The days can only get longer for six months Hooray.
The winter solstice happens because the Earth does not spin upright, but on an axis 23.5 degrees from vertical. As the Earth orbits the sun, it reaches the moment of winter solstice when the north pole is tilted furthest from the sun, making it the shortest day of the year. The winter solstice is as far south as the sun ever gets, shining directly overhead along the Tropic of Capricorn, 23.5 degrees south of the equator. Usually, the winter solstice occurs on the 21 December, but that can shift for the same reasons we have leap years: the Earth takes 365.25 days to orbit the sun, but the Gregorian calendar has only 365 days so each year the solstice is pushed back by around six hours.