sla at ucolick.org
Thu Apr 29 15:57:07 UTC 2021
On Wed 2021-04-28T23:38:59-0600 Brian Inglis via tz hath writ:
> It also appears that UT1 can be "accurately" and "reliably" determined only
> to orders of milliseconds at any time, presumably why the DUT1 change
> announcements are made in 100ms increments, based on the likely trend.
Note that 1 ms = 0.5 m
A 1 m accuracy for GPS requires less than 2 ms error in UT1.
Reductions of data from the day of a VLBI campaign give UT1 accuracy
around 1 microsecond. That is only available after correlation and
degrades rapidly, but it is essential for the Event Horizon Telescope.
The 100 ms steps in DUT1 were deemed adequate for celestial navigation
and feasible to provide in 1971-02 as detailed in CCIR Report 517.
That report was produced by folks unfamiliar with the magnitude of the
stochastic processes and the limits of the sampling theorem so they
supposed the maximum |UT1-UTC| could be maintained within 0.7 s, and
they wrote that impossible-to-achieve limit into an international
regulatory document as well as the design of radio time signal
> > An alternative would be to use the future predicted values of UT1 to
> > predict leap seconds.
> That's what IERS do: see comment about Silmarillion! ;^>
The Silmarillion is a laudable and detailed construction of a past
that did not happen on this earth. Predicting the future evokes
another plethora of aphorisms.
Steve Allen <sla at 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
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