The first date of spring, also known as the spring equinox or vernal equinox, varies slightly depending on the year and time zone. In the Northern Hemisphere, the spring equinox typically occurs around March 20th or 21st, while in the Southern Hemisphere, it typically occurs around September 22nd or 23rd. The spring equinox marks the moment when the sun crosses the celestial equator, and day and night are approximately equal in length.