The first day of winter—the (December 21 or 22)—is the shortest day and the longest night of the year. In the Northern Hemisphere, the sun is at its lowest point in the sky.
There isn't actually just one "first day." Scientists and meteorologists use two different systems to define when a season begins: first day of seasons
You might notice that the first day of a season isn’t on the same date every year. This is because a "year" isn't exactly 365 days; it actually takes the Earth about 365.242 days to orbit the sun. Our calendar accounts for this with Leap Years, which causes the astronomical timing of the solstices and equinoxes to drift slightly between the 20th and 23rd of their respective months. The first day of winter—the (December 21 or
Meteorologists and climatologists find the astronomical dates a bit messy because they change slightly every year (falling between the 20th and 23rd). To keep records consistent, they break the seasons into three-month blocks based on the annual temperature cycle: Spring: March 1 Summer: June 1 Autumn: September 1 Winter: December 1 Spring: The Vernal Equinox This is because a "year" isn't exactly 365
Most people know that summer is hot and winter is cold, but the "First Day" of a season is defined by a specific geometric relationship between the Earth and the Sun.