Summer At Last!!!
What better source than The Old Farmers' Almanac:
Summer begins in the Northern Hemisphere on June 20, 2012, at 7:09 P.M. (EDT)...
The Summer Solstice
Each year, the timing of the solstice depends on when the Sun reaches its farthest point north of the equator. This occurs annually on June 20 or June 21 in North America, depending on your time zone.
The word solstice is from the Latin solstitium, from sol (sun) and stitium (to stop), reflecting the fact that the Sun appears to stop at this time (and again at the winter solstice).