NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: azimuth of polar star
From: George Huxtable
Date: 2011 Jan 18, 21:06 -0000
From: George Huxtable
Date: 2011 Jan 18, 21:06 -0000
Ronald van Riet asked- "A slide rule (well not quite, but close enough to be called a slide rule) exists that was used to determine the azimuth of the pole star: the P.A.44 (http://www.rechenschieber.org/pa44.html web page in German). Does anyone know of a reason why the azimuth of the polar star is important enough to develop a dedicated slide rule for it?" It seems more relevant to land-based North-users rather than to sea navigators (to whom precise azimuth is out-of-reach because of their unstable footing). Such as land surveyors, mapmakers, those who may wish to align field-guns, backyard astronomers setting up telescope pillars. That sort of application. "Also, they claim that with a half degree of latitude, a full degree of longitude and about five minutes time accuracy, the azimuth could be determined with a 1 minute of arc precision. Could that be a valid claim? It seems a bit too precise with the imprecise inputs..." Yes, it certainly could. As Peter Hakel points out, the azimuth of Polaris is always within a whisker of due North, wherever and whenever it's observed from. What has to be calculated is just a small correction, because the declination of Polaris differs from 90º by just a fraction of a degree. It's easy to deduce that correction to sufficiently high precision, with a slide rule. George contact George Huxtable, at george@hux.me.uk or at +44 1865 820222 (from UK, 01865 820222) or at 1 Sandy Lane, Southmoor, Abingdon, Oxon OX13 5HX, UK.