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    Re: Modifacation to 2102-D
    From: Gary LaPook
    Date: 2009 Aug 13, 00:33 +0200
    I get it. You simply added one more disk marked clockwise with 360º. You then added markings to this scale marking out hours every 15º starting at 180 and also going clockwise. You then added one more set of markings for the first day of each month marking the GHA Aries for zero hours GMT on the first of the month. You then use a standard 2102-D with this extra scale. Your manipulation of this set up allows you to compute mechanically the LHA of Aries for the time of observation. Pretty slick.

    But (of course) I like my modifications better although they would take longer to make since they allow you to set the 2102-D for the observation without knowing the time in advance, in fact, it tells you the time of sunset and nautical twilight. as it is automatically set up to indicate the positions of the stars for the observation period.

    see:  http://www.fer3.com/arc/m2.aspx?i=107982&y=200904


    byronink@netzero.com wrote:
    9:25 AM
    The set up as shown on my Astronomer. Hope you can read the Base Disk?
    You DR. or yard at home. 45N,71W Feb 4 observer GMT 20:56.
    There are 3 disk involved 1 Base disk(carries all needed information,)2 horizon Disk, 3 star disk.
    Place the horizon disk on the base disk and rotate it to 71w.
    Your sky and horizon is set up to your closest LAT & LONG.
    Find &Read the GMT at Feb 4= 20:56 off the base disk.  You want to observe at GMT 8:38. The outer rim is GMT only.
    Add 20:56 and 8:38 together= 29:34 subtract 24:hours  leaving 5:34.
    Place the star disk on the disk and rotate Aries to GMT 5:34. Done! your sky is set-up.  It that easy and quick. Find the month & day, read the GMT add the Gmt that you want to observe, set Aries to that time.
    Note the 20:54 is equal to the start (GMT 00 of the day for Feb 4.
    Now you can advance time from 5:34 as desired 5:34 is really the observe time of 8:38. You can advance to any sky occurrence ,(rise set what ever you desire ) read the time off the base disk at Aries and subtract the Month and day time to get the GMT. Each degree equals 1 day and 4 minutes of time.
    This simple use, was made to educate and attract the young.
    The Astronomer was mad to teach Celestial Navigation.
    The instructor if he looks close will see every item of his course of instruction.
    Linked File: http://www.fer3.com/arc/imgx/f1-byceldisk.jpg
    NavList message boards: www.fer3.com/arc
    Or post by email to: NavList@fer3.com
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