Today, June 20, is the summer solstice in the Northern Hemisphere, which means that today is the longest day of 2012. It also is the first official day of summer.
According to Almanac.com, the sun reaches its most northern point in the sky at local noon on the summer solstice, which creates more sunlight in the Northern Hemisphere on this day than any other. But it's all downhill from here: after this date, days start getting shorter and the sun gets progressively lower in the sky until mid December.
The summer solstice falls today at 7:08 p.m. EDT.
The timing of the solstice each year depends on when the sun reaches its farthest point north of the equator.
Alamanac.com points out that 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.
While today is the summer solstice in the Northern Hemisphere, residents in the Southern Hemisphere (if they're in spots that are cold enough) will be wrapping up in their warm clothes in honor of the winter solstice, which is the shortest day of the year and official start of winter, according to almanac.com.