As the Earth travels around the Sun in its orbit, the north-south position of the Sun
changes over the course of the year due to the changing orientation of the Earth's
tilted rotation axes with respect to the Sun.
In the northern hemisphere, the Winter solstice is day of the year (near December 22)
when the Sun is farthest south. However, in the southern hemisphere, winter and summer
solstices are exchanged so that the winter solstice is the day on which the Sun is
farthest north. The winter solstice marks the first day of the season of winter.
The winter solstice is the shortest day of the year, respectively, in the sense that
the length of time elapsed between sunrise and sunset on this day is a minimum
for the year.