Hi Willy:
Of course you are right that only a Solar Time dial can give Solar Time. But I must respectfully disagree with this comment: The opinion of non-dialists should not affect us. Almost all of my customers are non-dialists. They are not astronomers. (except for a few planetariums and schools). All my clients want to be able to glance at their sundial and know what time it is. Most of them could care less about Solar Time. We have a saying here: "The customer is always right". So I give them what they want. But I do ask them before I build their sundials what kind of time they want. I also offer Daylight Saving dials. In all my years of making sundials, I have never had a single customer who requested a Solar Time dial. If I ever do get a client who wants a Soilar Time dial I would give them what they want. I offer them, but they NEVER want one! It is my job to give my customers what they want. I do however give them an Owners Manual that explains Solar Time for those of them that are interested in astronomy. Respectfully, John From: Willy Leenders [mailto:[email protected]] Sent: Sunday, February 13, 2011 11:24 AM To: John Carmichael Cc: [email protected] Subject: Re: part 2 of longitude correction John, The main argument for an uncorrected time on a sundial, anywhere in the world, is that the correction removes an information that only a sundial can give, namely solar time. How about an astronomer who corrects his device indicating sidereal time to transform it in a clock time indicating device? The opinion of non-dialists should not affect us. It is our job to inform them about the difference between solar time and clock time. Willy Leenders Hasselt in Flanders (Belgium) Visit my website about the sundials in the province of Limburg (Flanders) with a section 'worth knowing about sundials' (mostly in Dutch): http://www.wijzerweb.be Op 13-feb-2011, om 18:28 heeft John Carmichael het volgende geschreven: My friend, Jim Tallman and I have had many discussions about longitude corrected dials. I know that many of the Western European dialists don't like longitude corrected dials- especially the British dialists. I can see why they feel this way. Their three biggest arguments against longitude corrected dials are these: 1) They aren't traditional, 2) They aren't symmetrical, 3) They are so close to their Prime Meridian that the longitude correction is quite small and almost insignificant. But there are equally good arguments for longitude corrected dials! In The United States, and many other places, the sundial may be located far away from the Prime Meridian at the edge of a Time Zone. In a perfect World, a Time Zone would only span 15 degrees. But most of our Time Zones have wiggly irregular boundries that sometimes span distances far greater than 15 degrees. Russia is an extreme example of this! There are parts of Russia that are missing entire zones! Then there's China. The entire country only has one Time Zone! See: http://www.travel.com.hk/region/timezone.htm For places like these, a well-built traditional Solar Time sundial will give a time reading that can be more than an hour off of Watch Time (Standard Mean Time). A casual non-dialist would say that these sundials don't work, especially if there is no Equation of Time graph available with built-in longitude correction! Correcting a dial for longitude solves this problem. For this reason, I think longitude corrected dials are more user-friendly. This is why Jim and I routinely make our dials with longitude correction. That's my two cents worth. John Carmichael From: Jack Aubert [mailto:[email protected]] Sent: Sunday, February 13, 2011 9:14 AM To: 'John Carmichael'; 'Donald Christensen'; [email protected] Subject: RE: part 2 of longitude correction This has all been very instructive. I am not a complete beginner, but have to confess that I was under the impression that rotating the dial plate with respect to the fixed gnomon was sufficient. Somebody once told me I could do this and I never really thought about it. If you actually think about the longitude correction, it does become obvious that just rotating the dial plate is not going to be right. For any dials I have made, I either used one of the programs like Shadows Pro or Orologi Solari to include a longitude correction, or more frequently, now, I use a delta cad macro and keep uncorrected solar time. I agree with Willy Leenders that sundials should tell solar time. I have a watch that can tell me mean time, but it has ceded to my celphone which is even better. Thanks for the question and thanks for the good answers. I keep learning things here, many of which I should already know but somehow missed. Jack From: [email protected] [mailto:[email protected]] On Behalf Of John Carmichael Sent: Wednesday, February 09, 2011 6:46 PM To: 'Donald Christensen'; [email protected] Subject: RE: part 2 of longitude correction (I hit the wrong button in my last email and it went out without my letter- sorry!) Hi Donald: I understand your question, because I had this same question years ago when I was a beginner. The answer is no. To re-phrase your question so that everybody understands it, you are asking this- When drawing a sundial face, should you simply rotate the normal solar time hour lines about their center of origin by 3 degrees to obtain a longitude corrected face? No, you can not do this. Each hour line has to be calculated and drawn individually. This is a common error some beginning dialists make when designing longitude corrected dials. I almost made this mistake too once! To help you out (since a picture is worth a thousand words) I drew your sundial in five minutes using Shadows Pro and sent it you off list the drawing. I just didn't want you to make a common mistake. But verify it for yourself and don't take my word for it. That's how you learn! Keep asking good questions! Thanks John From: [email protected] [mailto:[email protected]] On Behalf Of Donald Christensen Sent: Wednesday, February 09, 2011 3:52 PM To: [email protected] Subject: part 2 of longitude correction I'm laying out lines for a new dial I may not have been clear. I don't intend to rotate the gnomen. The dial will still point true north By labeling 12:12 as noon and 13:12 as 13:00, I am rotating the hour marks. My question is, Is it by an even 3 deg? -- Cheers Donald 0423 102 090 This e-mail is privileged and confidential. If you are not the intended recipient please delete the message and notify the sender. Un-authorized use of this email is subject to penalty of law. So there! --------------------------------------------------- https://lists.uni-koeln.de/mailman/listinfo/sundial
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