Winter solstice sunset (Photo Credit: Ennor, Flickr Creative Commons)

Though many meteorologists in the Northern Hemisphere consider December 1 as the first day of winter, the season's astronomical start is not till winter solstice that occurs on December 21 or 22 depending on the country's time zone. Southern Hemisphere residents of course experience the opposite and celebrate the first day of summer or summer solstice on these dates.

Though the entire day is observed, solstices occur at a specific time. The December or winter solstice that takes place when the sun is exactly overhead the Tropic of Capricorn will happen on December 22, at 0448 GMT (December 21 at 11:48 EST for residents of North America).

Photo Credit: srh.noaa.gov

Solstices and the distinct seasons in the two hemispheres are the result of Earth's rotation around the sun and its own axis that is tilted at an angle of 23.5 degrees. Though the direction of the tilt does not change as the earth moves around the sun, the position of the hemispheres do. During the December solstice, the Northern Hemisphere faces away from the sun, while the Southern Hemisphere tilts towards it. Hence, one-half of the planet experiences winter, while the other enjoys summer.

The day also marks the shortest (or longest) daylight period for the two hemispheres. However, it is not necessarily the latest sunrise or earliest sunset. Countries that lie in mid-altitudes experience the former in mid-January and the latter about two weeks before the solstice.

Though we now know the reason behind the long night, for ancient Northern Hemisphere civilizations the solstice signaled the turning point of the cold dark winters. As the days following the winter solstice got increasingly longer, it alleviated their fears that the energy-giving sun had abandoned them.

Newgrange entrance stone with megalithic art. (Photo Credit: Wikipedia Commons CC by SA 3.0)

They, therefore, celebrated the day with elaborate ceremonies and even built special structures. Among the most famous is Stonehenge. Located in Wiltshire, England, the pre-historic religious site that comprises a modest circle of stones is believed to have been specially constructed for winter solstice celebrations. Hundreds of people still make their way to the ancient site every year to commemorate Yule, one of the oldest known solstice-related celebrations

Another well-known destination for winter solstice celebrations is Newgrange in Boyne Valley, Ireland. The clever design of the 5,000-year-old massive stone structure allows the early morning winter solstice light to penetrate its 19-meter passage. As the sun rises, it lights up the dark chamber at the end of the passage, revealing incredible Neolithic rock art on its walls. The annual phenomenon that lasts for 17 minutes is so popular that viewing tickets are distributed by lottery.

Many cities around the world have also established their own winter solstice traditions. In San Francisco, California, citizens celebrate the occasion with hikes, bonfires, and even a dip in the freezing Pacific Ocean. Residents in Anchorage, Alaska, will spend the extra long (18 hours, 33 minutes) night with fun festivals and dances. Does your town or city have a winter solstice tradition? If so, be sure to share it with us by adding your comments below.

Resources: space.com, washingtonpost.com, timeanddate.com