On Thu 2008-02-14T14:07:52 +0000, Tony Finch hath writ: > How does the mean solar day relate to ephemeris time?
Again, the interval when the worst chaos reigned as people tried to figure out how to answer that question is covered in this 1966 document by the geodesist trying to explain it all for NASA. http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19660020453_1966020453.pdf The scholarly record in the refereed journals, the long sequence of publications by the BIH, and references in the works by Guinot point to a treasure trove of material by Stoyko that must be in the BIPM and/or Paris Observatory from the interval of history when this was being grokked. For a shorter version see Seidelmann's writeup in Explanatory Supplement to the Astronomical Almanac, University Science Books, 1992 http://www.amazon.com/Explanatory-Supplement-Astronomical-Almanac-Seidelmann/dp/0935702687/ For another short version see the Metrologia paper by Nelson et al. The leap second: its history and possible future, v38, #6, pp509-529, 2001 I think there are aboutt three copies out there on the web. For another insider's view see the book by Audoin & Guinot The Measurement of Time: Time, Frequency and the Atomic Clock Cambridge, 2001 http://www.amazon.com/Measurement-Time-Claude-Audoin/dp/0521800803/ For the long view see all the annual publications of the BIH and the USNO regarding their work with radio signal time sync. Also the triennial publications of the IAU general assemblies with focus on the output from commission 31, especially the proceedings from the late 1950s through early 1970s. For those with access to material not yet available try the book being written by McCarthy and Seidelmann for publication by Wiley. I suspect it will be very good. If anyone knows of any memoirs of this sort penned by Markowitz then I would not be alone in really wanting to learn about them. The words from the 1964-08-28 meeting of IAU commission 31 have remained true over more than 40 years: La distinction entre epoque et intervalle de temps n'est pas claire pour tous. There is a distinction. POSIX zoneinfo and its equivalents in other precison+civil time systems already have the mechanisms to let the distinction be clear. They can handle both a monotonic interval and a conversion to and from various epochs that corresponds to externally mandated standards. The question is whether or not we want to insist on broad cognition of that distinction, or whether we'll dumb down reality for the sake of simplicity. -- 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 LEAPSECS@leapsecond.com http://six.pairlist.net/mailman/listinfo/leapsecs