NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: What time is it?
From: Trevor Kenchington
Date: 2004 Nov 11, 11:29 -0400
From: Trevor Kenchington
Date: 2004 Nov 11, 11:29 -0400
Thank you, Peter. I guess I will check my GPS display against the dial-up time signal from Canada's NRC. If it is tracking UTC, then it presumably will continue to do so. If it is fast by a good number of seconds, I'll abandon the idea of using at a time reference. Trevor Kenchington Peter Smith wrote: > GPS time is the number of seconds since 06-Jan-1980 00:00:00.0 UTC, and is > steered to an accuracy of better than 1 microsecond. It is encoded in the > GPS NAV message as the number of weeks since 06-Jan-1980 and the number of > seconds since the start of the week. As such, it does not include leap > seconds, so a naive reading of GPS time would be fast of UTC today (13 or 14 > seconds, I believe, for the number of leap seconds since 06-Jan-1980). > However, elsewhere in the GPS messages it gives the correction, so receivers > can display UTC or UTC-derived zone time. > > Interestingly, on 22-Aug-1999, the 10-bit week number field wrapped around > from 1023 to 0, causing some early GPS receivers to lose track of the date. > > The US Naval Observatory's GPS page at http://tycho.usno.navy.mil/gps.html > has some info. > > -- Peter > > -- Trevor J. Kenchington PhD Gadus@iStar.ca Gadus Associates, Office(902) 889-9250 R.R.#1, Musquodoboit Harbour, Fax (902) 889-9251 Nova Scotia B0J 2L0, CANADA Home (902) 889-3555 Science Serving the Fisheries http://home.istar.ca/~gadus