The winter solstice occurs on Monday, December 21st, 2009, at 10:47 am, MST.
Solstice means sun stationary. This event marks the time when the sun is at its furthest point south of the celestial equator. The celestial equator is simply a projection of Earth’s equator out into space, and divides the sky into the northern celestial sphere and the southern celestial sphere.
The path of the sun against the background stars is called the ecliptic. As the sun moves along the ecliptic, it crosses the celestial equator at the autumnal equinox in September, then gets progressively farther south of the celestial equator until the winter solstice in December. At this point the sun is at its lowest in the sky. The days are short, the nights long, the air is cold. The sun rises well south of east and sets in the southwest. All points on or north of the Arctic Circle experience 24 hours of darkness, with no sunrise or sunset, on the solstice. The North Pole experiences 24 hours of darkness for 6 months, with the winter solstice as the mid-point of that time frame.
Many traditional Christmas events, activities and decorations originated in the celebration, fear and/or worship of the sun on this longest night of the year. Evergreen trees all lit up, holly, mistletoe and great fires are all indicative of the yearning to end the declining sunlight and anticipate the eventual return of life to the earth in spring. Though winter is just beginning, and the coldest days are yet to come, the days will slowly lengthen from this point on, as the sun climbs higher and higher in the sky.
In the southern hemisphere the seasons are reversed. The sun is still at its furthest south in the sky, but to those in the southern hemisphere, this means the sun is at its highest point in the sky. Summer is beginning. Antarctica is bathed in 24 hours of sunlight.