Each year, the winter solstice signals the "beginning" of the winter season. But just what is this winter solstice and why is it so significant?
The winter solstice is the day during which the sun is at its most Southern point in the sky (usually near December 22nd). Consequently, it is also the shortest day of the year, having the longest night. The word solstice itself comes from a Latin phrase meaning "the Sun stands still". For a few days before and after solstice, the sun would be changing declination so slowly that it would appear to be standing still.
The easiest way to visualize this is to imagine yourself standing on a sphere (the Earth). If you're standing in the Northern hemisphere, the sun will always appear to be slightly South of your location. The more you tilt the North pole away from the sun, the further South the sun seems to dip. The tilt of the Earth's axis is not changing, but its position relative to the Sun is, producing the same effect.
Since the solstice marks the reversal of lengthening nights and shortening days, many cultures assign it great significance. Artifacts such as Stonehenge and New Grange show that the solstices were an important date as far back as the Bronze Age. Many cultures see the winter solstice as a "rebirth" of the sun, and as such many holidays too numerous to list here seem to be centered around it. Perhaps this is because as the days get longer, our moods are becoming more positive as we look forward to the longer days.
The winter solstice occurs on the following days in upcoming years: