The winter solstice, which many use to mark the official start of winter, is Wednesday, December 21 2016 at 10:44 UTC, 2:44am PST. Today is the first day of winter and it will be the shortest day and longest night of the year in the Northern Hemisphere, just nine hours, 32 minutes of daylight and 14 hours and 28 minutes of nighttime. The sun appears at its lowest point in the sky, and its noontime elevation appears to be the same for several days before and after the solstice.
The word solstice comes from the Latin words for “sun” and “to stand still.” In the Northern Hemisphere, as summer advances to winter, the points on the horizon where the Sun rises and sets advance southward each day; the high point in the Sun’s daily path across the sky, which occurs at local noon, also moves southward each day. At the winter solstice, the Sun’s path has reached its southernmost position. The next day, the path will advance northward. However, a few days before and after the winter solstice, the change is so slight that the Sun’s path seems to stay the same, or stand still. The Sun is directly overhead at “high-noon” on Winter Solstice at the latitude called the Tropic of Capricorn. The Winter Solstice can happen on December 20, 21, 22 or 23, though December 20 or 23 solstices are rare. The last December 23 solstice was in 1903 and will not happen again until 2303.
If it feels like winter has already begun, you are correct. Meteorologists consider Dec. 1 the start of the meteorological winter and March 1 the start of the meteorological spring. That’s because December, January and February are the three coldest months of the year. By the time the Spring Equinox rolls around on March 20, 2017, average temperatures in most areas will have already started rising. The winter solstice isn’t the coldest day of the year, either — that comes later.