On Tue 2020-05-05T13:14:44-0600 Brian Inglis hath writ:
On 2020-05-04 19:58, Paul Gilmartin via tz wrote:
On 2020-05-04, at 18:26:22, Andrew Gierth wrote:
(To the best of my knowledge there are no reference clocks available to which one could synchronize in order to use a mean solar time, so your argument seems to me to support this choice.)
Do you mean mean solar time at some arbitrary precise longitude or mean solar time at the Prime Meridian? If the latter, is interpolated UT1 a close enough approximation?: https://www.nist.gov/pml/time-and-frequency-division/time-services/ut1-ntp-t...
No, as the precision of UT1 based on the Earth Rotation Angle is ms a day; UT1R has 62 smoothing terms; UT2 smoothes out seasonal variations; some variation of UT would be required to provide mean solar time at a consistent rate. NIST are still applying radio clock accuracy standards with ~ms precision, where the current norm is ~us from GPS, certainly over local LAN and even over decent remote WAN links.
The UK radio broadcast time signals stopped providing GMT in 1953. Starting then they transmitted Provisional Uniform Time, PUT, which was their own forerunner version of UT2. The US radio broadcast time signals made similar changes around then. The USNO version of uniform time scale had names like N3c. So since the 1950s there has been no real-time source of mean solar time, only quartz and cesium clock time adjusted to follow that.
The older standard is adequate for MS products which require only watch-and-eyeball accuracy, but more systems are needing more accurate time.
Different sources of radio broadcast time signals did not agree to within 1 ms until 1960 when the US and UK began to coordinate their transmissions using cesium. -- 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 https://www.ucolick.org/~sla/ Hgt +250 m