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    Re: ZT vs LMT.
    From: UNK
    Date: 2000 Dec 07, 9:01 AM

    Dave Weilacher [mailto:daveweilacher@attglobal.net] asked:
    > Is it appropriate to use Local Mean Time as being
    > synonymus with Zone Time?
    > If you take a test that says "At 1945 hours,
    > after passing Catalina Island and establishing an
    > evening star fix..."
    > then
    > The next statement reads "All times on this test
    > are either LMT or UT"
    > What kind of time would you take 1945 hours to be?
    Some people use "local" and "zone" interchangeably, as the author of your
    test appears to have done. However I think strict usage would have it that
    "local" refers to the observer's meridian, while "zone" refers to the
    central meridian for the time zone in use.
    For example, the longitude of Catalina Island is about 118d 30'W. That puts
    you in the time zone centered on 120dW. So, your Zone Time (ZT) is the same
    as Local Mean Time (LMT) at 120dW, which is 6 minutes slow of your LMT (1.5d
    @ 4 minutes per degree). Your ZT is 8 hours slow of UCT/GMT, so: 1945UCT =
    1145ZT = 1151LMT.
    ...but then, taking tests is as much about figuring out what the test-writer
    wants as giving the "right" answer.  Since it's unlikely that you'd be
    taking a star sight at 1145ZT, and almanacs are (these days) oriented to
    standard meridians, I'm sure the author of the test means local=zone time
    (but I'd have a nit to pick with him if we ever met).
     -- Peter

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