Overview
- The equinox occurs tonight, Tuesday Sept. 22, at 8:05 p.m. Eastern Time, the exact instant the Sun’s center crosses Earth’s equator and the Northern Hemisphere moves into astronomical autumn.
- NOAA estimates that many U.S. states will lose about 3 to 3.5 hours of daylight between the equinox and the winter solstice on Dec. 21, meaning earlier sunsets and longer nights over the coming months.
- The observed roughly 12‑hour day known as the equilux often falls on different dates from the equinox because the Sun is a disk and the atmosphere refracts light, so places like Maine see an equilux around Sept. 25 while Raleigh’s falls near Sept. 27.
- The Harvest Moon — the full moon nearest the equinox — reaches full illumination around Sept. 26, producing quicker moonrises after sunset for several evenings and prompting local harvest and equinox events.
- Time zones change the local clock moment of the same equinox instant, seasonal timing combines with meteorological fall (which began Sept. 1), and factors such as El Niño and daylight‑saving clocks will shape regional weather, foliage timing and daily life.