Winter solstice marks start of astronomical winter in Northern Hemisphere

Sunday marks the winter solstice in the Northern Hemisphere, the shortest day of the year and the official start of astronomical winter. In the Southern Hemisphere, the solstice brings the longest day and the start of summer. The solstice is a moment when the tilt of the Earth's axis away from the sun reaches its maximum, producing the sun’s lowest arc across the sky. The date can vary by year; this year the solstice falls on Dec. 21.

During the winter solstice, the Northern Hemisphere is tilted the farthest away from the sun, yielding the shortest daylight and the longest night of the year. The sun's daily arc reaches its southernmost point at solar noon. The solstice typically occurs sometime between Dec. 20 and Dec. 23, and in 2025 it arrives on Dec. 21.

After the solstice, daylight begins to lengthen slowly. In many places, the increase in daylight is measured in minutes per day, with the days continuing to brighten until the summer solstice in late June. The Northern Hemisphere's summer solstice typically falls between June 20 and 22, when the sun reaches its highest point in the sky at noon.

The solstice's name comes from Latin sol (sun) and stitium (pause or stop), describing the moment when the sun's path pauses before reversing its direction. The related term equinox comes from Latin words meaning equal night, since day and night are nearly the same length on those days. Equinoxes occur in autumn and spring: the autumnal equinox can land between Sept. 21 and 24, while the vernal (spring) equinox can land between March 19 and 21. These dates are used to describe astronomical seasons; meteorological seasons, by contrast, are split into three-month blocks based on temperature cycles, with winter defined as December 1 through February 28.

These seasonal markers reflect Earth’s tilt and orbit, not weather. They have shaped calendars and cultures for millennia, from agricultural planning to celebrations and monuments aligned with the sun’s paths at the solstices. Stone circles and other ancient structures across the world have been associated with solstice alignments, underscoring a long history of observing the sun’s cycles.

In practical terms, the solstice today signals a turning point, even as the weather remains variable by region. For many observers, the days will gradually grow longer after Dec. 21, though the pace of change depends on latitude and local cloud cover. The Sun’s return toward higher midday elevations promises progressively longer daylight hours, a pattern that will continue through the spring and into summer.

Sunday’s solstice also serves as a reminder of the broader astronomical framework: the Earth travels around the Sun in an elliptical orbit while its axis remains tilted. This combination produces the seasonal contrasts that define life in both hemispheres, even as climate patterns shift with time.