NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: Bubble horizon
From: Robert Eno
Date: 2002 Dec 17, 08:39 -0500
From: Robert Eno
Date: 2002 Dec 17, 08:39 -0500
Happy to respond. I find the results are more accurate if the size of the bubble is slightly larger than the body being observed; in the case of the sun or moon, the diameter of the bubble should be just enough to encircle those bodies. In the case of stars and planets, it is a fine balance. If the bubble is too small, I find that it becomes sluggish and lags, thus the accuracy drops off. It should be lively enough to move freely with the slightest movement of the observer. I am finding it hard to encapsulate this in words. It is one of those things which one must experience first-hand in order to fully grasp the concept. Robert ----- Original Message ----- From: Dr. Geoffrey KolbeTo: Sent: Tuesday, December 17, 2002 3:52 AM Subject: Re: Bubble horizon > Robert Eno wrote: > > >To make a long story short, unless you can adjust the size of the bubble, > >you will experience errors; sometimes gross errors. > > I, and I am sure some others on the list, would be grateful to Robert if he > could make this short story a little longer. Why is the size of the bubble > critical? Is Robert concerned that the damping of the bubble movement is a > function of bubble size, or that the accuracy with which the celestial > object can be centered in the bubble is a function of bubble size, or some > other consideration? > > To answer George Huxtable's question on the sort of accuracy one should > expect from a bubble sextant. I have a Link A-12 aircraft sextant (still > available from Celestaire, last time I looked,) and I would expect an > altitude measurement to be within +/- one minute. I am disappointed if I am > two minutes out and I cannot remember the last time I was more than two > minutes out. > > Geoffrey Kolbe. > > >