"A very interesting dial" continued
The note below is from David Potter who made the dial discussed as "A very interesting dial" earlier on the list. Mr Potter tried to join the list, but his browser indicated that the security of the subscribe site was questionable. The dial and a number of photos can be seen on the NASS Register. Click on "Colorado" then scroll down to Englewood #T003 === Mr. Potter's note to me. === Wow! I enjoyed listening to the conversations from the experts. You are correct that most of the discussions resolved themselves. Regarding the strange compass rose: When the tower was being constructed, before the idea of a compass rose even entered my mind, I agreed to a 15 degree increment on the azimuth markers which were then imbedded in the wall. As a result the 22.5 degree pointer separation for a traditional compass rose would have caused confusion, so I went with pointers that match each vertical azimuth marker. Fortunately there is a marker at 45 degree increments. In order to make the clock work, the construction tolerances on the cylindrical wall had to be very tight. At the direction of Paul Hutton, the architect, they mounted a laser on the center of the floor, and aligned its vertical beam with the center of the aperture in the conical roof. They used the laser beam to mark the center of the circular rings, and were able to establish circularity within about 1/4 inch. That established the alignment for the entire cylinder, which made my work a lot easier. The inside wall is a cylinder, not a right prism. The ceiling, however is segmented into triangular planes, but you don't notice it due to the diffuse interior illumination. During early stages of construction, we had some students help establish true north. They set a thin vertical pole at the axis of the cylinder, then marked the location of its shadow on the perimeter foundation at solar noon. In spite of all this care, some of the vertical markers are off by as much as an inch; as I was rendering the clock I reestablished new data (using the 303-499-7111 time from the atomic clock in Boulder) and made necessary corrections so the analemmas would be accurately set. I am glad this has sparked some interest! Regards Dave --- https://lists.uni-koeln.de/mailman/listinfo/sundial
RE: A very interesting dial
David Potter, the dial's maker replies: In response to the question " Is any focusing involved?" No focusing devices are involved. However, the small 1/8 inch aperture acts as a camera obscura (a pinhole camera,) so the spot on the wall is a (fairly) focused image of the sun. I have not been able to see sunspots. When clouds pass over the sun, they show up clearly in the spot. For weather protection, the hole is covered by a 1" piece of plate glass. The top and bottom surfaces are parallel, so the incoming and outgoing rays are parallel. _ From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On Behalf Of Bill Gottesman Sent: Sunday, May 20, 2007 2:35 PM To: 'Sundial Mailing List' Subject: Re: A very interesting dial Fascinating. Does anyone know it the analemmas were placed after observing the movement of the sun, or before? i.e., how was it done? And, is there a focusing lens involved? And if so, how do they dealt with focusing it over such a variable distance? -Bill G. - Original Message - From: Robert <mailto:[EMAIL PROTECTED]> Terwilliger To: 'Sundial Mailing List' <mailto:sundial@uni-koeln.de> Sent: Sunday, May 20, 2007 1:32 PM Subject: A very interesting dial A new and very interesting, perhaps unique, dial has been added to the NASS Sundial Register. The dial is delineated on the inside walls of a purposely built tower. Indications include analemmas as well as altitude and azimuth. Go to Colorado, then scroll down to Englewood #T003 http://sundials.org/registry/ Bob Terwilliger NASS Webmaster _ --- https://lists.uni-koeln.de/mailman/listinfo/sundial --- https://lists.uni-koeln.de/mailman/listinfo/sundial
Re: R: Re: A very interesting dial
Dear Frank, Gianni, Robert, Bill and all, It seems that there is much interest in directly solving the multibody Kepler's law for at least those objects in our solar system. This is working from near basic principles rather than developing perturbations to curve fitting polynomial circular functions. The method allows for extremely good extrapolation rather than just the extremely good interpolation of of the trigonometric series approach. Trigonometric series may be the most efficient approximation methods, but cover only a very restricted range of the variables outside of which they fall apart rapidly. The method may seem, and in fact may be overkill, for the data extraction required to design and build a sundial but, a sundial is a fitting monument to the achievement of the method! Edley. --- https://lists.uni-koeln.de/mailman/listinfo/sundial
Re: R: Re: A very interesting dial
Dear Gianni, Mea culpa! You are of course right. The summer solstice arc indeed curves upwards on a cylindrical surface. I was assuming that the surface was made of flat segments (as in the external photograph) but this is not so. > - The higher line (at ¾ of the height of the > doors) (aluminium) is the 70° almucantarat > (constant-altitude curve) I hadn't noticed this but, again, you are right. Yes, I agree with that. > - The compass rose is of 24 points because from > each of them comes out one of the vertical azimuth > lines True, but azimuth lines are usually separated by 22.5 degrees or 11.25 degrees. > I don't understand why the planners have used a > program that solves Kepler's Laws... I agree. Kepler's laws are fine for an ideal case but the Earth's orbit is much more complicated than pure Kepler. A good exercise is to implement the Meeus algorithms. This takes a long time but when you have finished you understand how messy the Earth's orbit really is! Best wishes Frank --- https://lists.uni-koeln.de/mailman/listinfo/sundial
R: Re: A very interesting dial
Molto bella ! Very Fine ! From Google Earth we have Lat.=39d 38’ Long. =104° 56’ 25” E - the place is almost exactly on the 105d meridian with TZ=7h East (englewood, colorado,4000 quincy ave.) In my opinion : - the arc that touches the bottom of the noon analemma is certainly a part of the solstice line (brass) - The higher line ( at ¾ of the height of the doors) (aluminium) is the 70° almucantarat (constant-altitude curve) - The inside is a cylindrical surface with a radius of about 200 cm (80”) and with a conical roof with a slope of 26.9 d (=90-Lat-23.45) - The higher altitude curve ( third photo) is the 30d almucantarat - The compass rose is of 24 points because from each of them comes out one of the vertical azimuth lines I don't understand why the planners have used a program that Because of the fact that the year doesn't have an integer number of days it is necessary, in the calculation of sundials, to take into consideration not the exact values of the declination and of the TEq , but their mean values calculated in a period of at least 4 years (without considering the 29 February :-) ) Also a digital clock < to check the solar clock's accuracy> seems to me a little excessive. Gianni Ferrari P.S. One of my old programs calculates and draws these kind of sundials >Messaggio originale >Da: Frank. [EMAIL PROTECTED] >Data: 20-mag-2007 22.01 >A: "Robert Terwilliger" <[EMAIL PROTECTED]> >Cc: "Sundial Mailing List" >Ogg: Re: A very interesting dial > >Dear Robert, > >Indeed that is a very interesting dial. > >Do you have any idea what the arc is that touches >the bottom of the noon analemma? It can't be a >short length of constant-declination curve because >it is the wrong way up and it can't be a short >length of constant-altitude curve either (that >would be level on a true cylinder). > >The outside of the building suggests that the >cylinder is made up of flat faces. It is less >clear that the inside is also flat faces. > >Other random thoughts: > > 1. A problem with domed nickel nail heads is >that you get dazzling reflections at the >critical moments. > > 2. The compass rose is of 24 points. I am more >used to 8, 16 or 32 points. How common > are 24-point compass roses? They are >suggestive of hours of course but only >very loosely. > > 3. Any chance that 29 February features? :-) > >Frank King >Cambridge, U.K. > >--- >https://lists.uni- koeln.de/mailman/listinfo/sundial > > --- https://lists.uni-koeln.de/mailman/listinfo/sundial
Re: A very interesting dial
Dear Robert, Indeed that is a very interesting dial. Do you have any idea what the arc is that touches the bottom of the noon analemma? It can't be a short length of constant-declination curve because it is the wrong way up and it can't be a short length of constant-altitude curve either (that would be level on a true cylinder). The outside of the building suggests that the cylinder is made up of flat faces. It is less clear that the inside is also flat faces. Other random thoughts: 1. A problem with domed nickel nail heads is that you get dazzling reflections at the critical moments. 2. The compass rose is of 24 points. I am more used to 8, 16 or 32 points. How common are 24-point compass roses? They are suggestive of hours of course but only very loosely. 3. Any chance that 29 February features? :-) Frank King Cambridge, U.K. --- https://lists.uni-koeln.de/mailman/listinfo/sundial
RE: A very interesting dial
Bill, Above the first photo it says it was all done with a computer progam. I don't know about the focusing. Bob _ From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On Behalf Of Bill Gottesman Sent: Sunday, May 20, 2007 2:35 PM To: 'Sundial Mailing List' Subject: Re: A very interesting dial Fascinating. Does anyone know it the analemmas were placed after observing the movement of the sun, or before? i.e., how was it done? And, is there a focusing lens involved? And if so, how do they dealt with focusing it over such a variable distance? -Bill G. - Original Message - From: Robert <mailto:[EMAIL PROTECTED]> Terwilliger To: 'Sundial Mailing List' <mailto:sundial@uni-koeln.de> Sent: Sunday, May 20, 2007 1:32 PM Subject: A very interesting dial A new and very interesting, perhaps unique, dial has been added to the NASS Sundial Register. The dial is delineated on the inside walls of a purposely built tower. Indications include analemmas as well as altitude and azimuth. Go to Colorado, then scroll down to Englewood #T003 http://sundials.org/registry/ Bob Terwilliger NASS Webmaster _ --- https://lists.uni-koeln.de/mailman/listinfo/sundial --- https://lists.uni-koeln.de/mailman/listinfo/sundial
Re: A very interesting dial
Fascinating. Does anyone know it the analemmas were placed after observing the movement of the sun, or before? i.e., how was it done? And, is there a focusing lens involved? And if so, how do they dealt with focusing it over such a variable distance? -Bill G. - Original Message - From: Robert Terwilliger To: 'Sundial Mailing List' Sent: Sunday, May 20, 2007 1:32 PM Subject: A very interesting dial A new and very interesting, perhaps unique, dial has been added to the NASS Sundial Register. The dial is delineated on the inside walls of a purposely built tower. Indications include analemmas as well as altitude and azimuth. Go to Colorado, then scroll down to Englewood #T003 http://sundials.org/registry/ Bob Terwilliger NASS Webmaster -- --- https://lists.uni-koeln.de/mailman/listinfo/sundial --- https://lists.uni-koeln.de/mailman/listinfo/sundial
A very interesting dial
A new and very interesting, perhaps unique, dial has been added to the NASS Sundial Register. The dial is delineated on the inside walls of a purposely built tower. Indications include analemmas as well as altitude and azimuth. Go to Colorado, then scroll down to Englewood #T003 http://sundials.org/registry/ Bob Terwilliger NASS Webmaster --- https://lists.uni-koeln.de/mailman/listinfo/sundial
