A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
From: David Pike
Date: 2020 May 29, 00:47 -0700
I have some questions regarding the feasibility of celestial azimuth only fixes:
1. Assuming you’re looking to place yourself within 3nm of your true position, what sort of bearing accuracy do you need from bearings of stars who’s altitudes lie between 20 and 80 degrees?
2. Would using the I in 60 rule from the sub-stellar point provided a rough estimate of the accuracy required?
3. Knowing the answer to Q1, and not knowing your starting position, what sort of equipment would you need to find where north is and to measure bearings to the required accuracy?
4. Guessing such equipment will be expensive, can you afford to measure the bearings simultaneously knowing the likely price of two sets of gear?
5. You might try a sandwich fix, but even then, there’s another problem. Even with two 5” theodolites, unlike when you’re taking a bearing on a fixed object, how do you follow a star or planet which might be moving across a 20x theodolite eyepiece at up to 15” of arc per second of time?
6. One method might be to set the theodolite graticule ahead of the star and note the time when the star crosses the graticule. However, this would mean transferring an iso-azimuthal line to obtain the fix. Do we know how to transfer an iso-azimuthal line with respect to time? Can you just transfer an iso-azimuthal line or the stars sub-stellar point westwards like you might transfer an altitude position line or assumed position westwards?
7. In fact, if the equipment your using means you must be stationary, do the bearings need to be taken simultaneously? Why not plot each iso-azimuthal line at the time the bearing was taken? DaveP