NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
What time is it, really?
From: Bill B
Date: 2008 Jul 17, 04:59 -0400
From: Bill B
Date: 2008 Jul 17, 04:59 -0400
A while ago there was a thread on time and the affect of dropping leap seconds on cel nav. I asked a question regarding US Navy computer time lagging behind my GPS time (a Garmin 76). The answer passed my common-sense test--server/router lag. Recently I obtained a clock that polls the Colorado, USA broadcast time signal. (Radio Shack, so perhaps not the optimal atomic-based timepiece.) My understanding, the clock should give me UTC (factoring in the time lag of a broadcast traveling at 186,000 miles per second). It seems to to run nominally a half second faster than my GPS (within minutes after the clock has polled the Colorado signal and reset). If I understand correctly, the Nautical Almanac is based on "UT", which Dutton's claims is UT1. This may differ from UTC. Searching the web, the articles on GPS time versus UTC are confusing to me (perhaps the date of the articles are part of the problem.) I am informed: * GPS time will always lag behind UTC. * GPS time will always be ahead of UTC. * GPS satellite clocks do factor in leap seconds so can run 19 seconds or more behind UTC. * GPS time is "steered" to approximate UTC. (Meaning?) Dutton's also provided two URL's for UTC/UT1 corrections (DUT1) which proved to be dead ends. I finally found a March posting with a correction factor of -0.4 seconds, which seems to sync up with my observations. My questions: Does anyone know of a URL for up-to-date UTC/UT1 corrections (DUT1)? How does GPS time relate to UTC or UT1? Is the relationship somewhat dependent on the make/model/age/firmware of the GPS unit? Can a person with two watches (clocks) ever know what time it is?Thanks Bill B. --~--~---------~--~----~------------~-------~--~----~ Navigation List archive: www.fer3.com/arc To post, email NavList@fer3.com To , email NavList-@fer3.com -~----------~----~----~----~------~----~------~--~---