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    Re: Artificial horizon question
    From: George Huxtable
    Date: 2009 Apr 20, 12:09 +0100

    Peter Hakel asked
    
    ...... And to take it one notch further, how about an artificial horizon for
    the stars and planets (at night, of course)?  Are there any systematic
    methods to ensure that the star reflected on the surface is indeed the one I
    intend to observe?
    
    =============
    
    For stars at night, there's no good substitute for a pool of Mercury. And
    with an artificial horizon, your use of stars is no longer restricted to
    twilight, so you can wait until the sky gets really dark before you take a
    round of star-sights. But if other fluids such as water are used as
    reflector, the sky here in the UK seldom gets clear and dark enough for
    stars to be seen clearly..
    
    However, the archives of this list (or, more likely, its predecessor, nav-l)
    should contain postings by Kieran Kelly, who enlivened our pages for a time
    by postings of his overland navigation, by horse and by camel, in the
    Australian outback. He described the navigation in the desert of Augustus
    Gregory, whose journeys from the 1840s Kelly was following.
    
    Gregory' navigated mainly by sextant altitudes of stars, which were
    reflected in a pannikin of black tea, which he could then drink; which shows
    that the method can work in the right circumstances. I expect that the clear
    desert air produced suitably bright stars with dark backgrounds. Presumably,
    there would have to be a camp-fire lit so a colleague could read the sextant
    by its light and note the results, though Gregory himself would need to
    preserve his night-vision, perhaps by keeping his distance from the fire and
    putting his back to it.
    
    Gary has described well how the right star is to be found.
    
    George.
    
    contact George Huxtable, at  george{at}hux.me.uk
    or at +44 1865 820222 (from UK, 01865 820222)
    or at 1 Sandy Lane, Southmoor, Abingdon, Oxon OX13 5HX, UK.
    
    
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