Winter start dates vary depending on the definition used:
- Astronomical winter begins with the winter solstice, the shortest day of the year, around December 21 or 22 in the Northern Hemisphere. For example, in 2025, astronomical winter starts on December 21 and ends around March 20 of the following year. This is based on Earth's axial tilt and orbit around the Sun.
- Meteorological winter follows the calendar months and always starts on December 1 and ends on February 28 (or 29 in leap years). This system divides the year into four seasons of three full months each and aligns better with weather data and statistics.
Thus, winter can officially start either on December 1 meteorologically or around December 21 astronomically, depending on context and location.
