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    Re: Children's land-locked "Sextant"
    From: David Cortes
    Date: 2007 Nov 28, 08:47 -0800

    Gary:
    
    
    Did I read you right?  I can download HO 229?  At what site or link?
    
    David C.
    
    
    On Nov 28, 3:13 am, glap...---.net wrote:
    > Gary adds:
    >
    > Go to the on line publications link then scroll down and you can also
    > download Ho229 and HO 249.
    >  Here is a link to a site where you can download for free varius
    >  navigational publications including the American Practical Navigator,
    > HO
    >  9, Bowditch. Table 14 is the dip short of the horizon table.http://
    > 164.214.12.145/index/index.html
    > gl
    >
    > On Nov 27, 11:33 pm, "Gary J. LaPook"  wrote:
    >
    >
    >
    > > Gary LaPook wrote:
    >
    > > Here is a link to a site where you can download for free varius
    > > navigational publications including the American Practical Navigator, HO
    > > 9, Bowditch. Table 14 is the dip short of the horizon table.http://164.214.12.145/index/index.html
    > > gl
    >
    > > Rebecca Lowry wrote:
    > > > Hi,
    >
    > > > I'm also in the process of learning.
    >
    > > > Any chance you could send, or email, a couple to me as well?
    >
    > > > thanks,
    > > > Wayne Lowry
    > > > 93915 prairie rd
    > > > Junction city, Oregon 97448
    > > > USA
    >
    > > > Greg Rudzinski  wrote:
    >
    > > >     I suggest demonstrating a polaris observation to your young students
    > > >     using the far shore of a lake as a horizon. Bowditch table 22 will
    > > >     give you the dip correction. A pub. 249 vol. 1. table 6. correction
    > > >     needs to be made (up to 44 minutes of arc). Table 6. requires a local
    > > >     hour angle of Aries entry. I have a homemade pocket table that
    > > >     simplifies some of this. E-mail me a mailing address and I will send
    > > >     you a few.
    >
    > > >     Greg Rudzinski
    > > >     gregrudzin...---.com
    >
    > > >     On Nov 27, 7:20 am, Isonomia wrote:
    > > >     > I'm camping next summer with a load of 11year old kids and wanted to
    > > >     > do some celestrial navigation and plot a position to within
    > > >     > 10-20miles.
    >
    > > >     > Has anyone ever built a simple theodolite type sextant out of basic
    > > >     > DIY material and managed to obtain an accuracy that would allow a
    > > >     > basic position plot and if so how?
    >
    > > >     > In particular I would like to build a form of "sextant" based on
    > > >     > measuring the angle above a horizontal plane of the sun using the
    > > >     > sun's shadow.
    >
    > > >     > I'd welcome comments, suggestions or practical experience on:-
    >
    > > >     > 1. How to create a horizontal plane to within a few minutes
    > > >     accuracy?
    > > >     > 2. How to obtain a good shadow/image, e.g. has anyone tried glass
    > > >     > lenses?
    > > >     > 3. How to measure an angle from the horizontal to the sun's
    > > >     image to a
    > > >     > few minutes?
    >
    > > >     > All contributions greatfully received.
    >
    > > >     > Mike
    >
    > > >     > HISTORY & WHAT I'VE STOPPED CONSIDERING
    >
    > > >     > I started by considering using a sextant with an artificial horizon.
    > > >     > However, whereas it is a skill to find the sun and line it up
    > > >     with the
    > > >     > horizon (sea=go up, sky=go down), trying to line up two images
    > > >     of the
    > > >     > sun is an art. And aligning two images of stars is so difficult I've
    > > >     > only managed a sensible result on 50% of my tries.
    >
    > > >     > My next idea was to use a real artificial horizon, in the shape of a
    > > >     > string set at a distance to give a low arc error. However, after
    > > >     a bit
    > > >     > of calculation regarding the distance (30-100m) and the length
    > > >     of the
    > > >     > string (10-30m), I've realised that any string big enough to see is
    > > >     > going to dip considerably unless it is under such extreme
    > > >     tension that
    > > >     > it is a positive hazard in an open area.
    >
    > > >     > I then considered laser levels - but I'm not looking through a
    > > >     sextant
    > > >     > with potential laser reflections all over place - even if one could
    > > >     > see the laser line in daylight at the distance required.
    > > >     ------------------------------------------------------------------------
    > > >     Be a better sports nut! Let your teams follow you with Yahoo
    > > >     Mobile. Try it now.
    > > >     - Hide quoted text -
    >
    > - Show quoted text -
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