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    Re: Harry Pidgeon Celestial - Dealing with Seasickness
    From: Frank Reed
    Date: 2013 Nov 15, 11:17 -0800

    In you earlier post, you wrote:
    "How was Mr. Pigeon able to get his fix from a single observation ? Or is the timing of LAN really two observations in one ?"

    Yes. Certainly. A LAN sight consists of at least two attempts to measure the Sun's altitude, and usually more. You measure the Sun's altitude AND you wait for the rate of change of the altitude to be as near to zero as possible. Of course, there are a few other details. A LAN sight (for LATITUDE ONLY) consists of the Sun's observed altitude when the rate of change is near zero, a rough estimate of GMT at the time of the sight, and also height of eye, maybe atmospheric conditions, and finally the direction that the observer was facing (north or south) while taking the sight. That's all obvious, of course (though many people forget to include the compass direction). I'm just listing it out for completeness. Did I miss anything?

    Also note that Pidgeon's use of LAN for longitude is low accuracy from the outset and susceptible to a number of serious errors. But again, he was a yachtsmen, an adventurer, with the freedom to sail when convenient and with little regard for efficiency or accounting. Note, too, that this highly simplified "time by LAN" method (no LAN curve, no equal altitudes) works much better in the tropics. The "hang" of the Sun near noon can be quite short, easily less than 15 seconds, and also the correction for north/south vessel motion is much smaller. So if you're sailing in the tropics when the Sun's altitude is high and you're crossing the ocean more or less east/west, this method of estimating longitude can be quite acceptable, accurate to within five miles. But OUTSIDE the tropics, say in latitude 45°, the observed hang time where the altitude doesn't change much can be a couple of minutes. The correction for motion can also be a few minutes. If they combine in the same direction, your estimate of noon can be wrong by five minutes equivalent to over a degree error in longitude. A longitude that's off by a degree or even two is still useful if the only goal is to continue across the mid-Pacific. And there's nothing wrong with it as long as a navigator is prepared for more careful methods when approaching land.

    You wrote:
    "Perhaps he could have performed a time sight reduction by breaking up the reduction into multiple sessions with breaks for above deck air and horizon gazing."

    Or he could have done all the work on deck. Or he could have just "toughed it out". This again is a measure of the freedom available to an adventure sailor. Necessity is a great cure for a little seasickness: you get the work done or you get yelled at (or miss your destination, or arrive late with your cargo, etc.).

    -FER


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