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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. 

   

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