Happy New Year
It is a new year, 2022. Happy New Year! Unlike Christmas, whose date has long since been settled (some say by Pope Julius I ), the date of the new year (i.e. the start of a calendar year) or even the notion what a "year" is has always been a bit murky. There are different kinds of "year." "Sidereal year" is the time Earth takes to orbit the Sun and come back to the position where stars are back in the same fixed alignment. The name comes from Latin "sidus," related to "asterism," or "star." That form of a year is approximately 365.256 days long, where "day" is defined as an "ephemeris day," which is exactly 86,400 SI seconds long. "Ephemeris" means "diary," but here it means "a book of tables with trajectories of astronomical objects." Such books have been in use for at least 3 thousand years, since the time of Babylonian astronomy . "Trop...