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    Re: British Summer Time versus GMT
    From: Brad Morris
    Date: 2013 Dec 12, 22:23 -0500

    Hello Debra

    The Nautical Almanac is expressed with UTC time and date as the independent variable.  GMT has long ago been discarded in favor of UTC, but the concept is the same.  Further, the Nautical Almanac does not account for the shift in hours related to summer/winter daylight savings time.

    In practice, you will find the number of timezones before/after the zone at 0 degrees longitude.  You will then adjust the number of timezones by the daylight savings time shift of one.  Then using this number and the current time in your zone, determine the UTC time in the zone at 0 degrees longitude, upon which the almanac is centered and based.

    An example will clarify this for you.  I will use my timezone on the eastern seaboard of the US. Based upon your email address of wombat roo, I'll guess you are in Australia. Using standard time, I am 5 timezones behind UTC on any given date.  So if its 10AM at Greenwich UK, then its 5AM in NYC.  If I want to know my UTC time, just add 5 hours.  But hang on, if its the summer and we are in daylight savings time, my timezones shift by 1.  Therefore, during daylight savings time, to get UTC I add 4 hours. 

    Perth appears to be 8 timezones AHEAD of UTC.  When its 11AM in Perth, subtract 8 to get 3AM UTC.  Unfortunately, I do not know if that's standard or daylight savings.  I'm sure if you help us with your location, we can help you with the determination of the time zones!

    Brad

    On Dec 12, 2013 8:24 PM, "Debra Hillman" <wombatroo@hotmail.com> wrote:

    Does  GMT  change  to british summertime  to be able to have the correct time for using a nautical almanac?
     
    > From: FrankReed{at}HistoricalAtlas.com
    > To: wombatroo{at}hotmail.com
    > Date: Sun, 8 Dec 2013 14:48:47 -0800
    > Subject: [NavList] Radio-quiet oceans and emergency navigation
    >
    > I found a message from one of the earlier incarnations of NavList dating back to December 1995 (on lunars) which I've posted in January 1996 in the main message boards. Here are the messages from that year:
    > http://www.fer3.com/arc/sort2.aspx?y=1996&sort=du.
    > That old message plus my recent ten-year anniversary on here have got me thinking about the long-term changes in the status of traditional navigation including some that are maybe a little surprising.
    >
    > We've often discussed radio direction-finding as a method of emergency navigation. But radio is disappearing as fast as the Internet advances. Broadcast radio is rapidly disappearing in the frequency bands most useful for direction-finding. There are fewer and fewer high-power, long-range AM stations around the world, except in major cities and along the highways that lead to them. Suppose, for example, that you were making that trip I suggested for "spoofing celestial" back in August. You're sailing from Hawaii to Tahiti. How many AM stations could you actually pick up approaching the Marquesas and then Tahiti if you decided to try this sort of emergency navigation? Is it feasible anymore away from large cities? Are the oceans going radio-quiet?
    >
    > -FER
    >
    > ----------------------------------------------------------------
    > NavList message boards and member settings: www.fer3.com/NavList
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    > : http://fer3.com/arc/m2.aspx?i=125693
    >
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    >

    : http://fer3.com/arc/m2.aspx?i=125726

       
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