Sun Time

. In mid-January my spouse mentioned that she was happy to have increasing daylight after work, now that we were past the Winter Solstice. Then she said "How come it's still just as dark in the morning, the sunrise time stays the same." Junior scientist that I am I boldly pronounced "No way. Nature is always symmetric." Guess who was wrong?
. The advance of sunset time in December is small, but it steadily increases to about a minute per day by early January.
. About sunrise though, I need to introduce one fact. The Sun's place against the background of stars (pretend it is eclipsed) changes. It moves East the equivalent of 2 minutes of daylight every day due to the motion of the Earth revolving around it. Comparing it to a clock, folklore says the "Sun runs slow." (There are other other uses for that expression, but save that for another time.)
. In the Spring the amount of daylight is increasing rapidly each day, so nobody notices this effect. But in the winter that 2 minutes is signifcant. Whatever advance of sunrise time is gained each day is knocked out in early January by the daily Sun-runs-slow effect, so the gain is added on at day's end and makes sunsets additionally later.
. Nutty as it sounds the earliest sunset around here is on December 9, not on the Solstice! From then on it advances, more and more daily. Also, amazingly, the latest sunrise is not on the Solstice, but on January 4! Then it does start to get earlier by a fraction of a minute, increasing daily. Not until month's end do we finally gain daylight by appreciable changes at both ends of the day. So she was right!