Winter Solstice occurs to mark the transition to winter from summer. The points on the horizon where the sun rises and sets advance southward each day, with it the high point in the sun’s daily path across the sky moves southward each day as well. At Winter Solstice this point reaches its southernmost position making it the shortest day of the year (December 21).

From the next day onwards the path now begins to move northward. The sun is directly overhead at the noon on Winter Solstice at the Tropic of Capricorn. Solstices are on opposite sides of the equator, so the Winter Solstice occurs in the Northern Hemisphere and Summer Solstice occurs in the Southern Hemisphere. 

The mating of animals, the sowing of crops and so on are astronomically guided with the help of the Winter Solstice. There are some cultural aspects to it as well. It is said that the Stonehenge in England and the Newgrange in Ireland were built over many centuries after observing in phases various solar and lunar astronomical events. The primary axes of both these monuments are seen to be carefully aligned on a sight-line. The Newgrange points to the Winter Solstice sunrise while the Stonehenge points to the Winter Solstice sunset. There are several theories that believe that the Stonehenge was constructed to be used as a temple to worship the Sun, as a royal burial ground or as a type of astronomical observatory. However, the validity of these has not been proven yet since the real reason for the construction of the Stonehenge still remains a mystery.

Winter solstice marked the beginning of the famine season in many parts of the world. In places with a temperate climate, it marked the onset of a deep winter and the end of festivities. At this time of the year, fresh meat would be available since cattle would be slaughtered so that they would not have been fed in the winter. The availability of wine and beer is also ample at this time as they have finally fermented. 

Iranians celebrate Winter Solstice as Yalda Night which is known as the longest and darkest night of the year. Families gather together to celebrate by eating, drinking and reading poems. They feast on nuts, pomegranates and watermelons especially.

The Scandinavians celebrated a twelve-day holiday around the Winter Solstice called Yule. It involves the modern day Christmas celebrations with the Christmas tree, the Christmas wreath, the Yule log and other such things which are direct descendants of the Yule traditions. This custom comes from a tribute poem to Harold Harfager from about 900 AD where someone said that drinking ‘Jul’ (Yule) is the most solemn sacrifice to earn God's blessings.

Sol Invictus (The Unconquered Sun) was a Syrian god who was later adopted as the chief god of the Roman Empire under Emperor Aurelian. His holiday is the one which is traditionally celebrated on December 25 as Winter Solstice associates many gods with it in pagan traditions. 

From traditions to now, what remains is the geographical explanation for Winter Solstice to be the shortest day of the year. The onset of winter is one to be celebrated in some places and feared in the others. As the North would say, “Winter is Coming.”