Today marks the winter solstice (up here in the Northern hemi-sphere). As it turns out, we already had our earliest sunset : on December 11. (Check out the sunset in Fairbanks Alaska. One’s afternoon nap might as well turn into a loong full night’s sleep!). The reason is that there is a slight difference between the solar day (the time it takes for the sun to appear in the same position in the sky from one day to the next) and the calendar day. Here is the rest of the explanation from the Washington Post blog (hang in there): The Earth’s axis is tilted 23.5 degrees, and our orbit around the sun is elliptical (non-circular). In December, these two factors combine in such a way that our days are actually a few seconds longer than 24 hours – as seen by the amount of time it takes the sun to cross our local meridian (longitude) from one day to the next. In effect, this pushes the time of solar noon several minutes later during December, advancing both sunrise and sunset times even as the days continue to shorten until December 21.