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    Re: Time zone confusion
    From: John Huth
    Date: 2011 Oct 23, 11:16 -0400
    John B.- 

    Yes, I agree that time zones are confusing, and constantly shifting.   As many have pointed out on the list, the timezone issues are mainly centered on commerce or political needs, although the 'intent' is presumably to place the sun roughly overhead at local noon.  

    I'm giving my students an exercise this coming week to take a set of sights of the sun and use the equal altitude method to get longitude (it's a basic course, so I use very simple methods).   One of the bigger confusions they have is the step of going to UTC from our eastern daylight time - because I have to explain the nature of the shift, and even the distinction between EDT and EST.  That's probably the most difficult aspect of the entire exercise.   

    One problem I have is that some of my experimental group is located in Geneva, Switzerland.   The shift from daylight to standard time usually differs between Europe and the US by about a week, so we go from a 6 hour time difference to a 5 hour time difference, and our video conferences all get confused, as do phone calls and such.

    John H. 

    On Sun, Oct 23, 2011 at 11:03 AM, John Brown <jdb0302@yahoo.co.uk> wrote:

    I have recently seen several maps showing the world divided into time zones, but the zone labels are inconsistent, with either negative or positive signs used for the same hemisphere.

    Of course, it is not difficult to see how to get UT from ZT and vice-versa, but a simple reference to, say ZT-6, can refer to a time/location in easterly or westerly longitude, depending upon which map one prefers. This is a bit like the common confusion between the sign of an error and its correction.

    It seems logical to use cartesian labelling with westerly time zones as negative, but others disagree. Is there an internationally recognised convention on this? Consulting my usual references is not much help.

    When I was at sea we took no notice of "official" zone time and just adjusted the ship's clocks as necessary to locate lunchtime somewhere in the middle of the day.

    Regards to all
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