(CNN) — For six months, the days have been getting shorter and the nights getting longer in the northern hemisphere. But that’s about to reverse.
Winter solstice 2022, the shortest day of the year and the first official day of winter, is Wednesday, December 21 (well, for much of the world anyway). How it all works has fascinated people for thousands of years.
We will first look at the science and the precise moment behind the solstice. Next, we’ll explore some ancient traditions and celebrations around the world.
The science and timing behind a winter solstice
The winter solstice marks the shortest day of the year and the longest night in the northern hemisphere, when the sun appears at its southernmost position, directly above the Tropic of Capricorn.
The situation is reversed in the southern hemisphere, where only about 10% of the world’s population lives. There, the December solstice marks the longest day of the year – and the start of summer – in places like Argentina, Madagascar, New Zealand and South Africa.
These three images from NOAA’s GOES East (GOES-16) satellite show us what Earth looks like from space near the winter solstice. The images were captured around 24 hours before the 2018 winter solstice. You can see how the northern hemisphere is blanketed in more darkness.
When does it happen exactly?
The solstice usually – but not always – occurs on December 21. The date on which the solstice occurs may change because the solar year (the time it takes for the sun to reappear in the same place as seen from Earth) does not correspond exactly to our calendar year.
The sun sets at Ocean Beach in San Francisco on the 2020 winter solstice.
Jane Tyska/Digital First Media/East Bay Times/Getty Images
Below are some examples of when 9:48 PM UTC will correspond to different local times in locations around the world. Due to time zone differences, the vast majority of Asia will mark the winter solstice on Thursday, December 22.
• Tokyo: 6:48 a.m. Thursday
• Hanoi, Viet Nam: 4:48 a.m. Thursday
• New Delhi: 3:18 a.m. Thursday
• Istanbul: 12:48 a.m. Thursday
• Jerusalem: 11:48 p.m. Wednesday
• Copenhagen, Denmark: 10:48 p.m. Wednesday
• Charlotte, North Carolina: 4:48 p.m. Wednesday
• Winnipeg, MB: 3:48 p.m. Wednesday
• San Francisco: 1:48 p.m. Wednesday
• Honolulu: 11:48 a.m. Wednesday
Which places see and feel the effects of the winter solstice the most?
Daylight decreases significantly as you get closer to the North Pole on December 21.
The illuminated Pont Alexandre III spans the Seine, adding to the magic of Paris in winter.
Frédéric Soltan/Corbis News/Getty Images
What causes the winter solstice to occur?
Because the Earth is tilted on its axis of rotation, we have changing seasons. As the planet moves around the sun, each hemisphere experiences winter when it is tilted away from the sun and summer when it is tilted toward the sun.
Hold! Why is the Earth tilted?
Scientists aren’t sure exactly how this happened, but they believe that billions of years ago, as the solar system was taking shape, Earth was subjected to violent collisions that caused the tilt of the axis.
What other seasonal transitions do we mark?
The spring and fall equinoxes occur when the sun’s rays are directly overhead the equator. During these two days, everyone everywhere has a roughly equal duration of day and night. The summer solstice is when the sun’s rays are most northerly over the Tropic of Cancer, giving us our longest day and the official start of summer in the northern hemisphere.
Winter Solstice Traditions and Celebrations
A view of the Rockefeller Center Christmas tree for 2022. Many Christmas traditions have their roots in pagan celebrations.
John Lamparski/Getty Images
It’s no surprise that many cultures and religions celebrate a holiday – be it Christmas, Hanukkah, Kwanzaa or pagan holidays – that coincides with the return of longer days.
Ancient peoples whose survival depended on an accurate knowledge of seasonal cycles marked this first day of winter with elaborate ceremonies and celebrations. Spiritually, these celebrations symbolize the opportunity for renewal.
“Christmas takes many of its customs and probably its date from the pagan Roman holiday calendar of Saturnalia and Kalendes,” Maria Kennedy, an assistant professor in Rutgers University’s Department of American Studies, told CNN Travel in an email. -mail.
The Saturnalia began on December 17 and Kalendes started Jan. 1, said Kennedy, who specializes in Christmas studies.
Citing academic research, Kennedy said the early founders of the Christian church condemned the practices of these holidays, but their popularity endured. The Christian observance of Christmas eventually lined up around the same time in the calendar, even though there is no specific date set in the Gospels for Jesus’ birth.
Here is more about some of these ancient customs:
In ancient Rome, Saturnalia lasted seven days. It honored Saturn, the Roman god of agriculture.
It wasn’t just the ancient Europeans who marked the annual occasion. The Dongzhi Winter Solstice Festival has its roots in ancient Chinese culture. The name roughly translates to “extreme winter”.
Many places around the world traditionally hold festivals that honor the winter solstice. A few of them include:
A choir sings at Stonehenge to mark the winter solstice.
Ben Birchall/PA Images/Getty Images
CNN’s Katia Hetter and Autumn Spanne contributed to this article.