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 <[email protected]> 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 _______________________________________________ LEAPSECS mailing list [email protected] http://six.pairlist.net/mailman/listinfo/leapsecs
