Autumn Equinox: Exploring When Fall Begins

On September 22, the autumnal equinox marks the beginning of fall in the Northern Hemisphere at 2:19 p.m. EDT. This annual event occurs when the sun is directly above the equator, causing the Earth to have no tilt with respect to the sun.

The National Oceanic and Atmospheric Association explains that Earth's tilt aligns with its cycle around the sun twice a year, in March and September. Meanwhile, in the Southern Hemisphere, the vernal equinox on September 22 signals the start of spring.

During the equinox, day and night are approximately 12 hours long worldwide, giving rise to the term "equinox," derived from the Latin words for "equal night."

The Earth's axis is not tilted toward or away from the sun during the autumnal equinox, resulting in nearly equal amounts of daylight and darkness at all latitudes, as noted by the National Weather Service.

The Earth's 23.5-degree tilt causes seasonal changes as it orbits the sun, with the sun rising almost due east and setting nearly due west on September 22 for most of the world.

While some consider the autumnal equinox as the official start of fall, there is no formal designation by any administrative or political organization. Astronomers mark the end of summer on September 22, but meteorologists and climatologists consider August 31 as the end of summer in the Northern Hemisphere.

Equinoxes in September and March signal the start of autumn and spring in the Northern Hemisphere, respectively, while solstices in December and June mark the beginning of winter and summer, respectively.

As the Earth's tilt exposes the Northern Hemisphere to the sun's rays less directly, days will become darker and shorter as winter approaches.