In 2023, the official first day of spring is Monday, March 20 at 5:24 P.M. EDT. This date marks the “spring equinox” in the Northern Hemisphere and is the astronomical beginning of the spring season and the autumn season in the Southern Hemisphere. If you thought that the spring equinox only ever occurred on March 21, you may be dating yourself. Astronomically speaking, the first day of spring is marked by the spring equinox, which falls on March 19, 20, or 21 every year. Interestingly, due to time zone differences, there isn’t a March 21 equinox in mainland U.S. during the entire 21st century! We won’t see a March 21 equinox again until 2101. Equinoxes are the only two times each year that the Sun rises due east and sets due west for all of us on Earth! On the equinox, the length of day and night is nearly equal in all parts of the world. The equinox happens at the same moment worldwide, although our clock times reflect a different time zone.