The spring equinox is here. What does that mean?

The sun sets behind the Olympic Mountains as people cross a street in Seattle's Alki neighborhood on the last evening of winter on Monday, March 18, 2024. Seattle saw unseasonably warm temperatures as winter turned into spring. The vernal equinox arrives on Tuesday, March 19, marking the start of the spring season for the Northern Hemisphere. (AP Photo/Manuel Valdes)