On Wed 2005-08-17T16:45:51 -0700, Rob Seaman hath writ: > I suspect that we are all agreed that a single civil time standard > should exist. The question of multiplicity is one of drawing narrow > distinctions. Many people use devices and systems that rely on non- > UTC time scales, for instance, GPS receivers. Is GPS a second civil > time standard already?
To answer other than one for a civil time standard in the vicinity of earth would be to set the clock back to where it was before the 1884 International Meridian Conference. Some of the point of that conference was to produce a convention for syncronizing human activity on the (then relatively new) trans-oceanic telegraphic cables. > >III) Locale > > A) restricted to Earth [projects or users, not necessarily > >hardware] > > B) other than Earth [e.g., Martian rovers] > > B) Solar system scope > > C) truly Universal > > Personally, I think each planet is likely to require a separate > standard. The spacetime metric adopted by the IAU does not have enough terms in it to generalize to a solar-system wide coordinate system with full precision of current atomic clocks in the vicinity of rotating, gravitating bodies. In a rough sense the metric was designed to permit the definition of a self-consistent coordinate frame out to around twice the geostationary radius. In the broader sense, even a solar-system barycentric coordinate frame is suspect at the level measurable by current atomic clocks, and that is part of the motivation for the various international scientific unions recommending the establishement of a pulsar-based time scale. In a still broader sense, there is no meaning for a universal coordinate time scale. Every observer experiences a proper time peculiar to the local environment. For the foreseeable future, each planet will have its own coordinate time scale. -- Steve Allen <[EMAIL PROTECTED]> WGS-84 (GPS) UCO/Lick Observatory Natural Sciences II, Room 165 Lat +36.99858 University of California Voice: +1 831 459 3046 Lng -122.06014 Santa Cruz, CA 95064 http://www.ucolick.org/~sla/ Hgt +250 m