NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Tai, Gps, Utc.
From: Jim Easton
Date: 1997 May 21, 13:40 EDT
From: Jim Easton
Date: 1997 May 21, 13:40 EDT
Found the following: Date: Mon, 19 May 97 21:59:54 -0700 From: William Lewis <wiml@XXX.XXX> Subject: Re: ~2K (Ladkin, RISKS-19.16) Actually, GPS uses a measurement of time that has the same definition of a second as UTC and TAI, but is offset a constant 19 seconds from TAI. This was the same as UTC in 1980 (the GPS epoch), but leap seconds have increased UTC's offset from TAI to 30 seconds (soon to be 31) while GPS time has remained unaffected. Anyone trying to reconcile GPS time with local civil time (based indirectly on UTC) has to take this into account. (Personally, I think computers should keep time in TAI and have a table of leap seconds along with the time zones and other human-generated time cruft.) The GPS clocks do take numerous relativistic effects into account; presumably TAI and UTC are canonically measured at some particular location, with its particular dilations and whatnot. Astronomers have time scales such as TDB (Barycentric Dynamic Time) which account for relativistic effects on the Solar-system scale, and have ways to deal with the fact that simultaneity isn't a well defined concept in the first place. Jim Easton 4364 Bonita Rd., No. 166 Bonita, CA 91902-1421 Tel: 619-548-0138 Fax: 619-470-8616 =-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=--=-= =-= TO UNSUBSCRIBE, send this message to majordomo@XXX.XXX: =-= =-= navigation =-= =-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=--=-=
