Hi John et al, I thought at first that John Lynes was making a joke, but you could actually do this. If you have a large, fixed, plane mirror you can use the sunlight reflected off it instead of the actual sun. By suitably angling the mirror you can make the sun appear to rotate about any desired axis, not just the earth's axis. So, you can make it appear to rotate about the local vertical, just as it does at the Poles. So, just as at the Poles, an analemmatic sundial using the reflected light will be circular and the gnomon/person will not need to be moved for different seasons. But the numbers will go round anticlockwise, which might cause further objections!
The actual angle you'd need is this, I think: take a vertical mirror, facing south, then lean it towards the north at (90+latitude)/2 to the horizontal. For 40 degrees North this makes 65 degrees. So, it's facing the southern sky, as it were. If it were a dialface we'd say it was a direct south reclining dial. Fix it there. Now, put a vertical gnomon close to the bottom centre of the mirror and mark out a perfectly semicircular, equiangular dial around it. It will work from 6am to 6pm throughout the summer. Or, if you want the user to be the gnomon, just mark the spot where they must stand. In the winter months, as John said, the sun's too low in the sky for the reflection to shine on the ground. A mirror of, say, four feet high and eight feet wide would work well. It doesn't have to be 100% perfect optical quality. Users should back up to it to avoid being dazzled, I suggest. I think this is an excellent solution to what at first appeared an impossible brief. Regards Chris ----- Original Message ----- From: John Carmichael To: [EMAIL PROTECTED] ; [EMAIL PROTECTED] ; [email protected] Sent: Monday, June 09, 2008 3:42 PM Subject: RE: Advice wanted, on 'Analemmatic' sundial orientation Hello John L. I’ve never heard of such a sundial and I can’t imagine how it would function. I’m not sure I understand the setup and positioning of the mirror. Is the mirror permanently fastened to the ground or is the mirror moveable? Does the mirror reflect sunlight onto the sundial face, or do you read the sundial by looking at the face’s reflection in the mirror? I just don’t get it. It sure would be helpful to see a drawing if possible. Puzzled in Tucson John C. From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On Behalf Of [EMAIL PROTECTED] Sent: Monday, June 09, 2008 4:08 AM To: [EMAIL PROTECTED]; [email protected] Subject: RE: Advice wanted, on 'Analemmatic' sundial orientation Dear Alison One expedient, at least in theory, would be to fix a plane mirror, suitably angled in plan to the main driveway and tilted to convert the analemmatic sundial ellipse into a circle. The position of the human gnomon would not vary with the season. The sundial would receive reflected sunlight only on six months of the year, during the summer months, but this is when most visitors would be around. Unfortunately you would need either an enormous mirror or a very modest analemmatic sundial. John Lynes -----Original Message-----From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] Behalf Of Alison ShieldsSent: 03 June 2008 18:57To: [EMAIL PROTECTED]: Advice wanted, on 'Analemmatic' sundial orientation Dear Sundial Experts, I have recently joined this Mailing List, and hope that any memberswill be able to give me some assistance on the following situation. Our local Stately Home ("Kentwell Hall", Long Melford, Suffolk) isconsidering installing an Analemmatic sundial, as a new interactiveattraction for visitors - but we are getting 'conflicting' advice,on whether this 'Human Sundial' will work in the way we want it to. We have been in discussion with "Modern Sunclocks" (apparently theacknowledged 'experts' for these features), who have told us thatits central scale of dates must be aligned North/South - plus thathour markers must be correctly positioned on an elliptical ring,and which would lie on the Northern side of that scale of dates. Photographs on their website ( www.sunclocks.com ) confirm this. However, our 'Director of Operations' (Mr Phillips) absolutelyINSISTS that he wants the scale to run exactly parallel with ourmain driveway - on a compass bearing which is about 162 degreesfrom North, with the hour points placed on its Southern side. He also wants the hour points to form an exact semi-circle, andnot be elliptical in shape. Mr Phillips refuses to accept thathe cannot arbitrarily position the Human Sundial feature as hewishes, and says that it must be possible to create this so thatit could then align with the existing layout of buildings/paths. Can anyone on this Mailing List tell me whether it is possible toinstall a Human Sundial to fit any existing orientations, (withappropriate re-calculation of its component parts) - or, if not,just confirm that it must be as "Modern Sunclocks" have told me. I can then show the 'weight of evidence' to Mr Phillips. Because"Kentwell Hall" is a well-known Stately Home (open to the public),we should not want to become a 'laughing stock' by installing afeature which does not work - despite Mr Phillips assurance that"all types of sundial can be adjusted to work, in any location". Looking forward to all comments (to this List, or sent privately). Sincerely, Alison Shields. ---------------------------------------------------https://lists.uni-koeln.de/mailman/listinfo/sundial ---------------------------------------------------https://lists.uni-koeln.de/mailman/listinfo/sundial ______________________________________________________________________This email has been scanned by the MessageLabs Email Security System.For more information please visit http://www.messagelabs.com/email ______________________________________________________________________ ------------------------------------------------------------------------------ --------------------------------------------------- https://lists.uni-koeln.de/mailman/listinfo/sundial
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