At 8:07pm Eastern Daylight Saving Time, 20 March 2007, Spring began. This date and time mark the vernal equinox- equal hours of daylight and darkness that occur twice a year in spring and fall.
For more information on this in Ball State's University Libraries and online:
Do keyword searches in CardCat for "vernal," "spring," "autumnal," or "fall" "equinox," or "soltices." You can also type in terms such as "astronomy" or "seasons" for more general information.
You can also find books on this subject and astronomy in general on the shelves under call numbers beginning with Q14 (encyclopedia, dictionaries, glossaries, etc.) or QB63-65 (field guides, star charts, manuals, etc.).
"The Egg and the Equinox" from Phil Plait's Bad Astronomy
"The Equinox" from Wolfram Research
SkyTonight Almanac from Sky & Telescope
Earth's Seasons: Equinoxes, Solstices, Perihelion, and Aphelion from the US Naval Observatory