1:35 PM EST Today: The Reason For The Season

The precise moment of the 2005 solstice will be December 21, 2005 at 1:35 P.M. EST (18:35 UT).

In the Northern Hemisphere, the winter solstice occurs either December 21 or 22, when the sun shines directly over the tropic of Capricorn; the summer solstice occurs either June 21 or 22, when the sun shines directly over the tropic of Cancer. In the Southern Hemisphere, the winter and summer solstices are reversed.

Reason for the Seasons

The reason for the different seasons at opposite times of the year in the two hemispheres is that while the earth rotates about the sun, it also spins on its axis, which is tilted some 23.5 degrees towards the plane of its rotation. Because of this tilt, the Northern Hemisphere receives less direct sunlight (creating winter) while the Southern Hemisphere receives more direct sunlight (creating summer). As the Earth continues its orbit the hemisphere that is angled closest to the sun changes and the seasons are reversed.

Longest Night of the Year

The winter solstice marks the shortest day and the longest night of the year. The sun appears at its lowest point in the sky, and its noontime elevation appears to be the same for several days before and after the solstice. Hence the origin of the word solstice, which comes from Latin solstitium, from sol, "sun" and -stitium, "a stoppage." Following the winter solstice, the days begin to grow longer and the nights shorter.

File this under: Brought to you by the Scientific Method... a rigorous, systematic use of observations and logic to attempt to support or falsify possible explanations of natural phenomena.