Although the autumnal equinox is observed, maybe even celebrated, all day on Sept. 23, it's really just a moment in time — to be exact it's when the sun crosses the celestial equator, an imaginary line in the sky above Earth's equator.
Normally, Earth orbits tilted on its axis by 23.5 degrees. But at this precise instant, its rotational axis is neither tilting toward nor away from the sun.
For 2023, that takes place at 2:50 a.m. EDT. After this time, the sun will start rising later and setting earlier for those in the Northern Hemisphere.
Those living in the Southern Hemisphere will see the opposite. In fact, people in the Southern Hemisphere refer to Sept. 23 as the spring equinox, a signal that the days will start getting longer.