The summer solstice occurs when the sun is the farthest north in the sky, directly above the Tropic of Cancer. According to USA Today, the exact moment of the solstice today will occur at 1:16 p.m. ET.
While some consider the summer solstice as the beginning of summer, many actually regard it as midsummer, though the definition varies between different regions and cultures. In the Southern Hemisphere, today actually marks the 2011 winter solstice. These seasons will again be flipped between the hemispheres on December 22, when the second solstice of the year occurs (winter for Northern Hemisphere, and summer for Southern Hemisphere).
On June 21, there are 24 hours of daylight north of the Arctic Circle (66.5° north of the equator) and 24 hours of darkness south of the Antarctic Circle (66.5° south of the equator). The sun's rays are directly overhead along the Tropic of Cancer (the latitude line at 23.5° north, passing through Mexico, Saharan Africa, and India) on June 21.
Although it's the longest day of the year, it usually isn't the warmest, International Business Times reports.
The Sun's angle is high before and after the summer solstice with a maximum number of daylight minutes. As the Sun begins to move lower in the sky, the length of daylight decreases, National Weather Service says.
For example, in New Mexico's Albuquerque, the maximum daily temperature occurs nearly 3 weeks later in mid July. This lag in temperature occurs because even though the minutes of daylight are decreasing, Earth's surface and atmosphere continues to receive more energy than just what it receives from the Sun. Average temperatures continue to climb until the Sun drops lower in the sky.
Many different people around the world celebrate the solstices, including a large gathering that happens every year at Stonehenge. This year, around 18,000 people were present at Stonehenge to witness the sunrise on the summer solstice, AP reports.
Even Google is celebrating the summer solstice with today's Google Doodle. According to Mashable.com, Japanese artist Takashi Murakami created the colorful logo, likewise making a winter version for those south of the equator.
Do you celebrate the summer solstice? Let us know your plans for the longest day of the year in the comments.