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    Calculated Altitudes for Clearing
    From: Bruce Stark
    Date: 2002 Mar 24, 16:35 EST

    George has a point about calculated altitudes. But the explorers and
    surveyors of the past routinely left the altitudes to be calculated. They
    were using a different kind of nautical astronomy and a different kind of
    Nautical Almanac. It was only in the twentieth century, with the advent of
    the GHA Almanac, that navigators came to need accurate Greenwich time to work
    their observations. I've tried to show how the old system worked in a series
    of papers on Lewis and Clark's observations, published by the Navigation
    Foundation.
    
    But the point I particularly want to make is that people should observe
    distances wherever they are, without taking the time or going to the trouble
    of dealing with an artificial horizon. That way they will take hundreds of
    observations, not just one or two, and they will become familiar with their
    sextants.
    
    Artificial horizons are an important topic on their own. I've read some good
    advice, and done a bit of experimenting, but would not take many observations
    if it were mandatory to set one up every time.
    
    Haven't tried it yet, but I think we can figure out how to use our present
    Almanac the same way the old navigators used theirs.
    
    Bruce
    
    
    

       
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