Fall can be defined in two main ways: astronomical and meteorological. Astronomical fall in the Northern Hemisphere begins with the autumnal equinox, when day and night are approximately equal in length. In 2025, this occurs on Monday, September 22, and the season ends with the winter solstice on Sunday, December 21. So, astronomical fall 2025 runs from September 22 to December 21. Meteorological fall is based on the calendar months for ease of weather forecasting and statistics, starting on September 1 and ending on November 30. Thus, fall can be said to start either on:
- September 22 and end December 21 (astronomical definition)
- September 1 and end November 30 (meteorological definition)
Both definitions are widely used, but the astronomical definition aligns with Earth's position relative to the Sun, while the meteorological definition uses fixed calendar dates.
