While the fall equinox marks the official start of the astronomical autumn season, it is not the day where we receive exactly 12 hours of daylight and 12 hours of darkness. That distinction belongs to what's known as the equilux, which means "equal light".
The equilux is the day when sunrise and sunset are separated by almost exactly 12 hours, resulting in an equal balance of day and night. Because of the Sun's size and the way Earth's atmosphere bends sunlight, the equinox and equilux do not occur on the same day. For instance, Rockford's spring equilux took place on March 17th, while the autumn equilux is scheduled to occur tomorrow, September 26th. Our sunrise is at 6:47AM and sunset is at 6:48PM, giving that equal split in day and night. Once the equilux passes, daylight hours continue to shrink, allowing nights to grow longer.
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