As the year opens, it's worth taking a moment to reflect on the subject of time.
Time-keeping is complicated. A great example is the recent movement of the international date line to put Samoa and Tokelau on the other side, as the U.S. declines in relative importance as a trading parter compared to Australia, New Zealand, and China.
Time exists at the intersection of cosmology, biology, culture, politics, economics, and technology. The cosmological aspects of time are tricky enough, with at least two different but useful ways to define a year, the "solar year" (or" tropical year"), and the "sidereal year". Neither year works out to an even number of days -- and there are slightly different ways to define "day", as well.