Earth in Space: Northern Hemisphere Winter Solstice
This sketch shows Earth in space at the time of the Northern Hemisphere Winter Solstice. The Sun is located far to the left of the sketch, so its rays arrive essentially parallel to one another.

At this time the terminator is tangent to the Arctic and Antarctic Circles.

The Sun is directly overhead and the sub-solar point is at its southernmost latitude on the Tropic of Capricorn (23.5° S latitude).

This is the shortest period of daylight of the year in the Northern Hemisphere; the longest period of daylight of the year in the Southern Hemisphere.

The region in which
night time darkness is present continuously for 24 or more hours is contained within the Arctic Circle (67.5° N latitude) and is at its greatest extent; on the Arctic Circle, darkness lasts for 24 hours, then the Sun rises and the days begin to grow longer as the cap of darkness begins to shrink.

daylight is present continuously for 24 or more hours is contained within the Antarctic Circle (67.5° S latitude) and is at its greatest extent; on the Antarctic Circle, daylight lasts for 24 hours, then the Sun sets and the days begin to shorter as the cap of continuous daylight begins to shrink.
Similar events characterize the Summer Solstice.