The vernal equinox 2009 happens tomorrow, March 20, bringing in the official start of spring. The spring equinox happens at 7:44 a.m. EDT.
Vernal Equinox 2009: What Is It?
The vernal equinox occurs when the sun passes directly over the equator, diving night and day into equal lengths. It is one of two equinox events during the year: The autumnal equinox, or fall equinox, happens in September and marks the start of the fall season for the northern hemisphere.
Live Science has a great write-up about the science behind the equinox here.
First Day of Spring 2009
The first day of spring 2009, then, is the same day as the equinox: this Friday, March 20. Plenty of cities are marking the occasion with celebrations either Friday or over the weekend. Check your local media outlets to find the specifics for your area.