NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
From: Lu Abel
Date: 2011 Mar 18, 17:08 -0700
Time zone designators (eg, Time Zone "U") are used principally by the military. Ships at sea also usually keep "local" time in accordance with their longitude. At sea, time "zones" are simply defined as +/-7.5 degrees from a central meridian which is an exact multiple of 15 degrees.
Totally separate from that is the concept of Civil Time -- the time kept ashore, which may be influenced by both keeping of daylight savings time and zone boundaries (for example, Indiana keeps Eastern time (except for its northwest corner which, because of its proximity to Chicago, keeps Central time). Terre Haute is only about 2.5 degrees of longitude shy of Lo 90 W, the central meridian for Central Time, yet it keeps Eastern time. Civil time in some countries is not even an exact number of hours off from Greenwich Time. India, for example, is 5-1/2 hours ahead of Greenwich time -- and Nepal is 5-3/4 hours ahead!
When keeping civil time, time zone designators (eg, time zone "U") are not relevant. What is relevant, though, is our Zone Designator. So, yeah, we on the West Coast of the US just slipped from ZD +8 to ZD +7. But unless we're at sea keeping ship's time, the "U" designator is not relevant.
Lu Abel
From: Gary LaPook <glapook@pacbell.net>
To: NavList@fer3.com
Sent: Fri, March 18, 2011 11:56:02 AM
Subject: [NavList] Re: NavList zone decriptions
I also have a question concerning time zone naming conventions. I live in California which is the Pacific Time Zone. This is also the "U" time zone. During part of the year we keep "Pacific Standard Time" which has zone description + 8 so we add 8 hours to our clock time to find GMT. During the summer in the Pacific Time Zone we keep "Pacific Daylight Savings Time" which has a Z.D. of + 7 so we add 7 hours to convert our clock time to GMT. My question is what happens to the "U" designation when we go on daylight savings time? Do we then keep time with a Z.D. of + 7 in the "U" time zone, meaning that the "U" zone is physically fixed to the Pacific Time Zone or to we keep "T" time in California, meaning that the letter designations are fixed to the zone descriptions so that we change letter designation when we change Z.D.?
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