EarthSky’s page on the winter solstice says:
The solstice happens at the same instant for all of us, everywhere on Earth. In 2016, the December solstice comes on December 21 at 5:44 a.m. EST. That’s on December 21 at 10:44 Universal Time. It’s when the sun on our sky’s dome reaches its farthest southward point for the year. At this solstice, the Northern Hemisphere has its shortest day and longest night of the year.
…At the December solstice, Earth is positioned in its orbit so that the sun stays below the north pole horizon. As seen from 23-and-a-half degrees south of the equator, at the imaginary line encircling the globe known as the Tropic of Capricorn, the sun shines directly overhead at noon. This is as far south as the sun ever gets. All locations south of the equator have day lengths greater than 12 hours at the December solstice. Meanwhile, all locations north of the equator have day lengths less than 12 hours.
For us on the northern part of Earth, the shortest day comes at the solstice. After the winter solstice, the days get longer, and the nights shorter. It’s a seasonal shift that nearly everyone notices.