It’s the First Day of Winter
The December solstice occurs at 22:23 UTC. The South Pole of the earth will be tilted toward the Sun, which will have reached its southernmost position in the sky and will be directly over the Tropic of Capricorn at 23.44 degrees south latitude. This is the first day of winter (winter solstice) in the Northern Hemisphere and the first day of summer (summer solstice) in the Southern Hemisphere.
The Sun is directly overhead of the Tropic of Capricorn in the Southern Hemisphere during the December Solstice.
The December Solstice occurs when the Sun reaches its most southerly declination of -23.4 degrees. In other words, when the North Pole is tilted furthest away from the Sun.