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    Re: hiding stars
    From: Gary LaPook
    Date: 2010 Nov 3, 17:48 -0700

    There is an obvious subtraction error,

    "367D 20.7M. Subtracting West Longitude of 77D 06.6M gives LHA aries of 290D 17.1M"

    should be 290° 14.1'.

    Your GHA Aries is correct for 2248 Z.

    I'm not sure what you meant by:

    "The following illustrates how I figured LHA Aries. Date was 16 October, 2010, I used the current Nautical Almanac, and added 1 hour to the times shown therein."

    and the ZD was + 4. Does this mean that you actually added 3 hours to your clock time or did you add 4 hours or 5 hours? At 77° west longitude the ZD should be +5 while on standard time and + 4 when on daylight savings time.


    Of course, for setting the 2102-D (which does not require a high level of precision) you figured the LHA Aries the hard way going through the unneeded steps of converting your local time to Zulu time and then back by subtracting your longitude. You can simply look up the GHA Aries for your local time, treating it as though it was Zulu time, and then adjust this number by your offset from the central meridian of your time zone which is 60° west for daylight savings time. Doing the computation this way :

    GHA Aries at 1648 Z is 307° 10.8' Your offset is 17° 06.6' (using a 4 hour offset, central meridian of 60°west) which subtracted from the GHA of Aries gives you your LHA Aries of 290° 04.2', close enough for setting the 2102-D. If you are going to take your practice shots from the same location then this offset will stay constant so you could add the slight difference of 9.9' to your computations in the future to get an exact result.

    Also, please do not call the position you determined an "estimated position," it is a "fix," an EP is something different with a lower level of confidence.

    gl


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