NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: Children's land-locked "Sextant"
From: Gary LaPook
Date: 2007 Nov 27, 23:45 -0800
From: Gary LaPook
Date: 2007 Nov 27, 23:45 -0800
Gary LaPook writes:
Attached are table 14 from Bowditch and the "Q" Polaris correction form H.O. 249 for epoch 2010.
Rebecca Lowry wrote:
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Attached are table 14 from Bowditch and the "Q" Polaris correction form H.O. 249 for epoch 2010.
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 Lowry93915 prairie rdJunction city, Oregon 97448
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
gregrudzinski@yahoo.com
On Nov 27, 7:20 am, Isonomiawrote:
> 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.
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To post to this group, send email to NavList@fer3.com
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