The Equinox http://en.wikipedia.org/wiki/Vernal_equinox http://www.clarkfoundation.org/astro-utah/vondel/equinoxver.html http://solar.physics.montana.edu/YPOP/Classroom/Lessons/Sundials/equinox.html http://www.equinox-and-solstice.com/html/vernal_equinox.html