Hi Anselmo and All, When I needed an answer to this question, I developed a spreadsheet to calculate and chart the path of the gnomon's shadow through the day and the seasons. The input variables are location size, gnomon height and solar declination. I gave the results at a NASS conference with a presentation "How Long is my Shadow: The Use of Declination Lines in the Design of Analemmatic Sundials". I can send you the presentation as a PowerPoint or pdf file on request. The files are fairly small as the 35mm slides used in the presentation are not included. All the math is. The spreadsheet was improved by Helmut Sonderegger and the features built into his excellent program "Alemma". This is available to download from his website http://web.utanet.at/sondereh/sun.htm .
The quick answer is ~5 meters for the major axis. The height of the gnomon is a factor. With your 30 cm step, the dial could be larger and less underwhelming. Regards Roger Bailey Walking Shadow Designs N 48.6 W 123.4 -----Original Message----- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] Behalf Of anselmo Sent: April 7, 2005 11:23 PM To: [email protected] Subject: On the greatest size of an analemmatic Dear all, I need your opinions and advice on which could be the greatest *effective* size of an analemmatic sundial for average latitudes. As you all know, for latitudes about 40 deg, the least longitude of the style equals more or less the major semiaxis of the ellipse so that the shadow can reach the ellipse on the worst case, this is, at summer solstice noon. However, in practice it could be too conservative to suppose so (who, except us, stands on an analemmatic in the worst of summer?), and perhaps there are some practical rules you know... Any hint? I am considering that the date scale can be on a 30 cm high step where the user gets up to and that the user can rise his/her hand so that the effective height of the style could be around 220 cm or so. Best regards, Anselmo - -
