The winter season in the Northern Hemisphere began on December 1, 2021, while the summer season in the Southern Hemisphere began on December 1, 2021. For our planet’s two hemispheres, the December solstice brings in the astronomical winter and summer seasons, respectively. This will happen on December 21 at 15:59 UTC, which is 9:59 a.m. CST in the United States.
The solstices occur twice a year. In the Northern Hemisphere, the summer (June) solstice occurs around June 20-21, while the winter (December) solstice happens around December 21-22. Depending on which half of the world you’re on, the Sun’s path appears to be farthest north or south at the solstice. Seasons change on Earth because its axis is slightly inclined as it revolves around the Sun.
The Earth’s axis can be visualised as an imagined pole extending through the centre of our world from “top” to “bottom.” The Earth completes one full rotation around this pole every day. It is because of this that we have day and night.
Despite the Earth’s essentially constant tilt (23.5 degrees) in regard to the plane of its orbit around the Sun, the Northern Hemisphere receives the most indirect sunlight at the December solstice, resulting in colder temperatures. The Southern Hemisphere experiences summer because it receives the most direct sunlight, resulting in greater temperatures. At the June solstice, the Northern Hemisphere receives the most direct sunlight, while the Southern Hemisphere receives the most indirect sunlight, resulting in colder temperatures in both hemispheres.
The December solstice provides the shortest day and longest night of the year to locations in the northern half of the planet, such as the United States, while the longest day and shortest night are experienced by locations in the southern half of the globe. As a result, all sites north of the equator have shorter daylengths than those south of the equator, and all locations south of the equator have longer daylengths.
After the winter solstice in the Northern Hemisphere, the days will grow longer and the nights will grow shorter until the summer solstice on June 21, 2022, when the cycle will reverse. The astronomical spring season will begin on March 20, 2022, while the astronomical fall season will begin on September 22, 2022, with the September equinox on September 22, 2022.
According to ancient societies, the Sun’s route through the sky, the amount of daylight, and the location of sunrise and sunset all varied in a predictable rhythm throughout the year. People also created monuments, such as Stonehenge in England and the Torreon in Machu Picchu, Peru, to chart the Sun’s annual course and predict its movements.
We now know far more about the universe, and the solstice is recognised as an astronomical event caused by the Earth’s tilt on its axis and velocity in orbit around the Sun.
No matter where you are on the planet, this is your chance to celebrate the changing of the seasons!