Good wishes to all in 2019 Has anyone come across the term 'azimuth or azimuthal circles' in the context of sundials in the 16th or 17th centuries? It would be useful to know for some work I am doing and to have a definition of what this term means. I don't think it relates to altitude and azimuth in our familiar horizon coordinate system. In which case does it relate to another coordinate system and if so which one? Or is it something else relating to sundials?
Very grateful for help that anyone can offer Alastair Hunter Edinburgh, UK -----Original Message----- From: Frank King [mailto:f...@cl.cam.ac.uk] Sent: Thursday, 3 January, 2019 3:07 PM To: a...@3peel.co.uk Cc: sundial@uni-koeln.de; Frank King <f...@cl.cam.ac.uk> Subject: Re: Gnomon Gap Puzzle - wonderful Dear Alastair, Many thanks for your kind words... > Your design is wonderful... I hope you enjoy the book. You ask... > ... have you come across the term 'azimuth > circles', how would you define this term? I have heard this term in several contexts. In an astronomical context, any great circle that runs from your local zenith via the horizon down to the out-of-sight nadir is sometimes called an azimuth circle. As it happens, I call this a vertical circle; that's just habit but see later. In another context, I actually OWN an azimuth circle... I have an army marching compass (magnetic) which has an annular ring supporting the glass cover. The instructions call this the "azimuth circle". There is a radial line on the glass marked in luminous paint! The idea is that if you want to march towards some distant point, you aim the body of the compass at that point and then twiddle the azimuth circle so that the radial line covers the large N for north on the compass card. This N is also in luminous paint. I expect the whole thing is radio-active! You then walk along (er, MARCH along) keeping the line on top of the N. A more common azimuth circle is the horizontal graduated ring on a theodolite which enables you to determine the difference in bearing between two terrestrial objects. More generically, an azimuth circle seems to be any ring which is mounted in a horizontal plane and which can either be twiddled round itself or it is fixed and something else rotates round within it. In my opening example this means the entire horizon is an azimuth circle; it runs round all the vertical circles. That's one reason I call them vertical circles rather than azimuth circles! Some technical terms can be confusing :-) I expect Mr Google can give you more examples. Very best wishes Frank --------------------------------------------------- https://lists.uni-koeln.de/mailman/listinfo/sundial
