The solstices occur due to the Earth's axial tilt of approximately
23.5 degrees relative to its orbital plane around the Sun. This tilt
causes different parts of the Earth to receive varying amounts of
sunlight throughout the year, leading to the changing seasons.
During the winter solstice, one hemisphere is tilted the farthest
away from the Sun, resulting in the shortest period of daylight.
At the exact moment of the solstice, the Sun reaches its lowest
maximum elevation in the sky. In the Northern Hemisphere, this
happens around December 21st or 22nd, when the Sun is directly over
the Tropic of Capricorn at 23.5 degrees south latitude.
The solstice is a precise moment in time, but its effects are felt
throughout the day. The term "solstice" comes from the Latin words
"sol" (sun) and "sistere" (to stand still), because the Sun's
apparent movement north or south comes to a stop before reversing
direction.