Dear Willy
Im not sure I agree with you. I think the empirical method automaticly corrects for the longitude shift. If you mark the shadows location using a watch on a day when the EOT is zero, then the longitude correction is there. The sundial will be marking watch time when the EOT is zero. The longitude correction will be built in. I look at it this way. My sundials that I make are all corrected for longitude when I make them. If I were to erase all the hourlines on one of them, I could recreate the erased lines by using the empirical method without making further corrections for longitude. I think I am correct in this. But Ive been wrong on many things in the past so Im willing to listen to someone tell me why I am wrong. Respectfully, John _____ From: Willy Leenders [mailto:[EMAIL PROTECTED] Sent: Thursday, June 21, 2007 1:17 PM To: John Carmichael Cc: 'Andrew Corl'; 'Sundial List' Subject: Re: Direct South Dial Hi John, Using your empirical method, not only the equation of time must be zero, you have to take in account the correction for longitude. Willy Leenders Hasselt in Flanders (Belgium) Op 21-jun-07, om 21:24 heeft John Carmichael het volgende geschreven: Hello Andrew: There is an easy way to mark the hourlines on a satellite dish or any surface for that matter, without using any formulas or math. Use what some call the empirical method. This method is useful for oddly shaped surfaces. 1. Position the dish in the direction that you want it to face. (Due south or even slightly away from south. It doesnt matter.) 2. Attach your gnomon so that the shadow casting edge points directly at the north celestial pole (Youll probably attach it at the center of the dish, and you will probably be using a rod gnomon, but it could be attached anywhere. It doesnt matter). 3. On a sunny day, when the Equation of Time is zero (the next date this occurs is September 1st), using an accurate time source, mark where the gnomons shadow falls on the dish at the times you want to indicate (hours, ½ hours, ¼ hours, whatever). 4. Done! Your sundial will now indicate solar time adjusted for longitude. You can mark your sundial in the same fashion on any day of the year if you take into consideration the Equation of Time value for the date that you do it. Real easy! John L. Carmichael Sundial Sculptures 925 E. Foothills Dr. Tucson AZ 85718-4716 USA Tel: 520-6961709 Email: [EMAIL PROTECTED] My Websites: (business) Sundial Sculptures: http://www.sundialsculptures.com <http://www.sundialsculptures.com/> (educational): Earth & Sky Equatorial Sundial: http://advanceassociates.com/Sundials/Earth-Sky_Dial/ (educational) My Painted Wall Sundial: http://www.advanceassociates.com/WallDial (educational) Painted Wall Sundials: http://advanceassociates.com/WallDial/PWS_Home.html (educational) Stained Glass Sundials: http://www.stainedglasssundials.com <http://www.stainedglasssundials.com/> (educational) Sundial Cupolas, Towers & Chimneys: http://StainedGlassSundials.com/CupolaSundial/index.html _____ From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On Behalf Of Andrew Corl Sent: Thursday, June 21, 2007 10:27 AM To: Sundial List Subject: Direct South Dial Greetings all, Several months ago I bought a house and the previous owners left me with one of those 12" diameter satellite dishes. I have no need or want of Direct TV or satellite TV. I was sitting there thinking one day that it would make a really nice direct south facing sundial. My house already faces a little east of south anyway, and the location where the dish is gets direct sunlight almost all year round. My questions is this: Do I need to make any adjustment in the calculations of the hour lines for the shape of the dish? If so what is the formula? I am going to install a simple style using a metal road about a half inch in diameter. I want this sundial to tell solar time not necessarily actual time. Though one day I may install an equation of time underneat the dial . _____ Boardwalk for $500? In 2007? Ha! Play <http://us.rd.yahoo.com/evt=48223/*http:/get.games.yahoo.com/proddesc?gameke y=monopolyherenow> Monopoly Here and Now (it's updated for today's economy) at Yahoo! Games. --------------------------------------------------- https://lists.uni-koeln.de/mailman/listinfo/sundial
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