NavList:

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Von: "P H" <pmh099@yahoo.com>
Gesendet: 18.01.2011 20:32:31
An: NavList@fer3.com
Betreff: [NavList] Re: azimuth of polar star

From what I would guess (and also from reading the site with my rather limited knowledge of German) it is intended to increase the accuracy of determining true north from looking at the direction of Polaris.  This could perhaps be used for checking the gyroscopes.

As for the sensitivity of the computed azimuth to inaccuracies in input data, I did the following calculation:

2011 Jan 18, UT = 00:00:00
N 40.0,  W 120.0:   Az = 37.4'
N 40.5,  W 120.0:   Az = 37.6'
N 40.0,  W 121.0:   Az = 38.0'

Five minutes later from the same reference position:
N 40.0,  W 120.0:   Az = 36.5'

And now with all three "errors" present:
2011 Jan 18, UT = 00:05:00
N 40.5,  W 121.0:   Az = 37.5'

It appears that the (in)sensitivity of azimuth to input data is greatly aided by the star's closeness to the Pole.  After all, if it were exactly at the Pole, we'd have Az=0 always, regardless of time and location.  It very well may be (I am not sure) that a mechanical computer (such as a slide rule) could match the requisite 1' sensitivity - that is a separate question, which other NavList members are in a better position to answer.


Peter Hakel

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From: Ronald van Riet <ronald@van-riet.nl>
To: NavList@fer3.com
Sent: Tue, January 18, 2011 8:41:10 AM
Subject: [NavList] azimuth of polar star

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?

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...

thanks

Ronald
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