern hemispheres get a nearly equal amount of sunlight.
Every year, the spring equinox lands somewhere between March 19 and 21. The Fall equinox occurs somewhere between Sept. 21 and 24.
These astronomical events mark a certain point in Earth's orbit, and may not match the weather we typically associate with a season. Weather, which is driven by many variables including temperatures, pressures, and other climatological conditions, can vary a lot in a single day across a country the size of the U.S.
This weekend, for example, temperatures are forecast to reach the 70s across much of the country, with pockets of triple-digit highs in south Texas, with temperatures at or below freezing in Yellowstone within the same 24 hours.
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