It's hard to realize the move from fall to winter when temperatures don't cooperate. Regardless, tonight the transition to the coldest part of the year begins.
At 11:19 p.m. EST today, the sun’s direct rays will touch the Tropic of Capricorn (23.5⁰ south of the equator). Due to this phenomenon, we experience the shortest days and longest nights of the year as well as the lowest sun angles.
This year the solstice will hit late in the evening, leading to both today and tomorrow being nearly equal in length. This means we get two “shortest days of the year.” They will be less than a second apart in time, both totaling 9 hours, 31 minutes, and 25 seconds long. This day length is 5 hours and 17 minutes shorter than the June solstice day length. From here, day length will increase slowly at first by only a few seconds each day. By the spring equinox, we will be adding about 2 minutes and 28 seconds. After that point, the time added to each day becomes less, and down to mere seconds as we get near the summer solstice.
The solstices (and seasons for that matter) are a direct result of the tilt of the earth’s axis. As the earth revolves around the sun, the tilt of the earth is either oriented towards, away, or direct with the sun’s rays. When the northern hemisphere is oriented away from the sun’s direct rays, colder air can infiltrate further south bringing colder temperatures.