Hi John, Yes, I know and this is why a suncompass works. It's one scale of date with a number of ellipses for different latitudes around it. With one remark. At higher latitudes the length shrinks and final to zero at latitude 90.
And look at the formula: y = a cos phi . tan decl a cos phi is constant for a certain dial so y always is proportional to tan decl. But your remark is a very practical help to simplify the job. 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: "John Carmichael" <[EMAIL PROTECTED]> To: <sundial@rrz.uni-koeln.de> Sent: Monday, June 02, 2003 9:57 PM Subject: Re: your webpage > Hi Helmut & others: > > I'm sure you probably know this already, but one neat and helpful thing I > learned about analemmatic date line construction is this: > > > > All analemmatic dials at every latitude and of every size use the same date > line; the only difference is in the length of the line which becomes longer > (in relation to the ellipse) at higher latitudes and with bigger dials. But > the date line is the same for all. The distance between the date markings is > proportionally the same, no matter what length the date line. > > > > In other words, you don't have to redraw the date line everytime you design > an analemmatic for a different latitude or of a different size. You just > need one drawing and you can use it as a template for any analemmaic dial. > All you need to do is to change its size. If you use Delta Cad or > photocopyers, this is an easy operation. > > > > To determine the length of the date line is simple. First, you determine the > location of a focus point using traditional methods or Fer's Delta Cad > macro. Then draw a horizontal line to the center of the dial (the > North/South Meridian). This point is the equinox date on the date line and > is at the center of the line. Then draw an angled line from the focus that > is 23.44 degrees from horizontal. Where this line crosses the meridian is > one end of the date line and marks a solstice date. Measure an equal > distance in the other direction an this is the other end of the line and is > the other solstice date. The distance between these two points is the length > of the line. > > > > Then just blow up or shrink the size of your template drawing so that it is > the same length. Simple! And this saves a lot of work. > > > > Note: Here is a PDF of my Delta Cad Date Line Template. Of course you can > change font type and scale if desired. And you can have the option of a > clockwise or counterclockwise date notation. Both are shown here. > > > > John > > John L. Carmichael Jr. > Sundial Sculptures > 925 E. Foothills Dr. > Tucson Arizona 85718 > USA > > Tel: 520-696-1709 > Email: [EMAIL PROTECTED] > Website: <http://www.sundialsculptures.com> > ----- Original Message ----- > From: "Helmut Sonderegger" <[EMAIL PROTECTED]> > To: <sundial@rrz.uni-koeln.de> > Sent: Monday, June 02, 2003 3:52 AM > Subject: your webpage > > > > Fer, > > I just had one more look on your webpage with the information on > analemmatic > > sundials. Therefore my question: Why did you not include the formula for > the > > date points of the dial? I know, one can see that very easy from the > images > > there, but perhaps it would be of some help for some visitors of this > page. > > > > sunny greetings > > Helmut > > > > - > > > -
