in the Northern Hemisphere is today, December 21. The sun, so we were told in elementary school science class, will appear to stand directly over the Tropic of Capricorn on this day. This is a result of the earth's transit of the sun and the inclination of its axis.* This marks the day of the year with the fewest sunlight hours, and the official beginning of "winter."
And now that I have sufficiently confused everyone (not because the facts are misrepresented, but because of my inept explanation) we may all get on with our lives. For marking this event is in reality just another day in the life.
*Note: We learned in school that the Earth's "tilt," or deviation of the axis of rotation from perpendicular to the plane of Earth's orbit is 23-1/2 degrees, a conveniently remembered number. In reality, the current deviation is 23.44 degrees, and this varies over time from 22.1 to 24.5 degrees, which has a real effect on the weather, the climate, the variations between summer and winter temperatures.