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    Re: Beginner Meridian Passage Question
    From: Michael Dorl
    Date: 2004 Sep 9, 08:39 -0500

    Somebody gave me a book called 'Latitude Hooks and Azimuth Rings' by Dennis Fischer publisher International
    Marine.  In it he describes several old instruments and gives directions for making them.  Included is a device
    called a Nocturnal.  The Nocturnal came in many forms, the one Fischer describes is useful for...

      determining local time by observing the position of Ursa Major (or Minor) with respect to Polaris

      determining the correction to be applied to the height of Polaris to determine latitude again by
      observing the position of Ursa Major (or Minor) with respect to Polaris.

      calculating the position of the moon given the local time, date, and day of lunar month.  Useful for predicting
      local high and low tides times.  EG. When should I leave port on a given date to sail on the falling

    I made one and its actually quite good at determining local time, it's easy to come within 10 minutes.  The
    Polaris correction is more than good enough to get you within 5 minutes of angle.

    see http://brunelleschi.imss.fi.it/genscheda.asp?appl=SIM&xsl=multimed&lingua=ENG&chiave=500044

    If you want the book see http://www.celestaire.com/catalog/products/5722.html or many other sources.
    Search for Latitude Hooks and Azimuth Rings Dennis Fischer for other sources.

    I'd think a Nocturnal or a sketch of the position of Ursa Major and Ursa Minor at Polaris meridian crossing would
    be a useful life boat adjunct.
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