On Mon, Oct 22, 2018 at 2:12 AM Mark H Weaver <m...@netris.org> wrote:
Universal Time (UT) is not a measure of physical time, but rather is a > measure of the rotation angle of the Earth with respect to distant > quasars. A UT second is identified with a fixed amount of rotation of > the Earth, which equals 1/86400 of a mean solar day. That's why every > day has 86400 UT seconds. Quite right. Buit the whole point of UTC is that its seconds are not angles, but SI = TAI seconds. There are a variable number of these in a day, and a UTC clock will indeed report 23:59:60 at the end of a day with a leap second in it (and other civil-time clocks will similarly report :60 in whatever hour, according to their timezone offsets). See <https://en.wikipedia.org/wiki/Leap_second#/media/File:Leapsecond2016.png>, which is a screenshot of https://time.gov displaying the last leap second. Now there are indeed exactly 86400 _Posix_ seconds in a day, which is achieved by giving two seconds the same label if it is a leap day. But that has nothing to do with either TAI or UTC. > UTC is kept within 0.9 seconds of UT1 (a > version of UT with certain corrections applied), so over long time > periods, with the leap seconds taken into account, UTC seconds are equal > to UT seconds. > No, in the long run UTC time is equal to UT1 time. That's not the same thing at all. -- John Cowan http://vrici.lojban.org/~cowan co...@ccil.org I am expressing my opinion. When my honorable and gallant friend is called, he will express his opinion. This is the process which we call Debate. --Winston Churchill
