The winter solstice heralds the astronomical start of winter and marks the day with the fewest hours of daylight for the year. In 2024, the winter solstice happens on Saturday, Dec. 21 at 4:21 a.m. EST in the Northern Hemisphere. But what's the science behind the shortest day and longest night?
The winter solstice — and for that matter, the four seasons — occur because Earth is tilted at an angle of about 23.5 degrees relative to the sun. Instead of rotating on a straight axis, our planet is "tipped a bit," said Michael S. F. Kirk, a research astrophysicist in the Heliophysics Science Division at NASA's Goddard Space Flight Center in Greenbelt, Maryland.
