Shortest, or longest, day of the year
On December 21, at precisely 15:59 UTC, the Sun will be directly above the Tropic of Capricorn. This celestial event is the December solstice, and it is the farthest south the Sun reaches during the year. Now it begins moving north again.
At the solstice, the Northern Hemisphere's tilt away from the Sun is greatest, making it the shortest day of the year north of the equator. The opposite happens south of the equator: Earth is tilted towards the Sun, making it the longest day of the year in the Southern Hemisphere.
The Full Moon on December 19 at 04:35 UTC will be a little over 405,000 km (252,000 miles) away from Earth—making it a Micromoon.
Because the Moon orbits Earth in an elliptical path, one side of the path is closer to the Earth than the other. When a Full Moon occurs around its farthest point from Earth—its apogee—it is known as a Micromoon.