Ruby wrote: >Could someone please help a floundering beginner in the fascinating >world of gnomonics? I have two questions.
>1. First, what is the purpose of the horizon ring in an armillary >sphere? Originally, armillary spheres were used to take readings of the positions of stars, each hoop being divided into degrees and having a pair of sights on it. Not having actually seen one of these (except as an illustration) I'm guessing a bit, but I imagine that once set it would be very easy to convert from right ascention/declination to altitude/azimuth, when the horizon ring would presumably come into its own. Now the sights have gone, as have the degree divisions, to be replaced by hour lines. A once great astronomical instrument reduced to a mere sundial - How are the mighty fallen ;-) David Higgon
