Hi Frank and al, I have a couple of suggestions for using string and candle to determine polar alignment. The first string would be used with a weight as a plumb bob to bring the position of the star to the horizontal plane. The first use of the candle could be to light the string against the dark sky. Star finders for telescopes often use lighted reticles. With light pollution these days it is hard to think how dark it was by starlight in centuries gone by. Remember the old Moslem definition of dawn used to determine the fasting periods in Ramadan. It is dawn when you can see a grey thread (hair) against the sky.*
The second use of the candle might be to bring the position of the star to the vertical plane of the church wall. The candle would be moved along the wall until the observer noted that it lined up with the string of the plumb bob, right under the north star. A second plumb bob would be used to bring the position of the observers eye to grade level. This would establish a North South line in relation to the church wall that could be used to set the sundial. Of course they would do this at the time of culmination of Polaris as its rotation around the polar axis was well known centuries ago. Roger Bailey Walking Shadow Designs N 51 W 115 * I may have confused my references here. This may be the definition of dawn described in C.S. Forester's Horatio Hornblower series. My knowledge of Nelson's navy and Moslem religious practices are pretty vague. -----Original Message----- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] Behalf Of Frank Evans Sent: March 16, 2002 2:12 PM To: [email protected] Subject: old polar alignment Greetings fellow dialists, I recall reading somewhere that dialists in centuries gone by commonly used the pole star to align wall dials and that their equipment consisted of lengths of string and a candle. Can anyone throw any light on this? Obviously when setting up a dial on the south wall of a church, for instance, the dialist would have to be well away from the church to see the pole star. But why the candle? Nowadays it is beyond me why anyone would bother with the pole star at all, especially for a wall dial since unless it is north facing the pole star is on the wrong side of the wall while the sun is on the right side. And the sun throws a shadow, fuzzy but accurate enough for a sundial, which throws the same shadow, and its azimuth can be calculated for any time of day. Frank 55N 1W -- Frank Evans - -
