A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
From: Bob Goethe
Date: 2015 Apr 18, 15:27 -0700
>>What is typical best accuracy with mirror or pool of fluid?<<
I have used water in a cereal bowl while sitting on the floor of my living room (hence, breezes rippling the water's surface are non-issues as long as the furnace is not running). This is a pretty controlled environment: I'm sitting on the floor, and can dial in my sights pretty carefully. I get plots within 3 miles all the time; within 1 mile about half the time. I have a Tamaya sextant.
Sometimes the pencil lead runs right across the top of my GPS position on my plotting sheet...but I know that this is indeed random. I am using pub. 249, which gives postions plus-or-minus 0.5 nm. So anything closer than ½ mile is indeed just lucky.
I have used a glass mirror...but found that I was getting fuzzy edges on my reflected sun. There was a primary reflection off the mirrored surface on the back of the glass, plus another reflection off the front side of the glass. The combination of those two reflections translated into what looked like a fuzzy edge.
So even though having my wife walk anywhere on the main floor of the house (or having a vehicle drive past on the road) while I am taking a sight will set up ripples in my cereal-bowl horizon, it is fundamentally better than a regular mirror for me.
I have wondered about the possibility of getting a mirror where the reflective surface is on the FRONT of the glass rather than the back.
I expect that the most skilled sextant users - though probably not the best celestial navigators - are alive today. Having a GPS on your cellphone with which to compare your celestial plots lets you indentify any systematic user errors in sextant use to a level that was simply not feasible a century ago.