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    Re: azimuth of polar star
    From: Gary LaPook
    Date: 2011 Jan 18, 15:25 -0800
    I have to agree with George since there is no need for the azimuth of Polaris to be that precise for celestial navigation. I am attaching the Polaris table from the Air almanac for 2011 (there is similar information in the NA) which gives the azimuth of Polaris to a precision of only 0.1 degree, 6 minutes of arc. At the equator the azimuth varies up to 0.7 degrees from true north and at 70 degrees latitude it varies by 2 degrees.

    I posted back in 2007 information about how the azimuth of Polaris was used for aligning artillery on the "azimuth of fire."

    http://www.fer3.com/arc/m2.aspx?i=103114&y=200708

    http://www.fer3.com/arc/m2.aspx?i=103115&y=200708

    I am attaching the graphs from FM 6-50 used to determine the azimuth of Polaris which is read out in mils (6400 mils = 360 degrees, 1 mil = 3.4 minutes).

    gl

    --- On Tue, 1/18/11, George Huxtable <george{at}hux.me.uk> wrote:

    From: George Huxtable <george{at}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{at}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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