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A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: Practice Bubble vs. Professional Bubble
From: Ken Gebhart
Date: 2012 Aug 5, 21:13 -0500
From: Ken Gebhart
Date: 2012 Aug 5, 21:13 -0500
I feel I should say a few words, since it is our product. 1. It is my belief that part of the inaccuracy experienced with the PBH is the slit which allows focus on a star and the bubble simultaneously. I think that if you move your eye slightly, you will actually see a different picture of the bubble. Perhaps a different retinal image. I am thinking of the eye test where you state which stair step the line passes through. I you blink, you will get a different answer. Perhaps some eye expert will comment on this, and correct me if I am wrong. 2. I have personally taken star sights during star time (when there is enough ambient light to see the bubble, but sufficiently dim to see a bright star) in Kansas where there is low light pollution. 3. We call it a "Practice" bubble horizon because of the inherent inaccuracies. Just to give a beginner some numbers to crunch. 4. It's one of the few products we "push", because it lets landlocked people use their sextants more often. Ken On Aug 5, 2012, at 5:30 PM, bill wrote: > On 8/5/2012 6:17 PM, Alan S wrote: >> I have tried the practice bubble horizon without successa, >> possibly my >> fault, the thing seems "tricky" to use and I have yet to get an >> understandable explaination of the bubble correction factor, as >> with how >> to determine it, .... > > It is simply a matter of looking at the difference of Ho and Hc > from a known position (plus/minus IE). > > Under the K.I.S.S. principle, I determine LAN for my location, and > do several observations while the sun's elevation changes very > little. I also preset for Hs. > > In an attempt to minimize centering the bubble errors while > aligning the sun, I had tripod mounted my preset sextant with the > bubble as close to centered as I could see it. Even then results > were plus/minus 2', so accurately seeing bubble placement is a > limiting factor. > > Bill B > > > > >