The vernal equinox.

Space.com

The vernal equinox, which occurred today at 7:02 a.m. EDT (March 20), is popularly described as "the first day of spring" in the Northern Hemisphere, but is actually much more important than that as it marks the beginning of the astronomical year.

Vernal Equinox Marks First Day of Spring Today

oak.ctx.ly

Here's exactly what's happening to Planet Earth.