Dear Don Christensen, I am pleased that your question on analammatic dials has been answered well. Tom McHugh offered the basic facts, Fer de Vries the mathematics, and Mac Oglesby a design program. In the spirit of international intellectual cooperation (competition?), I would like to match their offers and raise the stakes but adding declination lines!
In designing an interactive analemmatic sundial for the Calgary Science Center, I discovered the important the length of the shadow. The best user experience is achieved when the tip of their shadow intercepts the elliptical ring of hour markers. This shadow length varies with the latitude, solar declination, (seasons), time of day and height of the users. I rewrote an old program for analemmatic dial design as an Excel spreadsheet including tabular and graphical output of the usual X,Y coordinates on the ellipse for the hour markers and the Zodiac (where you stand) on the Y axis. I have now added to the graphical output, plots of declination lines defining the path of the tip of the shadow as a function of solar declination (date), dial size and gnomon height. Not only is it a great design tool but it allows the user to experiment with the input variables: latitude (including southern hemisphere as negative numbers), longitude correction options, declination, gnomon height, major axis size, etc. It taught me a lot about this type of dial and I would be happy to share it. If you can read and use Excel .xls files, I will send it out as an e-mail attachment to those that reply to this message. The usual freeware copyright, disclaimers and restrictions on commercial use apply. For those who received an earlier version, please replace it with this update. The original had significant errors and limitations. Roger Bailey Walking Shadow Designs, N 51 W 115 where I am amazed at what you can accomplish if you unplug your television. At 09:38 PM 4/6/99 -0700, Gordon Uber wrote: >Can anyone help Don Christensen? Please reply to him directly as well as to >Sundial List. He is not a subscriber. Thanks. > >Gordon Uber > >
