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: Jim Hickey
Date: 2007 Nov 27, 11:27 -0800
From: Jim Hickey
Date: 2007 Nov 27, 11:27 -0800
The Davis Mark 3 sextant runs about $35 and would be good for a group of kids to get their hands on. Since there are no optics, it is pretty easy to line up the suns image using an artifical horizon. I blieeve Omar Reis on his web site shows how to make a sextant out of a CD. If I was very careful with the one I had and plotted the angles, I could get a LOP within about 4 minutes. You may also want to consider making an strolabe there are some kits available or you could fabricate one fairly easily. The theory behind a LOP might be a little deep for the age group but they might get more out of the astrolabe. You would also eliminate the horizon issue. Jim On Nov 27, 10:20 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. --~--~---------~--~----~------------~-------~--~----~ To post to this group, send email to NavList@fer3.com To , send email to NavList-@fer3.com -~----------~----~----~----~------~----~------~--~---