The summer solstice occurred today at 1:16 p.m. EDT (17:16 GMT), the time the sun is at the highest point possible in the sky. In the Northern Hemphisphere, June 21 is the longest day of the year and marks the official beginning of summer.
Today, the North Pole is tilted toward the sun more than any other day in 2011. The summer solstice is a result of the Earth tilted on its axis 23.4 degrees in the direction of the sun, exposing most of the Northern Hemisphere to sunlight.
Solstice is derived from Latin words meaning, "sun stands still." The summer solstice occurs when the sun is directly overhead at noon at the Tropic of Cancer.
For the Southern Hemisphere, everything is opposite. Today is the actually the beginning of the winter solstice and the shortest day of the year for the Southern Hemisphere.
Wherever a person is on the earth today, solstices occurred at the exact moment across all global timezones
Even though on June 21 is the day that the Northern Hemisphere receives the most sunlight in 2011, it is not necessarily the hottest day of the year. Since it takes several weeks for the earth to release the heat from the sunlight, the hottest days in summer are usually in July or August.
The date of the solstice can vary from year to year. The summer solstice usually occurs between June 20 and June 21 in the Northern Hemisphere and between December 20 and December 21 and December 21 in the Southern Hemisphere.
The shifts in the date for the solstice are a result of the discrepancy between the 365-day human calendar year and the 365.24-day astronomical year.
In 2012, the solstice will be on June 20 at 23:09 GMT.