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    Re: Ice on the ocean
    From: Magnus Sjoquist
    Date: 2011 Feb 8, 00:32 -0800

    Rolland:
    It is not necessary to invest good money in an artificial horizon. Take a tin, cup, bowl or whatever and fill it with water. Measure angle between true sun and the refected image. In principle, the measured angle will be the double angle, compared to what you would get measuring angle sun - horizon.
    1. Correct the double angle for instrumental error.
    2. Divide by two.
    3. Forget the dip (no dip of horizon in the tin).
    4. Apply refraction (same correction that you normally would apply to a star or planet observation) - found in Nautical Almanac.
    5. After these minor calculations you have the true altitude.

    Note: If you make the observation so that the "two" suns overlap each other (and not outer edges as you probably would taking a lunar) there is no correction for semidiameter (which explains why you can use the star altitude correction table instead of the sun ditto).
    Before mercury became very illegal to use it was used instead of water. If you have problems with outdoor temperatures (also the water in the tin could freeze) i reckon you could use oil of some kind (or water mixed with some antifreeze chemical). /Magnus

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