sol" (sun) and " stitium" (still or stopped). It is used to describe the exact moment when the poles are tilted at their maximum toward or away from the sun. The summer solstice occurs when the sun is directly above the Tropic of Cancer, which is the circle marking the latitude 23.5 degrees north, and which runs through Mexico, the Bahamas, Egypt, Saudi Arabia, India and southern China, according to the National Weather Service. For those living above the Tropic of Cancer, it is the longest day of the year. For those who live in the Southern Hemisphere, this is the shortest day of the year and marks the arrival of winter. The longest day of the year for those south of the equator occurs between Dec. 20 and 22, when the sun is directly above the Tropic of Capricorn. This marks the winter solstice where the Northern Hemisphere will experience the shortest day of the year.