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    Re: Go-To telescope for practice navigational fixes
    From: George Huxtable
    Date: 2010 Mar 19, 17:59 -0000

    That's interesting technology. Tell us something, Jim, about the initial
    setting-up procedure. How is the necessary levelling and North-South
    orientation done? Presumably, a target star or stars will be involved. How
    well is the alignment of the optical axis of the scope to the reference
    direction of the mount controlled? What sort of overall pointing precision
    is achieved?
    
    George.
    contact George Huxtable, at  george@hux.me.uk
    or at +44 1865 820222 (from UK, 01865 820222)
    or at 1 Sandy Lane, Southmoor, Abingdon, Oxon OX13 5HX, UK.
    ----- Original Message -----
    From: "Jim Stephens" 
    To: 
    Sent: Friday, March 19, 2010 3:35 PM
    Subject: [NavList] Go-To telescope for practice navigational fixes
    
    
    I own several GoTo telescope mounts (iOptron), two of them with a built-in
    GPS and the most basic model without one.  For the mount to work you need
    to input a position or have the GPS functionality.  You mount your
    telescope on the unit, run through an initialization procedure and you can
    slew to an object in the control handset's database as well as track.
    These are alt-azimuth -- not equatorial -- mounts, so the on-board computer
    generates tracking rates for both axes continuously. The mount's control
    unit computes coordinate transformations, slews to objects, and generates
    the necessary tracking rates.
    
    You can use these in a manual mode, and in that case you essentially have a
    theodolite.  So you can measure the altitude (it reads out on the
    hand-controller) of a star, mark the time, and you have a star shot!  An
    exercise in circular logic with the GPS, I know, but it's an exercise.  And
    in the case of the non-GPS-equipped model, you can set the thing up, level
    the mount (and attached) telescope properly, turn it on and simply leave it
    in a manual mode.  (You can also do this with the GPS-equipped models, just
    turn them on, leave them in manual control).  In fact any alt-az telescope
    with digital setting circles (DSCs) can probably serve as a very good
    theodolite.  I'll bet a few of the list members have telescopes.  The nice
    thing about using your DSC equipped telescope as a theodolite is that you
    can choose a comfortable eyepiece, whereas with an actual surveyor's
    instrument you may not have much choice.
    
    Another exercise with the GoTo scope: slew to a star and read the altitude
    and time, slew to another, and another, and you have a practice problem for
    sight-reduction.  You can even do this indoors and do simulated slews.  The
    hand controller indicates the star's altitude.
    
    Jim
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