Summer Solstice 2011

June 21, 2011 (17:16 UTC) ushers in the summer solstice; summer will officially start at 1:16 pm EDT today. What exactly is this summer solstice? 

The summer solstice (also called the vernal equinox), and is derived from the Latin 'sol' (sun) + 'stitium' (standing), meaning 'sun to stand still.' This is a major celestial event, for today will be the longest day and shortest night of the whole year; the exact opposite is the winter solstice. Now mind you, this is the longest day for the Northern Hemisphere. The Southern Hemisphere will experience their 'summer solstice' in December; May - September are usually the 'winter months.' Wikipedia writes,

Of the many ways in which solstice can be defined, one of the most common (and perhaps most easily understood) is by the astronomical phenomenon for which it is named, which is readily observable by anyone on Earth: a "sun-standing."

This diagram from NASA will help you understand this better: 

Seasons of 2011:
SPRING EQUINOX	March 20, 7:21 P.M. EDT
SUMMER SOLSTICE	June 21, 1:16 P.M. EDT
FALL EQUINOX	September 23, 5:05 A.M. EDT
WINTER SOLSTICE	December 22, 12:30 A.M. EST

Earth Sky finishes, proclaiming:

Because Earth doesn’t orbit upright, but is instead tilted on its axis by 23-and-a-half degrees, Earth’s northern and southern hemispheres trade places in receiving the sun’s light and warmth most directly.

At the June solstice, Earth is positioned in its orbit so that the North Pole is leaning 23 1/2 degrees toward the sun. As seen from Earth, the sun is directly overhead at noon 23 1/2 degrees north of the equator, at an imaginary line encircling the globe known as the Tropic of Cancer – named after the constellation Cancer the Crab. This is as far north as the sun ever gets.