Dave, Only a p p a r e n t l y all dates from the Vernal Equinox through Summer to the Autumnal Equinox, passed through that same point, and only with latitudes of about 40 degrees. When you generate a serial of dials for 65 degree you can see more difference.
The distance from the centre of the ellips to the end of the shadow = a tan(delta) cos(phi) + h tan(phi + delta) with a = the semi major axis delta = declination of the sun phi = latitude Willy Leenders 509 N 54 E Dave Bell wrote: > This is great! Thank you for sharing it, Helmut. > > After downloading it, I couldn't help playing with it for a while... > I noticed something I hadn't before; maybe someone more knowledgable about > analemmatic dials could explain it for me: > > I generated a series of dials, with the sun-path set for the major quarter > points of the year, starting with the Summer Solstice. I noticed that > three of the four paths all crossed the minor axis at the same point, but > the Winter path was (more like I expected) 'way north of the ellipse. I > ran more, filling in the missing months, and found that apparently all > dates from the Vernal Equinox through Summer to the Autumnal Equinox, > passed through that same point, while all dates in the remainder of the > year were progressively farther North, with a maximum at Winter Solstice. > > Why don't the summer-ish paths fall to the South of the singular point? > > Dave > 37.29N 121.97W > > On Mon, 15 Apr 2002, Sonderegger Helmut wrote: > > > Hi to Everybody, > > > > some time ago Roger Bailey designed an Excel-spreadsheet for analemmatic > > sundials. I think, it was a presentation for the NASS-meeting at Hartford. > > I made some changes and added some features. For those who are interested, > > please download the extended version ANALEMM.zip from my homepage > > http://webland.lion.cc/vorarlberg/280000/sonne.htm > > (offered with permission by Roger). > > > > Hints at errors or any suggestions would be appreciated! > > > > Helmut Sonderegger > > > > - > > > > - -
