[LEAPSECS] Java: ThreeTen/JSR-310
sla at ucolick.org
Fri Jan 28 13:34:14 EST 2011
On Fri 2011-01-28T18:03:07 +0000, Stephen Colebourne hath writ:
> JSR-310 addresses the definition of 1970-01-01Z (by defining the
> TAI-UTC gap as fixed at 10 seconds prior to 1972.
This is pointless silliness. This is defining a time scale which did
not exist and presuming that it can be used for something practical.
For any precision purposes TAI and UTC did not exist before
1972-01-01. TAI only got its name in 1971, and the only way to access
it prior to 1972-01-01 was by painstaking tabular lookup of the
offsets of the time signal used for a time stamp.
Until that instant the UTC being broadcast by the Soviet Union (and
other stations) differed from other broadcasts by milliseconds. I can
go over to the library and find the BIH Circular with the exact
number, but it was not small.
Before 1972 the only practically available time scales were nebulously
synchronized versions of UT. Those are measures of earth rotation,
suitable for subdividing the days of the calendar. Presuming that
they are suitable for any other purpose, or defining a general-purpose
scheme to make use of them for precision purposes, is a mistake.
All proleptic time scales are dangerous, for in the absence of a
contemporary authority to define what they were, any one
interpretation is likely to differ from another.
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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