HAPPY WINTER SOLSTICE!

In the Northern Hemisphere the winter solstice occurs when the Sun is at its greatest distance from the earth's equator and falls on either December 21 or 22 when the sun shines directly over the tropic of Capricorn.  The summer solstice occurs on June either June 20 or 21 when the sun shines directly the tropic of Cancer.  In the Southern Hemisphere the solstices are reversed.

The winter solstice also represents the shortest day of the year while the summer solstice represent the longest day of the year.  Many cultures and religions have festivals, celebrations, and gatherings around this time of year.  Keeping track of the time of year is not a new invention as it was extremely important for crop production and such.  Many archaeological sites are identified with keeping track of the summer and winter solstice.  One of the most famous being Stonehenge in England.

sources:
wikipedia
infoplease