Re: sundial Digest, Vol 215, Issue 2
I think there's a simpler solution. In the UK at noon the shadow of the style on a horizontal sundial faces North - away from the sun. Turn the style through 180 degrees in a horizontal plane, and its shadow at noon will face South - towards the sun! John Lynes On Mon, 11 Mar 2024 at 17:12, Bill Gottesman wrote: > My guess on this one (without using mirrors): > Point the bottom of an empty can at the sun. The shadow inside the can > now points in the direction of the sun, though the definition of "in the > direction of the sun" in this case is debatable. > -Bill > > On Mon, Mar 11, 2024 at 9:33 AM Chris Lusby Taylor > wrote: > >> This reader has so far failed to see how a shadow can be in the same >> direction as the light source, if by that Frank means that it is between >> the object and the light. Perhaps Frank will enlighten us at next month's >> annual British Sundial Society Conference. >> >>> >>> Date: Mon, 11 Mar 2024 09:01:46 + >>> From: Frank King >>> Of course, a shadow CAN be in the same direcion as the light. I'll >>> leave that as an exercise for the reader :-) >>> >> --- > https://lists.uni-koeln.de/mailman/listinfo/sundial > > --- https://lists.uni-koeln.de/mailman/listinfo/sundial
Re: Sun elevation tool
There is a description of the TNO "jellyfish", as it was affectionally known, in a paper by J van der Eijk, "Instrumentation for Solar Studies", in the *Proceedings of the CIE Intersessional Conference on Sunlight in Buildings*, Bouwcentrum International, Rotterdam 1967, and reprinted as Publication 241 of the Research Institute for Public Health Engineering TNO, Delft. A more accurate instrument on similar lines was Gunnar Pleijel's "Globoscope", a convex paraboloid whose mirrored surface reflected a stereographic projection of the solar orbit and its surroundings. (G Pleijel, "The Computation of Natural Radiation in Architecture and Town Planning", Bulletin 25, Statens Namnd for Byggnadsforskning, Stockholm 1954). A cheaper Globoscope, based on a vehicle hub cap, was described by Professor P F O'Brien, of the University of California, Los Angeles, in the journal *Illuminating Engineering. * I don't have the reference handy. John Lynes On Wed, 26 Oct 2022 at 01:46, John Pickard wrote: > Good morning, > > Has anyone come across this dial-related device? > > > https://picclick.co.uk/ARCHITECT-TOOL-Window-SUNLIGHT-SUN-ELEVATION-Enraf-144741549298.html > > Cheers, John. > > Dr John Pickard. > > --- > https://lists.uni-koeln.de/mailman/listinfo/sundial > > --- https://lists.uni-koeln.de/mailman/listinfo/sundial
Fwd: The utility of sundials today.
I will list a few of my practical applications for a sundial with declination lines, in architectural and urban design. 1. Take an architectural model of a group of buildings. Place a small sundial next to the model with the north-point of the sundial parallel to the north-point of the model. (I use a sundial in a matchbox tray). Shine an electric lamp on the model. The shadow on the sundial will indicate the date and the time of day at which the sun will shine from that direction on the group of buildings. Note the times when each building will overshadow its neighbours, altering the layout to optimise solar penetration or protection. Ideally this is a job for three people. One to hold the lamp as far away from the model as possible to ensure near-parallel light. One to watch the sundial and tell the lamp-person to move up, down, left or right. One to photograph the sunlit model, taking care to note the time and date on the sundial in each photograph. 2. Alternatively, if the sun is shining, mount the model and sundial on a drawing board. Tilt and rotate the board so that successive shadows on the sundial indicate the times and dates you have chosen to study. 3. Instead of using an electric lamp indoors, view the architectural model by eye. Glance past the nodus to read on the sundial scale the time and date at which the sun would shine from the direction of your eye. Parts of the model you can see will then be sunlit. Parts concealed from your view will be overshadowed: a shadow is simply an area which the sun cannot see - the sun never sees a shadow. 4. Another application is to detect the periods at which a given piece of ground will be overshadowed, perhaps by trees or by surrounding buildings. Place a small mirror flat on the ground. Mark a cross on the centre of the mirror. Move your head to align the mirrored reflection of a possible obstruction to sunlight with the cross on the mirror. Without moving your head, place your small sundial over the cross, remembering to rotate the sundial so the its north-point faces south. Read past the nodus the time and date at which the direction of the sun will coincide with the direction of the potential obstruction. 5. If you turn a vertical sundial upside down and reverse it from left to right, the declination lines will form a perspective of the sun's apparent orbit across the sky. Indeed if you place your eye at the nodus of the rotated sundial, each point on the sun's path will appear in the same direction, in relation to your eye, as the real sun at the corresponding time of day. This feature is especially valuable when you are asked to investigate complaints of solar glare or distraction in a workplace. Superimpose your sunpath perspective on a photograph or perspective drawing of the environment and read off the time when the sun may be in view through a window. Obviously the orientation of the vertical sundial and the drawing or photograph must be the same, and the perspective distance of the drawing, or the effective focal length of the camera, must match the distance of the nodus from the plane of the sundial. So either the sundial or the photograph may need enlarging. 6. Finally if you need to design external shading to mitigate the effect of solar overheating, you can superimpose on the sunpath perspective a perspective of a horizontal canopy (a horizontal line seen from the window sill) or a vertical or sloping fin to show the percentage of window shielded from direct sunlight at different times of day or at different seasons. 7. ... and I'm told that sundials have also been used for telling the time ... ... John Lynes --- https://lists.uni-koeln.de/mailman/listinfo/sundial
Re: Dial face colouration
Hi Steve, I'm sorry I've confused you. The experiments reported in the 1941 UK paper were limited to illuminances not exceeding 10 000 lux. For that reason I had to admit that higher illuminances might well point to a different conclusion. I certainly did not intend to suggest that reflected light should be limited to 6000 lumens per square metre; simply that I have no experimental evidence handy for illuminances exceeding 10 000 lux. Weber's Law stated that if the background luminance is Lb and the stimulus luminance is Ls, then the just-detectable luminance difference (Ls - Lb), or in the case of a sundial (Lb - Ls), is proportional to Lb. If Weber's Law were correct then the perceived contrast of the shadow on a matt sundial plate would be independent of the reflectance of the plate. Although Weber's "Law" is approximately true, for many practical purposes, over a wide range of values for Lb, it certainly fails under dim lighting and under very bright lighting, when the "Weber fraction" (Lb - Ls)/Lb rises. Ideally for a sundial plate one would aim for the value of Lb which minimises the Weber fraction. Unfortunately there is little agreement over the precise value of Lb at which this minimum occurs. It is almost certainly greater than 10 000 lumens per square meter of reflected light but, as you have observed, well below the luminance of a white surface under intense sunlight. Once again I'm sorry to have confused you. The take-home conclusion is that there is no single ideal reflectance for the plate of a sundial. It varies with the sky illuminance. When Weber's Law prevails, a reflectance of about 60 per cent is likely to be a safe bet. John Lynes PS I'm away from my computer for the coming week, so will be out of touch for some time. On 28 February 2017 at 01:48, Steve Lelievre < steve.lelievre.can...@gmail.com> wrote: > John, > > Will you clarify some things for me? > > You mention that 50 lumens per square foot is about 500 lux, and that the > cited article recommends a limit of 60% reflectance for sky illuminance of > up to 1,000 lumens per sq. ft. If I multiple all that out, it would appear > to suggest a a limit of 6,000 lux of reflected light for comfortable > viewing. Is that the case? > > Through Google, I found empirical rules for calculating the wattage of > solar radiation reaching the ground, depending on season, altitude, > declination, hour angle, and geographic elevation. I also found a > conversation factor for converting sky illumination in watts per square > metre to lux. Putting it all together, I get a figure of about 72,000 - > 91,000 lux for the incident illumination, at noon on the northern > hemisphere summer solstice at sea level, depending on latitude (and valid > for mid-latitudes only). Using the mid figure of 80,000 lux, if I want to > limit the reflected light to 6,000 lux then the reflectivity has to be less > than 22.5%, which corresponds to a lightness of only 3.5 on the Munsell > scale. > > Does this conversion make sense, or don't things work like that? > > Of course, if we've gone out in midday sun, we should be wearing > sunglasses and, again from the web, sunglasses reduce the visible light > reaching our eyes by two thirds or more. If I factor that in, my Munsell > value rises to 5.3. And, as you pointed out, when the sun isn't so high in > the sky, we can tolerate a more reflectivity on our dial face. > > Thanks for any further comments or advice, > > Steve > > P.S. Based on what I've learned so far, I'm leaning towards using a > material with a Munsell value of 6 or 7, which would correspond to the > mid-grays, tans and browns that people have been suggesting may work in > practice. It would be the number you mentioned but with the lightness > notched down a little. My design latitude of 45N is a little further south > than England (where the article's authors came from) and the summer sun is > a tad brighter. As well, I reckon a suitable colour with a number of 6 or 7 > would look OK against a lawn, flowerbed or other greenery. > > > > On 2017-02-26 7:08 AM, John Lynes wrote: > > There is no single optimum reflectance for a flat dial face. Obviously > under dim sunlight the optimum reflectance would be 100 per cent, > i.e.perfect white. > Under intense sunlight, contrast sensitivity would be optimised for a > lower value of reflectance. Thousands of papers have been written on > contrast sensitivity. One classical study is "Brightness and contrast in > illuminating engineering" by RG Hopkinson, WR Stevens and JM Waldram, > Transactions of the Illuminating Engineering Society (London), Vol 6, No 3, > pp 37-48 (1941). This indicates that when the sky illuminance on a matt > dial face is over about 50 lumens per square foot (about 500 l
Re: Dial face colouration
There is no single optimum reflectance for a flat dial face. Obviously under dim sunlight the optimum reflectance would be 100 per cent, i.e.perfect white. Under intense sunlight, contrast sensitivity would be optimised for a lower value of reflectance. Thousands of papers have been written on contrast sensitivity. One classical study is "Brightness and contrast in illuminating engineering" by RG Hopkinson, WR Stevens and JM Waldram, Transactions of the Illuminating Engineering Society (London), Vol 6, No 3, pp 37-48 (1941). This indicates that when the sky illuminance on a matt dial face is over about 50 lumens per square foot (about 500 lux) the optimum reflectance would be about 60 per cent (a light grey, about Munsell Value 8). Below this illuminance (which would correspond to a solar altitude close to sunrise or sunset) the optimum reflectance would rise quite sharply. Note however that the maximum sky illuminance considered by the authors was 1000 lumens per square foot (corresponding to a solar altitude of about 20 degrees). Higher illuminances might further reduce the optimum reflectance. John Lynes On 26 February 2017 at 02:25, Michael Ossipoff <email9648...@gmail.com> wrote: > It seems to me that Steve's question has been mostly disregarded rather > than answered. > > Not having experience with translucent dial-faces, I didn't know about > their lack of accuracy, and I certainly can't disagree with what two people > have said about that. > > It means that the advantage of a translucent dial, for omnidirectional > reading, comes with a disadvantage of less precise accuracy. > > But of course a high-mounted dial intended for relatively distant reading > might not be as concerned with fine accuracy as with omnidirectional > viewing. And so translucent dials for all-directions viewing certainly > aren't ruled-out. > > Steve's main question was about the choice of dial-face hue, saturation > and brilliance, for easy and safe dial-reading. It seems to me that Steve's > question has been mostly disregarded and discounted rather than answered. > > I lied. > > I said that I can't speak from experience on that matter. > > But my experience with a few paper-on-cardboard tablet-dials is sufficient > to say this: > > From my experience, I can say that you definitely don't want a white > dial-face. > > As I said, my first dial had a white dial-face. After that, I switched to > brown, which was a big improvement in usability. > > I suggest brown instead of white. > > Someone implied that, the more contrast (between light and shadow), the > better. Not so, when the dial-face is too white to look at in bright > sunlight. > > As for gray: Gray reflects the visible wavelengths in a relatively equal > mix, resulting in no perceived hue. If some hues are (at least relatively) > to be avoided, then obviously gray isn't what you want. > > At each end of the visible spectrum, there is, of course, radiation that > isn't visible. > Infrared (IR) and ultraviolet (UV). > > One possible disadvantage of that is that, when you don't perceive it or > its intensity, then of course you could conceivably get a dangerous amount > (accutely or cumulatively) without any perception of it. > > For example, never look at the sun when, due to a haze, or due to the sun > being low in the sky, the sun doesn't look bright. You don't have any > perception of how ingtense the UV or IR is. It could burn your eye without > any feeling of discomfort. (I don't know which of those is more dangerous, > but there have been official warnings to never look at the sun when it > seems less bright due to haze or low altitude.) > > Aside from that, there's been evidence that, when people spend a lot of > time outdoors, in bright sunny climate, then many years of exposure to the > bright blue light can cause some long-term cumulative damage. So maybe blue > isn't the most desirable hue. > > Yellow, beings the complement of blue, looks yellow because it absorbs > blue, removes blue from the light that it reflects. > > Also, yellow isn't particularly close to either end of the visible > spectrum. > > Brown is defined as: > > "Any of a group of colors between red and yellow in hue, of medium to low > brilliance, and of moderate to low saturation." > > Then, dark brown would be brown with particularly low brilliance--a > desirable attribute for a sundial-face. Might that be the best color for a > dial-face? > > Tan is defined as: > > "Light yellowish brown." > > ...suggesting more brilliance than brown (but surely a lot less than > white), and enough saturation to be perceived as yellow, which seems a good > thing. > > Brown, especially dark brown, or maybe t
Re: Sundial Puzzle Corner
Shadow will be longest to the north at midnight, twice a year, at any point north of the Arctic Circle. John Lynes On 28 October 2016 at 07:58, Frank King <f...@cl.cam.ac.uk> wrote: > > > Where on the planet would you have to > be, and at what time of year, for these > instructions to give the correct result? > > --- https://lists.uni-koeln.de/mailman/listinfo/sundial
Re: Terms to describe markings on dials (or other objects)
Depressed? John Lynes On 27 October 2016 at 23:12, John Pickard <john.pick...@bigpond.com> wrote: > Good morning, > > As part of my research on wire strainers (tools used to tighten wire in > fences) I am struggling with trying to find some generic terms to describe > the markings (patent numbers, part numbers and other information) on the > tools. > > > John Pickard > john.pick...@bigpond.com --- https://lists.uni-koeln.de/mailman/listinfo/sundial
Fwd: Using color temperature to determine time
I'm afraid Dan Uza's proposal is a non-starter. The colour temperature of daylight fluctuates, depending on the weather. Even on a cloudless day it is obvious that the colour of the sky varies from point to point. The colour temperature is low near the horizon and highest in the direction facing away from the sun and at an altitude roughly equal to (90 degrees minus the solar altitude). These patterns are clearly visible to the naked eye. John Lynes On 29 August 2016 at 13:37, Dan-George Uza <cerculdest...@gmail.com> wrote: > Hello! > > I've recently become interested in film photography. I think it has some > similarities to sundials. For example, it is said that black and white film > photography is about taking pictures not of actual subjects, but of light > and shadows. I find it fascinating how light actually darkens the salts on > the photographic material, like a gnomon does to the surface of a sundial. > Not to mention the meridian lines in churches that also act like giant > camera obscuras, projecting the solar disc image onto the pavement. > > Now I've read that daylight color temperature fluctuates by the hour of > the day: light in the early morning and late evening has under 5000 K, > while around noon it reaches 6000 K and beyond . But can you actually use > this intrinsic light quality for time telling i.e. design a color > temperature sundial? > > Dan Uza > Romania > > --- > https://lists.uni-koeln.de/mailman/listinfo/sundial > > > --- https://lists.uni-koeln.de/mailman/listinfo/sundial
Re: Using analemmatic sundials for determining sun exposure times
My guess would be a north-facing wall on the Arctic Circle at the summer solstice, or a south-facing wall on the Antarctic circle at the summer solstice down under. John Lynes On 14 June 2016 at 16:39, Frank King <f...@cl.cam.ac.uk> wrote: > Dear Willy and Geoff, > > Good answers but the correct value > exceeds both your scores. > > Let's see who else will rise to the > challenge before I declare my hand! > > Frank > > --- > https://lists.uni-koeln.de/mailman/listinfo/sundial > > --- https://lists.uni-koeln.de/mailman/listinfo/sundial
Re: Gnomonics and building code
UK practice distinguishes between the requirements for new buildings and the protection of sunlight access for existing buildings. New dwellings, or non-domestic buildings which have a particular requirement for sunlight, are considered reasonably sunlit provided that - - at least one main window faces within 90 degrees of due south; and - the centre (on the inside face of the window wall) of at least one window to a main living room can receive at least 25 per cent of annual probable sunlight hours, including at least 5 per cent of annual probable sunlight hours in the winter months between 21 September and 21 March. Note the insistence on probable sunlight hours. This is the long-term average of the total number of hours during a year in which direct sunlight reaches unobstructed ground, when clouds are taken into account. In an existing dwelling, if a living room of an existing dwelling has a main window facing within 90 degrees of due south, and any part of a new development subtends an angle of more than 25 degrees to the horizontal measured from the centre of the window in a vertical section perpendicular to the window, the sunlighting of the existing dwelling may be adversely affected. This will be the case if the centre of the window - receives less than 25 per cent of annual probable sunlight hours, or less than 5 per cent of annual sunlight hours between 21 September and 21 March, and - receives less than 0.8 times the former sunlight hours during either period, and - has a reduction in sunlight received over the whole year greater than 4 per cent of annual probable sunlight hours. Protection is also required for sunlight in existing gardens or play areas. The centre of the space should receive at least 2 hours of sunlight on 21 March. Alternatively at least half the area should receive at least 2 hours of sunlight on 21 March. There is lots more small print, but these are the principal provisions. I hope you will share your eventual conclusions with the sundial mailing list. John Lynes On 3 June 2014 12:09, ml...@interia.pl wrote: Dear Diallists, I’m currently preparing a paper on Polish building code regulations in relation to provision of sunlight in apartments, and would like to include a chapter on similar regulations in the other countries. In general, we have a building code requirement to provide at least 3 hours of sunlight in at least one room in any type of apartment, between 7:00 and 17:00 on the days of equinox. In the dense urban areas (specified in local zoning plans or by administrative decisions when there is no zoning plan) the requirement can be limited to at least 1,5 hour of sunlight, between 7:00 and 17:00, for at least one room in multi-room apartments, while one-room apartments (studio) can have no sunlight. It has to be noted that within the time range given by the building code (that is between 7:00-17:00), it is allowed to sum up separate intervals of sunlight. The original intention of setting this time range was to not take into consideration the first and last hour of the day, due to low energetic levels of the sunlight and low angles of incident sunlight. The idea of providing sunlight in apartments has a long history of course, but it was first so explicitly manifested during Congress of Modern Architecture CIAM in Athens in 1933, where requirement of providing at least 2-hours of sunlight for every apartment during winter solstice was included in the conference document - Athens Charter, manifesto of modern movement in architecture. Polish regulations in this subject come from Russia. To my knowledge they were first introduced in Russia as sanitary regulations in 1963 and in subsequent decades adopted in other countries of the former Soviet block, but since the collapse of the communism they have evolved separately and different ways and now they differ quite significantly – but I don’t know many details unfortunately. If You have ever had contact with similar general building code legislation requirements in Your countries or local law (zoning plan etc.), I would be indebted if You could share with me its specific requirements. The goal of the planned paper is to formulate guidelines for optimizing existing building code in Poland, as it is not fully clear in details and as a result it poses many interpretation problems to architects as well dwellers who wish to verify if the apartment was designed and implemented according to building code regulations. Regards, Maciek Lose --- https://lists.uni-koeln.de/mailman/listinfo/sundial --- https://lists.uni-koeln.de/mailman/listinfo/sundial
Re: Design of Cards for Campbell Stokes Sunshine Recorder
There's a very full and well-illustrated description of the Campbell Stokes sunshine recorder, with a reproduction of the equinoctial card in Handbook of Meteorological Instruments, HMSO 1956, reprinted 1961. This tells us, inter alia, that the cards are made from good quality paste board, not ordinary paper. The Meteorological Office specification lays down that their length must not change by more than 0.01 inch after immersion in water for 18 hours, and must not contract by more than 1 per cent on redrying. John Lynes On 19 April 2014 00:27, Brooke Clarke bro...@pacific.net wrote: Hi: I just got one of the Campbell Stokes Sunshine Recorders but it came without any of the cards. I'd like to make cards for Winter, Equinox and Summer seasons. Is there any information about doing that available It appears that each of them has a different width probably so you use the correct card in the correct slot. Winter: 38mm, Equinox: 42 mm, Summer: 33mm http://www.prc68.com/I/CampbellStokes.html -- Have Fun, Brooke Clarke http://www.PRC68.com http://www.end2partygovernment.com/2012Issues.html --- https://lists.uni-koeln.de/mailman/listinfo/sundial --- https://lists.uni-koeln.de/mailman/listinfo/sundial
Re: Meridian in Siena, Florence
Roger Bailey was nearly right first time! Egnazio Danti planned and partly constructed two meridians inside the Church of Santa Maria Novella, Florence. One gnomonic aperture (recently restored) was drilled through the rose window in the south-facing facade. The second penetrated the top of the same facade. Danti was expelled from Florence before these meridians could be brought into regular use. John Lynes From: Roger Bailey rtbai...@telus.net To: sundial@uni-koeln.de Sent: Sunday, 6 May 2012, 5:12 Subject: Re: Meridian in Siena, Florence I confused the Santa Maria churches in Florence. The Dante sundials are on the south facing facade of Santa Maria Novella. Click on http://www.waymarking.com/waymarks/WM9EGY_Danti_Sundials_at_Santa_Maria_Novella_Florence_Italy The famous meridian is in Santa Maria del Fiore. These are all great instruments to help reset the calendar but there are too many Santa Maria churches. Regards, Roger Bailey From: Roger Bailey Sent: Friday, May 04, 2012 7:51 PM To: Jos Kint ; sundial@uni-koeln.de ; Richard Subject: Re: Meridian in Siena, Florence There are also some great sundials on the south facing facade of S.Maria del Fiore church in Firenze (Florence). As usual the devil is in the detail; these are significant sundials overlooked by most tourists, as significant as the famous meridian in the church. Here are an equatorial ring evoking the brass equatorial ring of Ptolemy in the Great Hall in Alexandria and a pair of quadrants facing east and west, recently restored. The scientific basis for the calendar reforms was established here, with these sundials and the meridian. Regards, Roger Bailey From: Jos Kint Sent: Friday, May 04, 2012 2:13 PM To: sundial@uni-koeln.de ; Richard Subject: Re: Meridian in Siena, Florence Dear Richard, In the S.Maria del Fiore church in Firenze you can see the largest sundial in a church, constructed in 1467 by P. Toscanelli. The gnomon is a hole 90,11 meters high. According to the British historian-astronomer J.L. Heilbron it was devised to check whether the inclination of the earth's axis changed over time. For more details: read the remarkable book of Heilbron: The sun in the church. Jos Kint 50°59'N 3°39'E - Original Message - From: Richard To: sundial@uni-koeln.de Sent: Friday, May 04, 2012 8:36 PM Subject: Meridian in Siena, Florence It has been a privilege to learn from the information on this site for many years. Now, looking forward to a trip to Florence and Siena, Italy, it would be very meaningful to have your recommendations. Is there an outstanding meridian to view in Siena: where is it, and is it open for public viewing. Would individuals there be aware of it? What are the directions for it's location? Similarly, would there be one top meridian to view in Florence, with the same questions posed for Siena. Thank you for your help. Richard D. Swensen One of life's great gifts was the extra-ordinary design of the Richard D Swensen sundial,( at that time the largest, most accurate vertical face sundial) by Dr. John P.G.Sheperd at my retirement .www.uwrf.edu/AboutUs/RichardSwensenSundial.cfm --- https://lists.uni-koeln.de/mailman/listinfo/sundial --- https://lists.uni-koeln.de/mailman/listinfo/sundial --- https://lists.uni-koeln.de/mailman/listinfo/sundial --- https://lists.uni-koeln.de/mailman/listinfo/sundial --- https://lists.uni-koeln.de/mailman/listinfo/sundial
Re: Meridian in Siena, Florence
I'd strongly recommend a book mainly on the Florence meridians: The Line of the Sun, edited by Filippo Camerota, Edizioni della Meridiana, Florence, 2007. You can buy a copy in the Florence Museum of the History of Science. See http://brunelleschi.imss.fi.it/meridiane/ You'll find an account of a meridian line in Siena in The Sun in the Church by J L Heilbron, Harvard, 1999. I spent two hectic days in Florence last week. In Florence Cathedral tourists were confined to the nave, so were denied access to Toscanelli's famous meridian in the north transept. The attendants eventually let me through to photograph the meridian, so it's worth persisting. I wasn't able to discover the 13th century sundial on the Ponte Vecchio. I hope you have better luck! John Lynes From: Richard ghswen...@aol.com To: sundial@uni-koeln.de Sent: Friday, 4 May 2012, 19:36 Subject: Meridian in Siena, Florence It has been a privilege to learn from the information on this site for many years. Now, looking forward to a trip to Florence and Siena, Italy, it would be very meaningful to have your recommendations. Is there an outstanding meridian to view in Siena: where is it, and is it open for public viewing. Would individuals there be aware of it? What are the directions for it's location? Similarly, would there be one top meridian to view in Florence, with the same questions posed for Siena. Thank you for your help. Richard D. Swensen One of life's great gifts was the extra-ordinary design of the Richard D Swensen sundial,( at that time the largest, most accurate vertical face sundial) by Dr. John P.G.Sheperd at my retirement .www.uwrf.edu/AboutUs/RichardSwensenSundial.cfm --- https://lists.uni-koeln.de/mailman/listinfo/sundial --- https://lists.uni-koeln.de/mailman/listinfo/sundial
Re: Shadow caster
Dave Bell - The trouble with your double glazing is that it is no longer effectively sealed. Moisture is entering from the interior of your building, and condensing on the inside surface of the outer face. The remedy is to ventilate the gap in the double glazing to the exterior, so that the relative humidity in the gap is the same as the relative humidity in the outdoor air. Block the passage with gauze to prevent the entry of insects or dirt. The double glazing should then become clear. Its thermal insulation would barely be affected. Worth trying? John Lynes From: Dave Bell db...@thebells.net To: 'Reinhold Kriegler' reinhold.krieg...@gmx.de Cc: sundial@uni-koeln.de Sent: Sunday, 4 March 2012, 20:33 Subject: RE: Shadow caster I agree that a bright sun spot would be nice, but I don’t want to black out much of the window. Unfortunately, over the years, the double-glazed window has grown a spotty diffusing layer of something (mold? dried rainwater seepage?) that makes it less than ideally clear. I tried a solid, 2 inch spot of aluminum foil, and the shadow is barely visibly 8 feet from the glass. I don’t think the glazing is something I can disassemble for internal cleaning… I’ll print some positive and negative zone plates in different sizes this week, and see how they work. Dave From:Reinhold Kriegler [mailto:reinhold.krieg...@gmx.de] Sent: Sunday, March 04, 2012 11:51 AM To: 'Dave Bell' Subject: AW: Shadow caster ☺ I thought so!!! Actually: Inside the house a little sunspot is much more fun than a tiny dizzy and diffuse shadow point… Reinhold * ** *** * ** *** Reinhold R. Kriegler Lat. 53° 6' 52,6 Nord; Long. 8° 53' 52,3 Ost; 48 m ü. N.N. GMT +1 (DST +2) www.ta-dip.de http://de.youtube.com/watch?v=XyCoJHwzzjUfmt=18 http://www.ta-dip.de/dies-und-das/r-e-i-n-h-o-l-d.html http://www.ta-dip.de/dies-und-das.html -Ursprüngliche Nachricht- Von: Dave Bell [mailto:db...@thebells.net] Gesendet: Sonntag, 4. März 2012 20:35 An: ' Reinhold Kriegler ' Betreff: RE: Shadow caster Yes, I remember John’s work well, particularly for gnomon points, so the shadow isn’t truncated. I was thinking about putting a shadow spot on one of my living room roof windows, particularly with the approaching Equinox. But over an 8 to 15 foot throw, the shadow would be fairly diffuse. I’m going to try printing some large (1 to 3 inch outside diameter) zone plates on transparency film, and see how they work… From:Reinhold Kriegler [mailto:reinhold.krieg...@gmx.de] Sent: Sunday, March 04, 2012 10:05 AM To: 'David Bell'; sundial@uni-koeln.de Subject: AW: Shadow caster John Carmichaelhas done excellent research work about this question! Just contact him! Regards! Reinhold Kriegler * ** *** * ** *** Reinhold R. Kriegler Lat. 53° 6' 52,6 Nord; Long. 8° 53' 52,3 Ost; 48 m ü. N.N. GMT +1 (DST +2) www.ta-dip.de http://de.youtube.com/watch?v=XyCoJHwzzjUfmt=18 http://www.ta-dip.de/dies-und-das/r-e-i-n-h-o-l-d.html http://www.ta-dip.de/dies-und-das.html -Ursprüngliche Nachricht- Von: sundial-boun...@uni-koeln.de [mailto:sundial-boun...@uni-koeln.de] Im Auftrag von David Bell Gesendet: Sonntag, 4. März 2012 18:50 An: sundial@uni-koeln.de Betreff: Shadow caster Several times, there have been discussions about how to improve the shadow cast by a point nodus. I partially recall some conclusions regarding the optimum diameter vs, throw length, and some thoughts about adding an annular ring to take advantage of diffraction. Can anyone help remind me? Thanks! Dave Sent from my iPhone --- https://lists.uni-koeln.de/mailman/listinfo/sundial --- https://lists.uni-koeln.de/mailman/listinfo/sundial --- https://lists.uni-koeln.de/mailman/listinfo/sundial
Re: Walking Shadow Riddle
Here's my guess: If, as you suggest, you start at dawn on the equinox and on the equator you will walk east for six hours before noon and west for six hours before sunset, finishing at the point where you started. If you start at the north pole at the equinox you will move in a spiral, crossing each longitude once every 24 hours. John Lynes From: John Carmichael jlcarmich...@comcast.net To: 'Sundial List' sundial@uni-koeln.de Sent: Tuesday, 6 September 2011, 19:08 Subject: Walking Shadow Riddle A Riddle: I was watching a dumb movie last weekend and there was a bit of dialogue that caught my attention. I’m sure this relates to sundials and mapping, but the answer eludes me. One of the characters was told by the wise man to: “walk towards your shadow all day, starting at sunrise and stopping at sunset” at which point the walker would discover the location of a treasure. So I asked myself, what would the path of the trek look like on a map? But I can’t figure it out. This is as far as I get in my thinking: I started considering an example with these conditions.- The walk begins at dawn on the equinox, and the man is on the equator. And the walk ends at sunset. So we know that the walk will last twelve hours. If the average speed of a walking man is 5 km/hr. , it is 12 hours from sunrise to sunset; then we know that he will walk 60 km. He’ll start walking towards the west at dawn and his path will turn towards the north in the morning as the sun heads south. After Solar Noon, his path will turn towards the east he’ll end up facing due east at sunset. And we know that the path will be a curve since his shadow will always be changing direction. But what would the curve look like on a map? Would it be a hyperbola? How would the curve change if he walks on the summer solstice instead? What if he’s at the North Pole? John C. --- https://lists.uni-koeln.de/mailman/listinfo/sundial --- https://lists.uni-koeln.de/mailman/listinfo/sundial
Re: special events
Dear Frank, Your story reminds me of Eratosthenes, the father of geography. He invented latitude and longitude and, in about 250 BCE, measured the circumference of the earth. Eratosthenes had heard that at noon at the summer solstice at Syene (present-day Aswan) in Southern Egypt you could look down a deep well and see a reflection of the sun. Eratosthenes, who lived in Alexandria, measured the shadow of a local obelisk when the shadow was shortest. Knowing that it took a camel fifty days to travel from Syene to Alexandria, he was able to deduce the circumference of the earth. Aswan is actually about forty miles north of the Tropic, and is not precisely on the same meridian as Alexandria. Still, like you, Eratosthenes was a genius! John Lynes Dear Jackie, You are right... I seem to remember hearing about a sun well ... The sun only shone right down it at midday when it was directly overhead. I once made a hunt-the-sub-solar-point trip to Hong Kong. I had been invited to give a course of lectures but I insisted on visiting at a time of year when the solar declination suited my ulterior motive! I also visited a friend who was chief engineer on a site where a massive pumping station was being built in a deep-water reservoir. At this stage the structure consisted of six huge vertical tubes, perhaps 3m in diameter and standing 40m high. When you looked down a tube you could normally see nothing beyond the top few metres. This site was five miles north of where I wanted to be but the sun's altitude would still be about 89 deg. 55'. While I was hunting the true sub-solar point my friend called the entire work-force together and told them all to look down these tubes. Spot on cue, the sun shone down the tubes and for a minute or so there was a blinding reflection from the pools of water at the bottoms of the tubes. Fast forward 10 years and I met another structural engineer at a wedding reception and he told me that he had worked on a number of projects in Hong Kong. It then turned out he had worked on this pumping station. One incident he remembered clearly... One day when it was fearfully hot, the chief engineer called everyone on site together and told us all that he had a mad friend who had calculated when the sun would shine directly down the tubes. We all had to lean over and look down and, sure enough, the holes suddenly went from deeply gloomy to blindingly bright. Hmmm. You never know where an understanding of the ways of the sun might lead you! All the best FrankFrom: Frank King frank.k...@cl.cam.ac.uk To: Jackie Jones jac...@waitrose.com Cc: 'Sundial List' sund...@rrz.uni-koeln.de Sent: Thursday, 28 July 2011, 10:51 Subject: Re: special events --- https://lists.uni-koeln.de/mailman/listinfo/sundial
Re: special events
Wandering further off topic ... In my time as a university lecturer I used to train architectural students to pace a metre accurately. It's a skill worth acquiring, as it can save loads of time in quick surveying. I was know as Mister Metre for the accuracy of my stride, but was never (I hope) called a slave-driver. I also encouraged students to note the height of their belly-button in relation to a metre rule. They could then mark the height of a vertical wall with reasonable confidence. John Lynes From: Tony Moss t...@lindisun.demon.co.uk To: sundial@uni-koeln.de Sent: Thursday, 28 July 2011, 18:04 Subject: Re: special events Fellow SML readers, I recall reading somewhere that special measuring individuals - probably slaves - had their stride length set by a length of chain which would work very well if the surface was reasonably flat...or did I dream it? Tony Moss --- https://lists.uni-koeln.de/mailman/listinfo/sundial
Advice wanted, on 'Analemmatic' sundial orientation
I'm grateful for the generous reception you gave to my last contribution to this thread. Here belatedly is another possible solution, less impractical but more complex than my last effort. Imagine a North-South meridian line on flat ground. On this line place a thin flat vertical mirror - essentially a vertical reflective slit - a few feet above the ground and pivoted to rotate about a vertical axis through the mirror and the meridian. When the sun shines, a visitor is asked to turn the mirrored slit so that the sun's reflection falls along the meridian line. Straight below the slit, locked to the same vertical axis, is a small horizontal analemmatic sundial, a few inches across, placed so that the axis of rotation of the assembly coincides with the calendar date-point on the analemmatic dial, and the major axis of the analemmatic dial's ellipse is parallel to the plane of the mirror. The direction of the meridian line indicates the solar time on the (modified, see below) face of the analemmatic dial. The azimuth of the mirror, measured from the meridian, would be only half the azimuth of the sun, so the hour markings on the analemmatic dial would need adjusting, e.g. the 1pm mark would be relabelled 2pm (sorry, 10.am). They would run anti-clockwise, and would of course be reversed from north to south. A groundsman would have to keep the mirror polished, and realign the date-point with the axis of rotation perhaps once a week. He might fix a different dial for daylight saving. Now comes the nifty bit! Mr Phillips is not forced to accept a North-South meridian line. He could commission a line parallel to his main driveway, for aligning the reflection of the sun. A small fixed North-South marker would still indicate the time on the analemmatic dial. I leave it to the heavyweights to recalculate the hourly markings on the dial face. Alas the gnomon is no longer human, but the device would be interactive, instructive and, I daresay, unprecedented. Apologies for a disgracefully late entry! John Lynes -Original Message-From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] Dear Sundial Experts, I have recently joined this Mailing List, and hope that any members will be able to give me some assistance on the following situation. Our local Stately Home (Kentwell Hall, Long Melford, Suffolk) is considering installing an Analemmatic sundial, as a new interactive attraction 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 the acknowledged 'experts' for these features), who have told us that its central scale of dates must be aligned North/South - plus that hour 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. BecauseKentwell 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 thatall 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
RE: Great Circle Calculations
Any map drawn in gnomonic projection has the property that all great circles
are straight lines. To plot a great circle on such a map, just draw a straight
line from your departure point to your destination.
Any book on map projections will tell you about the gnomonic projection, but
you will already be familiar with it: a flat sundial is essentially a gnomonic
projection of the sky hemisphere.
John Lynes
Lat 51 deg. Long 0 deg.
John Carmichael [EMAIL PROTECTED] wrote:
st1\:*{behavior:url(#default#ieooui) } It would be
useful if there were an easy-to-use website that would produce a map that would
show the Great Circle route between any two points on a map. You would just
enter the two points in latitude and longitude then it would produce a map. It
would be helpful if it would also give you compass headings at any point along
the route. Does anybody know if such a website exists?
John
---
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sundial motto for clergy
Sorry I can't remember where this one comes from: Lux dei vitae viam monstrat Sed umbra horam atque fidem docet (The light of God showeth the way of life, But the shadow both telleth the hour and teacheth the faith). John Lynes P.O.Box 126, Hebron, West Bank, Israel/Palestine. -
