In 2022, winter The solstice for the northern hemisphere occurs on December 21. Although it is not as dramatic as that of 2020 conjunction of Jupiter and SaturnThe longest night of the year is an important turning point. astronomical winter It begins and the days slowly become longer.
Curious why this happens? WIRED spoke with Tansu Daylanformer postdoctoral associate on the Transiting Exoplanet Study Satellite (TESS) at MIT, to better understand the winter solstice and our planet’s relationship with the sun.
To imagine what happens in space during a winter solstice, let’s start by thinking of a giant crystal ball surrounding the Earth and 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 on this celestial sphere, known as the ecliptic plane.” .
“As it does so, the sun changes its declination,” he says. Decline and right ascension They are the two main axes of the celestial sphere. “In this frame of reference, the sun is at the southernmost location 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 most tilted toward the sun. The Arctic Circle is shrouded in darkness and experiences the longest night of the year. In the southern hemisphere, a summer solstice occurs simultaneously with the south pole tilted toward the sun and the Antarctic Circle experiencing midnight sun.
NASA’s Spaceflight Basics online tutorial includes a section on celestial sphere with illustrations for anyone who enjoys exploring the idea further.
The low position of the sun during a winter solstice will cause its midday shadow be exceptionally long. Although important to humans, a solstice doesn’t have much meaning with respect to the cosmos at large.
“The solstices are defined with respect to the Earth-sun system, not necessarily the entire solar system. We give it a lot of meaning because the sun is very sacred to us and its location in the celestial sphere, depending on the weather throughout the year, is very important,” says Daylan. “It sets the mood. Throughout the year it tells us when the crops will mature. “That is very important, especially for historical civilizations.”