When the sun is directly overhead at the tropic of Capricorn (23 1/2, 0) on 22nd December, the Northern Hemisphere experiences it’s

On December 22nd, the sun shines directly over the Tropic of Capricorn in the south. The Northern Hemisphere is tilted away from the sun.

This makes December 22nd the shortest day of the year in the north. It is called winter solstice.

While the north has winter, the south has summer solstice with its longest day.