Winter officially begins on Sunday, December 21, 2025, with the winter solstice, marking the shortest day and longest night of the year for the Northern Hemisphere. This astronomical event occurs because of Earth's axial tilt, positioning the North Pole at its farthest point from the sun. As a result, the amount of daylight is minimized, signaling the commencement of winter. The exact date of the winter solstice can vary, typically falling between December 20 and 23, most commonly on the 21st or 22nd.