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    Calibrating a Kamal
    From: Bob Goethe
    Date: 2017 Nov 30, 11:58 -0800

    Does anybody know of any two prominent stars in the sky of the northern hemisphere with a separation of 4.0° or 8.0°?


    I have made a kamal, as described in http://bobgoethe.com/Nav/Kamal.html, and am able to match altitudes from my sextant to within 15', where hs is <15°.  But this is with the benefit of carefully using a tape measure to get my string length right, and a computer-graphics program to get the scale on the stick set up.

    If one were trying to calibrate an improvised kamal at sea, and lacked a ruler or other measuring device, he would probably calibrate it (i.e. adjust the string length/degree markers on the stick) by measuring the distance between two stars with a known separation.  The nicest separation to work with would be either 4° or 8°, since one could halve and double whatever scale you draw on the stick to get good precision down to marks that would measure 1/4°.

    • I know that Castor and Pollux are 4.50° apart.  This is good...but I would like get something closer to 4.0° if I could get it.
    • I know that Big Dipper beta (Merak) and delta (Megrez) are 10.05° apart.  This is good, and one could easily extrapolate 5° and 15° on his scale.  But knowing where to place the 3° mark would be a little imprecise.  Doable if nothing better is available.

    I could go out an look with a sextant in my hand, but Cassiopeia - as with most circumpolar stars - is generally washed out by the parking lot lights of the West Edmonton Mall.  So I was hoping somebody knew of a couple of good stars just off the top of his head.



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