When is the winter solstice? At sunrise this morning, about 15,000 people gathered at Stonehenge -- the world's most famous neolithic monument -- to mark the arrival of astronomical winter in the Northern Hemisphere.
The 5,000-year-old stone circle in Wiltshire, England, U.K., sees an annual alignment on the day of the solstices, with Dec. 21 this year seeing sunrise appear in the northeast just above the Heel Stone. The event was broadcast live on YouTube by English Heritage, with the global moment of solstice following soon after at 9:21 a.m. GMT (4:21 a.m. EST).
What does a solstice mean? The moment of solstice occurs when the sun reaches its southernmost point directly above the Tropic of Capricorn. At this moment, the sun appears to "stand still" before reversing direction, a phenomenon reflected in the Latin roots of the word solstice -- sol (sun) and sistere (to stand still).
What happens on the solstice? The sun rises at its farthest northeast position on the horizon of the year on the date of the winter solstice in the Northern Hemisphere.
Why is Dec. 21 the winter solstice? December's solstice occurs because Earth's axis is tilted by approximately 23.5 degrees relative to its orbit around the sun. On Dec. 21, the Northern Hemisphere is tilted the farthest away from the sun, resulting in shorter daylight hours and colder temperatures. The sun appears lower in the sky and takes a shorter path through it.
This year, the event coincided with new research that suggests that Stonehenge may have been constructed as a unifying landmark in prehistoric times. The new theory posits that the monument's stones, sourced from distant regions, served as symbols of political alliances, possibly after unrest.
According to a paper published in Archaeology International, rather than being a temple, a calendar or an observatory -- as many archeologists have theorized -- Stonehenge is political. "I think we've just not been looking at Stonehenge in the right way," said Mike Parker Pearson of University College London, the paper's author, to The Guardian. "You really have to look at all of it to work out what they're doing. They're constructing a monument that is expressing the permanence of particular aspects in their world." Solstice alignments may have a less important purpose.
Earlier this year, another scientific paper provided compelling evidence that Stonehenge's central altar stone originally came from about 430 miles (700 kilometers) away in the north of Scotland. In 2021, archaeologists pinpointed the origin of the stone circle's smaller bluestones as Pembrokeshire in Wales, about 180 miles (290 kilometers) west of Stonehenge.