NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: AN5954 bubble octant by Bausch and Lomb
From: Alexandre Eremenko
Date: 2012 May 5, 10:31 -0400
From: Alexandre Eremenko
Date: 2012 May 5, 10:31 -0400
Gary, This time it is the right sextant, thanks. (I have not figured out yet how can one search and find anything in the list files database:-) Unfortunately the description is too brief, and some parts of it are not clear. For example, the sentence that "the interval between two series must be approximately 6 seconds". During these 6 seconds you are expected to: a) read and record the reading, (which involves "rotating the drum until the median index is under the index line"), b) reset the scales c) find the star again, and align it with the bubble All these steps they recommend to do in 6 seconds:-) Seems unrealistic to me. The details are still not clear, but apparently they assume that when you shoot VERY quickly (once every 6 seconds), the change of the altitude during the time of observation (90 seconds) can be neglected. In fact, this change can be as large as 22', but under normal conditions (lattitude not too small) it is less. Anyway, they are apparently assuming that the effects of acceleration of the airplane are larger than the effect from the change of altitude in 90 seconds. Moreover, they recommend to use the average time of the beginning and the end of two observations. For one observation, the time can be 45 sec off the actual moment of the selected shot. So it looks like they are aiming at roughly 10'-15' accuracy under the best conditions. Alex.