Christmas is all about light. The nights are longer and magic. We use artificial lights to decorate our homes and cities as a wake up call for the Sun . It is the winter solstice, a date celebrated since time immemorial.

The winter solstice may have been immensely important in the past. It meant the sun was not going to continue to fade condemning the Earth to perpetual darkness, cold and death. However communities were not certain of living through the winter. Starvation was common in winter between January and April, also known as the famine months. Most cattle were slaughtered so they would not have to be fed during the winter, so it was almost the only time of year when a supply of fresh meat was available. The majority of wine and beer made during the year was finally fermented and ready for drinking at this time.

This year –2012– the days are getting longer and the nights shorter again since last Dec. 21 at 11:12 (UTC)., after the Earth’s rotation axis reached its maximum tilt to the Sun and began to recede.

The precise date of winter solstice changes every year due to the mismatch between the Earth’s revolution period around the sun and the rotation period around its own axis, which has created problems to define a sensible calendar strategy all along history.

In 46 BCE Julius Caesar  established December 25 in his Julian calendar as the date of the winter solstice in Europe Since then, the difference between the calendar year (365.2500 days) and the tropical year (~365.2421897 days) moved the day associated with the actual astronomical solstice forward approximately three days every four centuries, arriving to December 12 during the 16th century. In 1582, Pope Gregory XIII decided to restore the exact correspondence between seasons and civil year but, doing so, he did not make reference to the age of the Roman dictator, but to the Council of Nicaea of 325, as the period of definition of major Christian feasts. So, the Pope annulled the 10-day error accumulated between the 16th and the 4th century, but not the 3-day one between the 4th AD and the 1st BC century. This change adjusted the calendar bringing the northern winter solstice to around December 22. Yearly, in the Gregorian calendar, the solstice still fluctuates a day or two but, in the long-term, only about one day every 3000 years.

Happy winter solstice everyone!