[LEAPSECS] Cheating means more planning, not less
sla at ucolick.org
Sat Dec 27 21:40:22 EST 2008
On Sat 2008-12-27T19:22:00 -0700, M. Warner Losh hath writ:
> Correct. However, the die was cast on this in 1958 when the second
> was defined in terms of atomic behavior. At that point, the game was
> up, since the basic unit of time was decoupled from the day. We
> transitioned from having rubber seconds, to having rubber days. I
> suppose we could push this back further when the second was defined in
> terms of the mean solar day in 1900, since that changed a division of
> a day, to the day being so many seconds. A subtle difference that
> appears to have been lost on the people taking this first step, at
> least at the time.
The cesium chronometer was created in the UK 1955, and within only a
few months Markowitz of the USNO was rushing to start comparing it
with the lunar observations of the dual rate moon camera, and the
results of that intercomparison were reported before the experiment
was really over.
Markowitz in his role as chair of IAU 31 was in a tremendous race to
see that the cesium would be calibrated with ephemeris time. There
was barely enough time to reduce the observations they had made let
alone to comprehend their meaning for either the short term or long
term. During that experiment they noted that the rate of earth
rotation was in a particularly fast phase of variation.
I believe there is a memoir by Markowitz where he indicated the
pressure he felt he was under to get an astronomically based
definition before the physicists simply chose a number. I haven't yet
seen it, and I can't cite it off the top of my head.
I have seen no references which indicate that anyone had then
recognized that ephemeris time was roughly in agreement with
the mean solar day of 1820. There are a number of places where
astronomers incorrectly stated that ephemeris time matched the
mean solar day of 1900.
Steve Allen <sla at ucolick.org> WGS-84 (GPS)
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