Today is the first day of winter and the Winter Solstice. It is the shortest day for the Northern Hemisphere. The Winter Solstice usually falls between December 20-23 and the sun is directly overhead the Tropic of Capricorn resulting in the North Pole being tilted the furthest away. The result is shorter days for sunlight for the Northern Hemisphere. And the further north you are (like Alaska or Scandinavian countries) means less sun during the day. The reverse happens in the Southern Hemisphere as the sun is closer to them and they celebrate the Summer Solstice. Those closer to the South Pole can have nearly 24 hours of sun during this time of year.
Many cultures observed the Winter Solstice as it marked an important time in the agricultural cycle. By this time all crops and livestock had been prepared for winter. Important foodstuffs were stored for the months when virtually nothing grew. Wine and beer, which had been fermenting during the year, was ready at this time. Cattle and pigs would often be killed at the start of winter so they would not have to be fed during this time. The early months of winter were tough in many places and often called the “famine months” since little food was to be found. Many cultures observed the Winter Solstice as a renewal or that the year was reborn. For out of the seeming withdrawal of the sun, it would come back just as strong and powerful as before. Thus the Winter Solstice was seen by many as the start of a new year such as the old Roman Feast of the Unconquered Sun (Sol Invictus) which happened around the 25th of December.
For those who watch the calendar, today marks the official end of summer and the beginning of autumn with the equinox today. It begins today at 13:30 UTC (go here to see the time it begins in your area). There are two equinoxes in the year: March and September. When these equinoxes occur the sun is directly on the equator, and the length of day and night is almost equal. In the Northern hemisphere, the September Equinox heralds autumn while in the South it is the beginning of spring.
For those of us in the North, it means a transition from summer to winter. During this period days start getting shorter and nights longer. Depending on where you live, you will likely have moderate warm days followed by long and cooler nights. Harvests of many crops often take place during the fall and in the old days you would make preparations to store food for the winter. Harvest festivals are very popular and in particular Halloween. Pumpkins begin appearing along with all kinds of Halloween decor culminating, of course, in All Hallows Eve (Halloween) on October 31.
Today is the Summer Solstice in the Northern Hemisphere. For those below the equatorial line, it is the Winter Solstice. The June Solstice usually takes place between June 20-22. For those in the Northern Hemisphere, it usually is the longest day of sunlight as the North Pole tilts directly towards the sun. Which translates into more sunlight particularly the further north you live. For those more closer to the North Pole (Alaska, parts of Canada, and Scandinavian countries)the sun literally never sets during this time of year. Of course the reverse is true in the Southern Hemisphere. They get less sunlight on the June Solstice and the closer you are to the Antarctic Circle means less sunlight or total night.
The coming of summer is usually a time for celebration in many cultures. Festivals in Northern Europe celebrate summer and the fertility of the Earth. Bonfires are lit and homes are decorated to mark the festival. Many cultures honor the sun in some fashion. Modern day pagans and druids also celebrate the day with their own festivals and many go to Stonehenge in England to witness the first rays of summer.