Saturday is the winter solstice and 2024's shortest day. Here's what to know about the official start of winter.

The 2024 winter solstice, the shortest day of the year, happens on Saturday, Dec. 21, in the Northern Hemisphere. The celestial event signifies the first day of winter, astronomically. 

The winter solstice is the day each year that has the shortest period of daylight between sunrise and sunset, and therefore the longest night. It happens when the sun is directly above the Tropic of Capricorn, a line of latitude that circles the globe south of the equator, the National Weather Service explains.