On Sun, Feb 18, 2018 at 2:27 AM, Steve Allen <sla@ucolick.org> wrote:
On Sun 2018-02-18T00:08:25-0700 Brian Inglis hath writ:
Pretty presumptuous of the IAU to use Universal: they /should/ know better.
Alas, Universal Time of 1928 is a subdivision of the already approved Universal Day, and that derives from the Victorian-era knowledge of astronomy and speech patterns of the 1884 International Meridian Conference. Of regrettable things left over from time-keeping history, that is not the worst, and the Germans did explicitly avoid it by choosing Weltzeit as their term.
If Mars denizens decide to choose a single legal time scale that is constructed from an amalgam of precision time and planetary rotation then it will also need leaps of some sort. Hopefully they will avoid the attempt to bend a pre-existing time distribution system into doing two different time scales, and simply distribute their calendar days as one of several polynomial offsets from their underlying precision time and frequency distribution system.
Only if it drifts. Our planet's UT1 drifts with respect to atomic time not because of measurement errors, but because of internal exchanges of angular momentum, predominately due to fluid motions in the liquid outer core. Mars has a fluid outer core; whether or not it actually undergoes significant long period drifts in planetary spin rate remains to be seen. Hopefully, this will be answered by the Insight lander set to go to Mars at the next launch window. (Note - Like Viking and Pathfinder, Insight will not have a DSAC, but will use round trip range and Doppler to measure Mars rotation rate with respect to terrestrial Atomic Time.) Marshall
-- Steve Allen <sla@ucolick.org> WGS-84 (GPS) UCO/Lick Observatory--ISB 260 Natural Sciences II, Room 165 Lat +36.99855 1156 High Street Voice: +1 831 459 3046 Lng -122.06015 Santa Cruz, CA 95064 http://www.ucolick.org/~sla/ Hgt +250 m