In December, the Earth's north pole tilts furthest away from the sun, meaning that the sun rises later, sets earlier, and never rises very high in the northern hemisphere skies. The day the sun's at its lowest, the winter solstice, is when many, many cultures around the world have festivals of light: Christmas, Hanukkah, St. Lucy's Day, Yule, Saturnalia, Dongzhi, and Yalda, among others. Often times people find it odd that some of the most joyous holidays of the year are held on or around the shortest, darkest day of the year, but upon a moment of reflection they realize that the solstice also marks the time that days begin to get longer, and light begins to return to the world.