On Sat 2014-01-11T18:49:58 +0000, Michael Spacefalcon hath writ: > But does this ``Zulu'' mean GMT (a natural phenomenon > whose meaning is independent of human whim)
If only it were so, but looking back at the 1884 International Meridian Conference it appears that the reason Simon Newcomb vanished from the meetings was that he agreed when Janssen said it wasn't as simple as that. "A circle has no end" so somehow there must be a human convention for where the "point de depart", the origin, will be. During WW2 when the Airy transit at Greenwich was not in operation the BIH "Heure Definitive" continued to exist via the other observatories. The final Airy observation was 1954-03-30. By 1956 the UK transit astronomers then moved to Herstmonceux noted that the current offset of UT from GMT was small, and admitted they would not even try to establish the exact offset from Greenwich http://adsabs.harvard.edu/full/1957Obs....77...31A It was far too late in 1971 when their successors again wrote about it http://adsabs.harvard.edu/abs/1971Obs....91..155O basically saying "We did what?" because by then the DOPPLER satellite tracking had begun to supersede optical transit measures. The BIH change in weighting from meridian transit observations to satellite, lunar, and VLBI is evident in these 1984 plots from Martine Feissel: http://www.ucolick.org/~sla/leapsecs/MFatt2.pdf Hiding in those charts is the shift of all terrestrial longitudes from their nonrelativistic Greenwich-based local values to their relativistic geocentric global values. -- Steve Allen <s...@ucolick.org> WGS-84 (GPS) UCO/Lick Observatory--ISB Natural Sciences II, Room 165 Lat +36.99855 1156 High Street 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
