Hello Karl: Shadow shortening is unavoidable. So what's your solution? You certainly wouldn't dare make the gnomon taller than dictated by gnomonic laws so that the shadow looks right on the Winter Solstice. If you did that then the shadow would be too long on the Summer Solstice and would certainly throw time readings off too at certain times! There is no way around the shadow shortening problem on big dials I think. The shortening in the photo you used is only a couple of inches anyway. It was indeed greater in the early morning and late afternoon but hard to tell exactly how much because it was pretty fuzzy at those times.
I wouldn't go so far as to say that Joe Public thinks they are looking at another bad sundial. The clients never noticed and are quite happy with the dial since it seems to tell perfect time whenever they use it. At least that's what they tell me. The only possible solution I can think of would be a partial solution that might work for Winter Solstice date line readings only. This would involve placing the winter solstice line closer to the gnomon which would also be a clear violation of gnomonic laws. A scary thought! Anybody have any comments on this solution? (If the dial had multiple date lines, then you might put all the date lines closer to the gnomon by different amounts depending on how far away from the gmonon they are- The further they are away from the gnomon, the closer you'd need to shift them towards the gnomon. Lord only knows how you'd go about calculating the date lines for such a dial!) John p.s Wanna see some really bad dials? click here: http://homepage.ntlworld.com/jmikeshaw/page21.html -----Original Message----- From: Carl & Barbara Sabanski [mailto:[EMAIL PROTECTED] Sent: Monday, February 11, 2008 6:23 PM To: 'John Carmichael'; 'Sundial Mailing List (E-mail)' Subject: RE: Monumental Sundial Sunny Day John! I have looked at your photo of the nodus' shadow and it supports the comments I made regarding monumental sundials. The size of John's photo file is 483 kb so for those who have a problem with downloading such large files I have attached a much smaller file that shows the important part. You say that the shadow is much better than you expected. As seen by the messages, one can calculate and evaluate this discrepancy away. But you must be knowledgeable regarding things gnomonic. However, to Joe Public there is no way they would pick the winter solstice line as the point where the nodus is located. They would probably pick the point where the shadow is darkest, a significant distance away. The nodus is lost in the shadows. The time is also just after 11 a.m. and the shadow would be relatively short compared to the rest of the day where the error would probably be even greater. What would Joe Public say? What did the customer say! Did this meet their expectations or the project requirements (not necessarily the same)? I don't know. The were undoubtedly happy with the form but were they happy with the function. In any case, the point is if anyone is involved in the construction of a monumental sundial, particularly if you are charging for your services, the customer's expectations must be known. This will in turn become the requirements the diallist must meet. If the expectations cannot become achievable requirements the customer must be made aware of this or they will be disappointed. And Joe Public will think they are just looking at another sundial that doesn't work but it's big. Happy Dialling! Carl -----Original Message----- From: John Carmichael [mailto:[EMAIL PROTECTED] Sent: Monday, February 11, 2008 11:00 AM To: 'Carl & Barbara Sabanski'; 'Sundial Mailing List (E-mail)' Subject: RE: Monumental Sundial Hi Carl: We managed to get photos of the monumental sundial in Colorado Springs on the Winter Solstice. I have written an article about it that will probably be published in The Compendium, so I don't want to discuss the results too much here. But I will say that the long shadow of the gnomon's tip was much better than I expected it to be. The design of the gnomon tip is very important to minimize shadow shortening. Slender pointed tips are bad. You can see all the high def Winter Solstice photos at: http://advanceassociates.com/Sundials/COSprings/ Or just look at this one which I like a lot because of the snow: http://advanceassociates.com/Sundials/COSprings/Images/Chinook_Trail_Sundial _Winter_Solstice_3.jpg John -----Original Message----- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On Behalf Of Carl & Barbara Sabanski Sent: Sunday, February 10, 2008 4:43 PM To: Sundial Mailing List (E-mail) Subject: Monumental Sundial Sunny Day! It was a bright sunny day here in the Great White North. Sunny because it was about minus 29 degrees C. I went to the shed and got a couple of sticks, one being the handle from an old broom and the other from a rake. I am sure that most of you have done similar experiments. I stuck the broom handle vertically in the snow and the rake handle on a slant. The contrast of the shadows against the white snow was excellent. I have included a couple of pictures. Almost froze the fingers on my right hand getting these. Pic_1 was taken at the base of the sticks and shows how sharp the shadows are. Pic_2 shows the ends of the shadows. They are becoming very fuzzy. It is possible to determine the centre of the shadows but finding the edges is not an easy task. Zoom in and you will clearly see the. It was also obvious that the stick's shadows tapered significantly as you get further away from the base. Is this taper always the same? Probably not. It is also very difficult to find the tip of the stick's shadow. It is not where you think it is. And sometimes it is totally lost in the shadows. The longer the shadows become relative to the length of the stick the less distinct the shadow is. I viewed the shadow from a thin wire rod on the snow and very quickly there is no distinct shadow at all that could be used. I imagine these are the same issues that would be experienced in the design of a monumental sundial using a rod gnomon. If the rod casts an extremely long shadow and you must use this shadow to tell the time there will be a point where the shadow is no longer useful. I would think the gnomon should be relatively long in comparison to the size of the dial plate to provide good shadows for reading. Having an extremely large sundial using a shadow casting gnomon and making it very accurate are probably mutually exclusive. There is no doubt a limit to the size of a sundial that will allow it maintain its function at a particular location for the entire year and for all times it is illuminated. So if its big it better be spectacular so people don't really notice that it isn't working that well. Like the Sundial Bridge. This would also apply to a nodus. I would guess John that your sundial at the Colorado school might be experiencing this. I believe its gnomon ends at a tip. I believe the shadow of this tip may be lost in the shadows at this time of year. If not it would be interesting to know as the sundial is quite large and also a bit further south than my handles. There is a 60 metre horizontal sundial located in Lloydminster Alberta/Saskatchewan in Canada. It uses a rod gnomon but I have never seen it and do not know how well it works. It appears to have only the full hour lines so the designer may not have been trying for the accurate indication of time. It is simple but impressive because of its size. You can see it at: www.mts.net/~sabanski/sundial/sotw_canada_lloydminster.htm Anyway, biggest is not always better. There must be a balance between the form and its function. A monumental sundial need not be the biggest sundial. If you have a sundial, large or small, that you have built or are involved in building share it with the rest of us. It will help to motivate others to try to build their first sundial. Happy Dialling! Carl Sabanski www.mysundial.ca --------------------------------------------------- https://lists.uni-koeln.de/mailman/listinfo/sundial
