A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
From: David C
Date: 2017 Feb 21, 00:26 -0800
According to Blackburne the ABC tables can be used for more than calculating azimuth. Here are the claimed uses:
- Find azimuth
- Find error in long due to an error in lat when working a time sight.
- Find initial great circle course.
- Find great circle distance
- Find meridian of GC vertex
- Find latitude of GC vetex.
- Find a succession of points on a GC to plot track on a Mercator chart.
- Find the long of the point of tangency of the arc of a GC with the limiting parallel of lat (as in NZ to Cape Horn)
- Windward GC sailing.
- Identify an unknown star.
- Given lat, dec, hour angle find the alt. ...............Use for intercept method???
- Find reduction to the meridian (in conjunction with ex-meridian tables)
- Find hour angle of maximum altitude with A and B tables .............Investigate this?
The calculation of azimuth and the calculation of initial GC course are the only uses I have put the ABC tables to. I have marked two other uses that IMHO deserve further investigation. When working an intercept I determine the azimuth with the ABC tables. If I have interpreted what Blackburne has written correctly then I can also calculate Hc by ABC tables. i.e. the ABC tables and the NA are the only volumes I need for astro. It seems too good to be true. I suspect that the interpolation required and the low precision would make this method impractical except in an emergency.