2022, the winter The solstice for the northern hemisphere occurs on December 21st. Though not as dramatic as the conjunction of Jupiter and Saturn in 2020, the longest night of the year is a significant turning point. The astronomical winter is beginning and the days are gradually getting longer again.
Curious why this is happening? WIRED spoke to Tansu Daylan, a former Transiting Exoplanet Survey Satellite (TESS) postdoctoral fellow at MIT, to better understand the winter solstice and our planet’s relationship to the sun.
To visualize what happens in space during a winter solstice, first think of a giant glass sphere surrounding the Earth and let’s ignore the planet’s rotation (which complicates everything). Daylan says, “If you look at the three-dimensional sphere around us, known as the celestial sphere, the Sun, as well as all other objects in the solar system, move through a plane in this celestial sphere known as the ecliptic plane.”
“The sun changes its declination,” he says. Declination and right ascension are the two main axes of the celestial sphere. “In this frame of reference, the sun is at its southernmost point when it is the winter solstice from our perspective in the northern hemisphere.”
A winter solstice in the northern hemisphere occurs when the North Pole is furthest from the sun. The Arctic Circle is shrouded in darkness and experiences its longest night of the year. A summer solstice occurs simultaneously in the southern hemisphere, when the South Pole is tilted toward the sun and the Arctic Circle experiences the midnight sun.
NASA’s Astronautics Basics online tutorial has a section on the celestial sphere with illustrations for anyone who’d like to explore the idea further.
The low position of the sun during a winter solstice causes your midday shadow to be exceptionally long. While important to humans, a solstice doesn’t mean much in the larger cosmos.
“The solstices are defined in terms of the Earth-Sun system, not necessarily the entire solar system. We attach great importance to it because the sun is so sacred to us and its position on the celestial sphere as a function of time throughout the year is very important,” says Daylan. “That determines the climate. All year round it tells us when the harvest is ready. So this is very important, especially for historical civilizations.”
From the yuzu baths in Japan to the Inti-Raymi celebrations in Peru, cultures around the world have a long tradition of celebrating the winter solstice. Contemporary druids and archaeologists in England continue to fixate on the Stonehenge monument at this time of year. The interests of the two groups occasionally align, but they often disagree on issues such as displaying human remains found at Stonehenge.
https://www.wired.com/story/winter-solstice/ What’s the Winter Solstice, Anyway?