For six months each day has been shorter than the last and the Sun lower in the sky. Will it disappear altogether and leave the people bereft in the dark cold winter? The winter solstice is the shortest day of the year and is associated with more festivals than any other astronomical event.
Winter Solstice
Over the year, the Sun's position in the sky changes. Taking a a set of pictures that include the Sun at the same time and location, the Sun positions would make a figure-8. We call that an analemma. In an analemma, the winter solstice day is at the bottom of the figure, because the Sun is lowest in the sky then.
This analemma, (shot by Cenk E. Tezel & Tunç Tezel, includes the totally eclipsed Sun during a solar eclipse. Wow! And since the eclipse is near the crossing point of the analemma, you can tell that it happened near an equinox. In fact, it was on March 29th, soon after the northern hemisphere spring equinox.
Today – December 21, 2014 – is the day of the winter solstice in the northern hemisphere, the summer solstice in the southern hemisphere. Astronomically, this solstice is the precise time when the Sun is over the Tropic of Capricorn and the poles are at their maximum tilt in relation to the Sun.
That will happen today at 11:03 PM UTC, which is the same as Greenwich Mean Time at this time of year. In New York, it will be five hours earlier at 5:03 PM. But for time zones east of the Greenwich Meridian, the solstice will occur on December 22nd.
By the way, even though this is the shortest day in the northern hemisphere, the mornings will still get darker for a few weeks. Earth's orbit isn't a perfect circle and we move at fluctuating speeds in orbit. So the Sun may lag behind the clock or be ahead of it, but it works out on average!