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    Re: CelNav without sextant
    From: Alexandre Eremenko
    Date: 2004 Nov 2, 21:19 -0500

    Frank:
    
    On Tue, 2 Nov 2004, Frank Reed wrote:
    
    > Maybe we should experiment. How many occultations
    > can you observe during the
    > next couple of months?
    
    I will experiment, of course. The main obstacle is the bad weather:-(
    I suppose there are many occultations, if you take
    more stars into account. (Unfortunately the nautical almanac
    has too few stars:-(
    
    My main question was how precisely you can time a sunrise/set
    and what is the role of the refraction here.
    Unfortunately, I cannot experiment in this area
    for the simple reason that I have no horizon:-(
    
    > the way, if you're excluding sextants, should you
    > also exclude binoculars, or do we permit them?
    
    I'd try both variants. Though I do not expect much improvement.
    Maybe it will help with Moon/stars.
    But what sort of filters can be used to look
    at the Sun through binocilar, so that the horizon remains visible?
    
    > with using the period when the Moon is moving with dark edge
    > trailing, too. An
    > attentive observer can time emmersions almost as well as immersions.
    
    This should be harder. But I have not experimented yet.
    
    > How much error are you guessing based on variable refraction?
    
    I have no idea. Chauvenet wrote somewhere, citing Bessel,
    that "No reliable refraction tables can be made for altitudes
    less than 5 degrees". I think, only an experiment can help
    to decide.
    
    I invite everyone to participate in this simple experiment:
    next time you enjoy a sunset in sea, look at your watch
    and record the time when the Sun touches the water:-)
    
    Alex.
    
    
    

       
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