Photo: Laura Durenberger-Grunow

By Laura Durenberger-Grunow - Boreal Community Media - September 22, 2025

Today, September 22, 2025, at 1:19 p.m. central time, marks the official start of fall in the northern hemisphere, with the arrival of the autumnal equinox. Derived from the Latin words aequus (equal) and nox (night), it is a moment when the sun shines directly on the Earth's equator. The result is an approximate 12 hours of daylight and night at all latitudes (and yes, after today, the days start getting shorter for us in the northern hemisphere). 

According to NASA, the equinox "marks the exact moment when the center of the Sun crosses the plane of our planet's equator." At this point, the tilt of the planet's axis (which typically orbits the sun tilted at approximately 23.5 degrees) is neither toward nor away from the Sun. For those at the equator, the Sun appears directly overhead at solar noon.

While the term "equinox" suggests a perfect 12-hour split, the National Weather Service states that due to factors like the refraction of sunlight by the atmosphere, the day is slightly longer than the night. This bending of light allows us to see the Sun before it has truly risen and after it has set. Because of this, the days of truly equal daylight and darkness, known as the equilux, typically occur a few days after the autumnal equinox, and a few days before the spring equinox.

 Image: NASA