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Re: Time zone confusion
From: John Huth
Date: 2011 Oct 25, 13:45 -0400

What do you mean by "ahead" and "behind"?

My zone, currently is "Eastern Daylight Time" - which is listed at UTC - 4. I consider that "behind" UTC, as I have my noon 4 hours later than UTC, but the -4 means that, in order to find my time, I subtract 4 from UTC.

Perhaps the distinction between 1 and 3 is simply that in one case, (1) you seek UTC (so I would add 4 hours to my watch time to get UTC to, say, assess the meridian passage of the sun). In the other case (3), you know UTC, but seek your local timezone, to, say, set your watch, in which case you subtract 4 hours to get your local time. I don't know, but this would make sense to me.

On Tue, Oct 25, 2011 at 1:39 PM, Paul Werner <paul.werner@comhem.se> wrote:

There are, according to the clear explanation in the booklet RYA Astro Navigation by Tim Bartlett, at least three different conventions.
1) The conventional nautical system
Zones ahead of UT are designated as negative.
Zones behind UT are designated as positive.
2) The military system.
UT is designated Z.
Zones ahead of UT are designated from A to M (omitting J).
Zones behind UT are designated from N to Y.
3) The International Standards Organisation.
Zones ahead of UT are designated as positive.
Zones behind UT are designated as negative.
Remark 1)
I know who uses 1) and 2) but who uses 3)? Astronomers?
Remark 2)
Some years ago I had problems understanding the equation of time in old Astro Textbooks until I discovered that Brits and Yankees used opposite plus and minus designations. Nowadays they don't.

Remark 3)
I was tempted just to send a scan of the relevant page in Tim Bartlett's book to the list. Would that have been correct or would I have been stopped next time I tried to go to Britain and put in jail violating some publishing law?

Paul Werner
N59 E18

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