[LEAPSECS] Degrees of Accommodating Time Based on Earth Rotation
sla at ucolick.org
Tue Nov 2 13:44:54 EDT 2010
On Tue 2010-11-02T13:30:42 -0400, Finkleman, Dave hath writ:
> We must correlate time as perceived in our analyses
> with the temporal relationships among objects in the universe.
For the sake of operational systems I would phrase this as the
requirement that all precision intercomparisons of time, i.e, the
difference between any two measures of time, need a lookup table in
order to communicate the information.
Thus in POSIX systems we have the zoneinfo file and the leap seconds
file. For the most precise of all systems we have the NIST
publications of the differences between UTC(NIST) and GPS time, the
publications of the same by USNO and every other national metrology
agency, and the BIPM publication Circular T.
For historical purposes this requires archival publications by BIH of
the predecessor of Circular T, the various papers by Stephenson and
Morrison, and the observing logs of various meridian circle instruments.
For civil purposes this includes the records of local and national
legislation and decrees by various authorities.
By which I say that nobody can tell me what time it is, and neither
can I say it. All I can do is to say what my clock reads, to keep
records of how that agrees with other clocks, and to design systems
that tolerate and/or recognize the differences.
Unfortunately many systems have been designed with the presumption that
there is a simple, unique answer to the question "What time is it?"
Steve Allen <sla at ucolick.org> WGS-84 (GPS)
UCO/Lick Observatory Natural Sciences II, Room 165 Lat +36.99855
University of California Voice: +1 831 459 3046 Lng -122.06015
Santa Cruz, CA 95064 http://www.ucolick.org/~sla/ Hgt +250 m
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