While the "first day of winter" printed on most calendars refers to the solstice, scientists and weather experts often use a more consistent system. 1. Astronomical Winter (The Solstice)
Astronomical seasons are based on the .
Meteorologists and climatologists divide the year into four equal seasons of three months each for easier record-keeping. Meteorological Versus Astronomical Seasons | News
Winter technically begins on two different dates depending on whether you follow an or meteorological definition.
Long ago, the transition into winter was a simple observation of the world's deep chill. But over time, two distinct groups—the sky-watchers and the record-keepers—developed their own "official" start dates.