The Northern Hemisphere winter will begin on December 21st (Credit: Ernst Vikne/ CC-BY-SA-2.0/ Wikimedia Commons)

With the days getting increasingly shorter and colder, it may appear that winter is already upon us. However, the astronomical start of the chilly season in the Northern Hemisphere will not be until December 21, 2023. Often referred to as the winter solstice, it marks the shortest day and the longest night of the year. Conversely, Southern Hemisphere residents will celebrate the summer solstice on this day. They will enjoy the longest day and shortest night of 2023.

The different seasons are a result of Earth's rotation around the Sun and its own axis, which is tilted at a 23.5-degree angle. The December solstice marks the time when the Northern Hemisphere is farthest away from the Sun. Hence, it receives significantly less sunlight than the Southern Hemisphere, which is inclined towards the star.

During the winter solstice, Earth is tilted furthest away from the Sun (Credit: NASA/ JPL/ Public Domain)

The winter solstice was important for ancient cultures because the days became increasingly longer once it passed. While many months of cold weather remained, people knew the Sun had not abandoned them. They celebrated the Sun's "rebirth" on this day with elaborate ceremonies and even built unique structures.

Stonehenge in Wiltshire, England, is one of the most well-known. The prehistoric religious site comprises a modest circle of stones perfectly aligned with the Sun's movements. It is believed to have been constructed just for the solstice. Hundreds of people visit the ancient site on the winter solstice to commemorate Yule. It is one of the oldest known solstice-related celebrations.

Newgrange in Boyne Valley, Ireland, is also very popular. The 5,200-year-old giant stone structure is designed to receive a beam of light into its central chamber at sunrise on the winter solstice. The light illuminates the intricate carvings inside the structure for about 17 minutes. However, admission to the chamber is limited to just 20 people a day and is decided annually by lottery.

Many American cities have started their own winter solstice traditions. San Francisco, California, residents celebrate the occasion with a bonfire on Ocean Beach. Those living in Anchorage, Alaska, enjoy their 18-hour, 33-minute-long night with numerous fun activities. They include sleigh riding in the park, hiking the ice lantern-lit paths of the Eagle River Nature Center, and admiring the shimmering northern lights.

Happy Winter Solstice!