What Is the <br />Autumnal Equinox? The autumnal equinox, also known as the<br />September equinox, occurs the moment<br />the sun crosses the celestial equator. During the day this occurs, the length of night<br />and day are nearly equal, as the sun is shining<br />directly perpendicular to the equator. It is for that reason we call it an “equinox,” which<br />is derived from the Latin word for “equal night.” The September equinox occurs on either the<br />22, 23 or 24 of the month, with this year’s equinox<br />occurring on Sept. 23 at around 3:50am EST. For the Northern Hemisphere, this signals<br />the first day of fall, while in the Southern<br />Hemisphere, it signals the first day of spring. Earth’s axis is typically tilted at a 23.4 degree<br />angle, which means either the southern or northern hemisphere is more tilted <br />towards the sun. During that time period and until the equinox,<br />that hemisphere receives more sun than the other,<br />causing the varying seasons of winter and summer.
