What is the official first day of winter in the Northern Hemisphere?

The official first day of winter in the Northern Hemisphere is December 21st. This date corresponds to the winter solstice, when the North Pole is tilted furthest away from the Sun. As a result, this day experiences the shortest amount of daylight and the longest night of the year. The winter solstice not only marks the beginning of astronomical winter but also holds significant cultural importance in many societies, often celebrated with various festivals and traditions.

The other dates listed do not coincide with the astronomical definition of winter. January 1st is simply the start of a new calendar year and does not have any astronomical significance related to winter. November 21st is not recognized in the astronomical calendar as winter begins, and February 21st occurs well into the winter season, closer to the spring equinox, which signals the end of winter in the Northern Hemisphere.