Hi Frank, You are constructing a sun compass with the Weir diagram, based on the analemmatic sundial. A lot has been written about.
Have a look in Compendium, september 2003 for the article >From Universal Analemmatic To Sun Compass - Filling The Gaps by Frederick W. Sawyer Best wishes, Fer. Fer J. de Vries De Zonnewijzerkring mailto:[EMAIL PROTECTED] http://www.de-zonnewijzerkring.nl Home mailto:[EMAIL PROTECTED] http://www.iae.nl/users/ferdv/index-fer.htm Eindhoven, Netherlands lat. 51:30 N long. 5:30 E ----- Original Message ----- From: "Frank Evans" <[EMAIL PROTECTED]> To: "Sundial" <[email protected]> Sent: Thursday, February 03, 2005 10:18 PM Subject: azimuth diagram > Greetings fellow dialists, > > The other day I bought a copy of Weir's Azimuth Diagram. This was the first > time I had seen it although I had read about it in earlier days. It is a > remarkable document, devised by Captain Weir in 1890. Its purpose is to > enable a navigator to find the azimuth of a heavenly body by graphical > means. > > In appearance it is a circle of 50 cm diameter on paper, containing a > central vertical ordinate, a series of concentric ellipses and mirrored > hyperbolic curves spreading from the central ordinate. It makes a very > pretty picture and is in colour. The diagram is entered with the elements > latitude (expressed as an ellipse), declination of the heavenly body > (expressed linearly on the vertical ordinate) and the hour angle (crudely, > sun time) of the heavenly body (expressed as a hyperbolic curve). Marking > the declination on the vertical ordinate (which is pricked out in degrees > from 65N to 65S) and joining this point to a second point where the > appropriate latitude ellipse crosses the hour angle hyperbola gives a line > which plots the azimuth of the heavenly body in question. > > It occurred to me that this graphical method of solving azimuth problems > could be modified to make a sundial. If the Weir diagram were to be levelled > and oriented N and S and a vertical shadow pin were placed on the central > ordinate at the sun's declination then the shadow would represent its > azimuth. Follow this until it reaches the appropriate latitude curve and > read off the time from the conjoined hour angle curve. > > Two points (1) This diagram is a fascinating survival, last printed in 1950 > and still obtainable from UK Admiralty chart agents. It is catalogued as > chart no. 5000 and is printed on good quality chart paper. It costs 5 pounds > 50. There is a second diagram available for the hardy ones, extending from > 65 deg to 80 deg. > > (2) Have I got all this right? Is anyone else familiar with Weir's diagram > and has it been mentioned before in this sundial group? > > Frank 55N 1W > > - -
