On 2015-01-26 20:05, Brooks Harris wrote:
As a practical matter of modern timekeeping the UTC timescale started at
1972-01-01T00:00:00Z (UTC). NTP, POSIX, 1588/PTP and others refer to epochs and
timescales they call "UTC" that occur earlier than 1972-01-01, so this confuses
matters. But those epochs exist on "Gregorian calendar timescale that is
proleptic to the UTC origin", not on the modern UTC timescale proper. We've got
to get past this confusion.
A calendar provides a method for denoting datetime values.
A time scale is a coordinate function within coordinate systems for
physical (astronomical) models that assigns datetime values to each
point in its domain of definition.
Hence a calendar should not be confused with a time scale, even if
the calendar is used exclusively for the notation of the values of a
single time scale (which is not the case for the Gregorian calendar).
Values of the time scale later called UTC by the BIH can be exactly
related to TAI since 1961, see
[hpiers.obspm.fr/iers/bul/bulc/UTC-TAI.history].
Steve Allen's Time Scales page points out -
Time Scales
http://www.ucolick.org/~sla/leapsecs/timescales.html
"Nothing resembling the name UTC was used prior to 1960, so any claim that UTC
can be used before then is inappropriate. The name UTC did not appear in any
official context until 1974, so any claim that UTC was used prior to 1974 is
almost certainly a reinterpretation of history which does not correspond to
anything in contemporary documents."
The history is tangled, but none of it matters except to historians.
I think that "1974" is just a typo for "1964"; I do not see any error
in the history.
Michael Deckers.
_______________________________________________
LEAPSECS mailing list
LEAPSECS@leapsecond.com
https://pairlist6.pair.net/mailman/listinfo/leapsecs
