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. In the Southern Hemisphere, the winter solstice occurs
around
June 20th or
21st, when the Sun is over the Tropic of Cancer at 23.5 degrees north 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.