NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: Slide Rule Azimuth
From: Bill Noyce
Date: 2009 Jun 1, 14:38 -0400
From: Bill Noyce
Date: 2009 Jun 1, 14:38 -0400
On Sat, May 30, 2009 at 3:16 PM, George Huxtablewrote: > > Gary has pointed out the ambiguity, for azimuths near East and West, which > is the serious drawback to this method of working (more serious, in its way, > that the poor precision at these angles, which Greg did recognise). But he > pointed it out, only to dismiss it, as "not a problem in real life". I > suggest he should think again. This same azimuth formula is used in Ageton's method, where it's especially convenient because COS declination and SIN meridian angle (actually, the logs of their inverses) were already used in computing the altitude. In this application, the ambiguity as to whether the azimuth is just north or just south of due east or west is easy to resolve. In Ageton's method, like the Bygrave method, one intermediate result is the latitude at which a perpendicular from the observed body hits the observer's meridian. If this latitude is north of the observer, then the body's azimuth is to the north; if south, then south. Of course, the problem of precision of the arc-sin of values near 1.0 still remains, but for short intercepts that's not too serious either. -- Bill --~--~---------~--~----~------------~-------~--~----~ Navigation List archive: www.fer3.com/arc To post, email NavList@fer3.com To , email NavList-@fer3.com -~----------~----~----~----~------~----~------~--~---