[LEAPSECS] ITU-R SG7 to consider UTC on October 4

[Steve Allen]

On Thu 2010-08-05T14:55:25 -0600, M. Warner Losh hath writ:

> in the UK there's not a clear distinction between GMT and UTC and

> often (but not always?) the terms are used interchangeably.


Listen to the BBC.  Many of the readers will announce that it's
"X o'clock GMT" when that means "X o'clock British Summer Time".


> Evidently, the 0 meridian (as defined by

> GPS) don't fall precisely where it used to, so the observatory that

> made the measurements is a little off.


The RGO was moved from Greenwich to Herstmonceux in 1957, and that
included the operational meridian circle.  From that date there has
been no device capable of authoritatively defining the meaning of GMT
as specified by the IMC.  In the interim there were many changes, the
first ones described in the BIH Annual Report for 1968

http://www.ucolick.org/~sla/leapsecs/BIHAR1968.JPG

This table refers to 3 changes of conventions which caused global
discontinuities in latitude, longitude, and/or UT1.  (The longitudes
changed again on 1984-01-01 with the switch to FK5 that reset the
prime meridian to match the satellite Doppler ranging which was
already being performed at the time of this publication, but that
switch demanded continuity of UT1, as did the subsequent changes of
1997-02-27 and 2003-01-01.)

Nobody can say what GMT means in a manner that requires anyone
else to agree.

--
Steve Allen                 <sla at ucolick.org>                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