NavList:

From: George Huxtable <george@hux.me.uk>
Subject: [NavList] Re: azimuth of polar star
To: NavList@fer3.com
Date: Tuesday, January 18, 2011, 1:06 PM

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.