In message: <E1EzNgB-0002TX-00_at_grus.atnf.CSIRO.AU>
Mark Calabretta <mcalabre_at_atnf.CSIRO.AU> writes:
: On Wed 2006/01/18 08:17:54 -0000, Francois Meyer wrote
: in a message to: LEAPSECS_at_ROM.USNO.NAVY.MIL
:
: >Maybe it should be, but this is far from being
: >obvious from its current definition.
:
: I agree that the current definitions leave a lot to be desired in terms
: of clarity and rigour - an uncharitable person might even describe the
: extract of ITU-R TF.460-6 cited the other day by Michael Deckers as
: inconsistent. However, you have to consider how UTC is actually used in
: practice and this is what my comments are based on.
:
: >1. UTC and TAI share the same rate, the same
: > origin, the same second. And therefore :
: >
: > UTC - TAI = 0
:
: They both count SI seconds but the question of the origin is a bit
: muddy.
:
: You could argue that there is a fixed 10s offset between UTC and TAI
: because UTC post-1972 (everything I've said about UTC only applies
: post-1972) started with 10 leap seconds, and before 1972 UTC wasn't
: simply a representation of TAI. There's no simple way of fudging
: radixes that I can think of to make them match up, but if this worries
: you then simply think in terms of proleptic UTC (post-1972),
: see
http://en.wikipedia.org/wiki/Proleptic.
UTC (and its predecessors) prior to 1972 did not tick off in SI
seconds. It used a fixed radix like TAI currently does. The amount
of time in UTC seconds varied a little. Here's the table from
ftp://maia.usno.navy.mil/ser7/tai-utc.dat
1961 JAN 1 =JD 2437300.5 TAI-UTC= 1.4228180 S + (MJD - 37300.) X 0.001296 S
1961 AUG 1 =JD 2437512.5 TAI-UTC= 1.3728180 S + (MJD - 37300.) X 0.001296 S
1962 JAN 1 =JD 2437665.5 TAI-UTC= 1.8458580 S + (MJD - 37665.) X 0.0011232S
1963 NOV 1 =JD 2438334.5 TAI-UTC= 1.9458580 S + (MJD - 37665.) X 0.0011232S
1964 JAN 1 =JD 2438395.5 TAI-UTC= 3.2401300 S + (MJD - 38761.) X 0.001296 S
1964 APR 1 =JD 2438486.5 TAI-UTC= 3.3401300 S + (MJD - 38761.) X 0.001296 S
1964 SEP 1 =JD 2438639.5 TAI-UTC= 3.4401300 S + (MJD - 38761.) X 0.001296 S
1965 JAN 1 =JD 2438761.5 TAI-UTC= 3.5401300 S + (MJD - 38761.) X 0.001296 S
1965 MAR 1 =JD 2438820.5 TAI-UTC= 3.6401300 S + (MJD - 38761.) X 0.001296 S
1965 JUL 1 =JD 2438942.5 TAI-UTC= 3.7401300 S + (MJD - 38761.) X 0.001296 S
1965 SEP 1 =JD 2439004.5 TAI-UTC= 3.8401300 S + (MJD - 38761.) X 0.001296 S
1966 JAN 1 =JD 2439126.5 TAI-UTC= 4.3131700 S + (MJD - 39126.) X 0.002592 S
1968 FEB 1 =JD 2439887.5 TAI-UTC= 4.2131700 S + (MJD - 39126.) X 0.002592 S
1972 JAN 1 =JD 2441317.5 TAI-UTC= 10.0 S + (MJD - 41317.) X 0.0 S
1972 JUL 1 =JD 2441499.5 TAI-UTC= 11.0 S + (MJD - 41317.) X 0.0 S
1973 JAN 1 =JD 2441683.5 TAI-UTC= 12.0 S + (MJD - 41317.) X 0.0 S
1974 JAN 1 =JD 2442048.5 TAI-UTC= 13.0 S + (MJD - 41317.) X 0.0 S
1975 JAN 1 =JD 2442413.5 TAI-UTC= 14.0 S + (MJD - 41317.) X 0.0 S
1976 JAN 1 =JD 2442778.5 TAI-UTC= 15.0 S + (MJD - 41317.) X 0.0 S
1977 JAN 1 =JD 2443144.5 TAI-UTC= 16.0 S + (MJD - 41317.) X 0.0 S
1978 JAN 1 =JD 2443509.5 TAI-UTC= 17.0 S + (MJD - 41317.) X 0.0 S
1979 JAN 1 =JD 2443874.5 TAI-UTC= 18.0 S + (MJD - 41317.) X 0.0 S
1980 JAN 1 =JD 2444239.5 TAI-UTC= 19.0 S + (MJD - 41317.) X 0.0 S
1981 JUL 1 =JD 2444786.5 TAI-UTC= 20.0 S + (MJD - 41317.) X 0.0 S
1982 JUL 1 =JD 2445151.5 TAI-UTC= 21.0 S + (MJD - 41317.) X 0.0 S
1983 JUL 1 =JD 2445516.5 TAI-UTC= 22.0 S + (MJD - 41317.) X 0.0 S
1985 JUL 1 =JD 2446247.5 TAI-UTC= 23.0 S + (MJD - 41317.) X 0.0 S
1988 JAN 1 =JD 2447161.5 TAI-UTC= 24.0 S + (MJD - 41317.) X 0.0 S
1990 JAN 1 =JD 2447892.5 TAI-UTC= 25.0 S + (MJD - 41317.) X 0.0 S
1991 JAN 1 =JD 2448257.5 TAI-UTC= 26.0 S + (MJD - 41317.) X 0.0 S
1992 JUL 1 =JD 2448804.5 TAI-UTC= 27.0 S + (MJD - 41317.) X 0.0 S
1993 JUL 1 =JD 2449169.5 TAI-UTC= 28.0 S + (MJD - 41317.) X 0.0 S
1994 JUL 1 =JD 2449534.5 TAI-UTC= 29.0 S + (MJD - 41317.) X 0.0 S
1996 JAN 1 =JD 2450083.5 TAI-UTC= 30.0 S + (MJD - 41317.) X 0.0 S
1997 JUL 1 =JD 2450630.5 TAI-UTC= 31.0 S + (MJD - 41317.) X 0.0 S
1999 JAN 1 =JD 2451179.5 TAI-UTC= 32.0 S + (MJD - 41317.) X 0.0 S
2006 JAN 1 =JD 2453736.5 TAI-UTC= 33.0 S + (MJD - 41317.) X 0.0 S
(or the yet to be updated
http://www.iers.org/MainDisp.csl?pid=95-106)
Here's slides from a presentation that is actually fairly well
balanced:
http://www.ien.it/luc/cesio/itu/mc_carthy.pdf
It has history there as well. There's a nice graph of the above on
page 20.
http://www.ucolick.org/~sla/leapsecs/timescales.html also contains a
nice summary of UTC which is too long to include here but in outline
form is:
UTC during 1960
UTC from 1961 through 1971
UTC in 1963
UTC in 1965
UTC in 1967 (when the name UTC was adopted)
UTC in 1969
UTC in 1970
UTC starting in 1972
UTC in 1973
UTC in 1974
UTC in 1975
UTC on 1977-01-01
Because the rate of TAI was reduced by one part in 1012, the rate of
UTC was reduced by the same amount. Therefore, before this date UTC
seconds were shorter than they currently are.
UTC in 1978
UTC in 1982
UTC in 1986
UTC in 1988
UTC in 1992/1993
UTC from 1995 through 1998
In 1995 a CCTF working group determined that the length of TAI
seconds was longer than the SI second because the clocks contributing
to TAI were not corrected for the effects of blackbody
radiation. Over the next three years the frequency of TAI was steered
to reduce the length of its seconds by about 2 parts in
1014. Therefore the length of UTC seconds was also reduced. This
change is evident as the final kink in the plot of TT(BIPM04).
http://www.ucolick.org/~sla/leapsecs/dutc.html#ttbipm04.png
UTC in 1997
UTC since 1999
UTC in 2002
UTC(k)
UTC in 2007 ?
UTC in 2022 ?
: However, this is not important and really only confuses things further.
: (It's why I couched the original example as a graph of a person's age
: vs UTC rather that TAI vs UTC.)
Agreed. For such a simple topic, this cat is skinned in too many ways.
Warner
Received on Wed Jan 18 2006 - 20:25:03 PST
