December 21 st marks the first official day of winter – and the winter solstice – the longest night of the year. According to Rick Kline of the Spacecraft Planetary Imaging Facility at Cornell University, solstices and equinoxes denote either the beginnings of the seasons or the center points of them. Kline tells USA Today that Christmas, Hanukkah, Kwanzaa and other holidays have arisen out of just these markings. Whether you celebrate the season by sitting around the Christmas tree, sipping hot