Re: Why the clock rotates clockwise?
It's often claimed that the fore-runners of mechanical clocks were physical models of the heavenly sphere(s). In the northern hemisphere this/these appeared to rotate clockwise. So clocks followed suit. John Lynes - Original Message - From: Sumi Yoichi [EMAIL PROTECTED] To: sundial@rrz.uni-koeln.de Sent: Friday, June 14, 2002 2:42 PM Subject: Why the clock rotates clockwise? Sundialists I want to ask a simple question to sundialists in the ML. Why the clock rotates clockwise? Most Japanese horologist says as follows. In the very old times, primitive people knew the rough time from the sun-shadow of the vertical gnomon on the ground. In that case, the shadow of the gnomon rotates clockwise on the north hemisphere, so the clockwise-rotating mechanical clock was made. This is right? Sundialists know well the shadow of the gnomon of the vertical type sundial on the wall rotates anticlockwise. I think the way of looking at the clock is very like the vertical sundial on the wall. Why the clock maker did not make the anticlockwise-clock? Can anyone know the article or the web-site in English dealing with my question? Thanks in advance Sumi Yoichi Japan [EMAIL PROTECTED] http://www.spi.ne.jp/~gnomon/ - -
Re: Seasonal Sunrise Marker
Extending Roger Bailey's treatment, if you know the time and direction of sunrise you can easily estimate the time and direction of sunset, or vice-versa: Time of sunset = 24 - (time of sunrise) Azimuths of sunrise and sunset are equidistant from the North-South meridian, remembering that sunrise is east and sunset west of the meridian. If you know the direction of sunrise or sunset at a given solar declination D degrees North, you can easily estimate the time and direction of sunset or sunrise at declination D degrees South: Time of sunrise at D degrees South = 24 - (time of sunset at D degrees North) Azimuths of sunrise at D degrees South and sunset at D degrees North are equidistant from the East-West line, remembering that in the Northern hemisphere the former is South and the latter North of the East-West line. You can interchange sunrise and sunset in these expressions. If you have a vertical declining sundial with declination lines and a horizon line, you have all the data you need to use the above information. John Lynes Roger Bailey wrote - The times of sunrise and sunset can be easily determined on a vertical declining dial that has declination lines. The horizontal line from the base of the gnomon is the horizon line. The intersection of the declination line and the horizon line shows the time of sunrise or set. This is of limited use on south facing dials as the scale of the gnomon and resulting declination lines is usually to great to show much more than the winter solstice.
Re: Seasonal Sunrise Marker
Two words were carelessly omitted from the third paragraph of my last posting. Please accept my apologies. It's hard enough to digest even when the wording is correct! Below is a corrected version of the posting:- Extending Roger Bailey's treatment, if you know the time and direction of sunrise you can easily estimate the time and direction of sunset, or vice-versa: Time of sunset = 24 - (time of sunrise) Azimuths of sunrise and sunset are equidistant from the North-South meridian, remembering that sunrise is east and sunset west of the meridian. If you know the time and direction of sunrise or sunset at a given solar declination D degrees North, you can easily estimate the time and direction of sunset or sunrise at declination D degrees South: Time of sunrise at D degrees South = 24 - (time of sunset at D degrees North) Azimuths of sunrise at D degrees South and sunset at D degrees North are equidistant from the East-West line, remembering that in the Northern hemisphere the former is South and the latter North of the East-West line. You can interchange sunrise and sunset in these expressions. If you have a vertical declining sundial with declination lines and a horizon line, you have all the data you need to use the above information. John Lynes Roger Bailey wrote - The times of sunrise and sunset can be easily determined on a vertical declining dial that has declination lines. The horizontal line from the base of the gnomon is the horizon line. The intersection of the declination line and the horizon line shows the time of sunrise or set. This is of limited use on south facing dials as the scale of the gnomon and resulting declination lines is usually to great to show much more than the winter solstice.
Re: Polar ceiling sundial
Thanks, Fer. Apologies all round, and especially to Anselmo. I now think his proposal would work after all. But only in the winter months. At noon at the equinox the reflected beam would be vertically above the mirror. During the summer months the beam would be reflected south of the east-west line, i.e. back through the window. Or am I wrong again? John Lynes Fer de Vries wrote - The idea by Anselmois correct. The mirror is just between the polar axis and the horizontal ceilng and by this the pattern on the ceiling looks like apolar dial.
Ceiling Sundial
In response to both Dave Bell and John Carmichael, I took the small mirror as fixed, and required it only to be flat and, of course, stable. These are necessary conditions for any ceiling sundial. My proposal does not require any knowledge of the actual alignment of the mirror. John Carmichael is certainly correct in noting that very slight errors in placing transparencies and lasers would cause large errors on the ceiling. That's life! But uncertainty in the actual alignment of the mirror would not be a source of error. Nor would an uneven, sloping or vaulted ceiling. John Carmichael's final paragraph is dead right, but it would take months and still needs a reasonably flat ceiling. John Lynes
Ceiling Sundial
Here's a simpler proposal. Transfer the declination lines and hour lines of a horizontal sundial onto a transparent sheet. Mark a small circle on the centre of the mirror. Support the horizontal transparent sheet, rotated from north to south, with its nodusvertically above the centre of the circle, at a distance equal to the height of the transparent sundial's gnomon. Project a laser beam through the transparent sheet onto the centre of the circle. Make sure the beam passes through the sundial scale at a point corresponding to some chosen time and date. The reflected spot on the ceiling is the appropriate point on the ceiling sundial. Repeat for other dates and times. John Lynes
Re: Ceiling Sundial
Here's an alternative approach, which would work best with two people: Set up a simple horizontal sundial, with declination lines, correctly oriented, beside the mirror, say a foot to one side. Using a laser pointer, or just a bare low-voltage filament lamp, cast a shadow of the gnomon onto the sundial scale at some chosen hour and declination. Move the laser pointer exactly one foot sideways to illuminate the centre of the mirror. Mark the position of the spot of light reflected onto the ceiling. This is the point on the ceiling sundial for the chosen hour and declination. Repeat for other hours and declinations. Note that this does not assume that the mirror is horizontal. Obviously the method could be simplified if declination lines are not wanted on the ceiling. Happy New Year! John Lynes
Re: Shadow casting program
Since nobody seems to have offered a reply to Albert's request for a program to show shadows cast by buildings, may I offer a simple suggestion? Use any perspective drawing program. Arrange the viewpoint to be at a large distance from the building, and in a direction corresponding to the altitude and bearing of the sun at whatever time and date you choose. Then any surface that is visible in your perspective drawing will be sunlit. Any hidden areas will be in shadow. A shadow is simply a space which the sun doesn't see. Repeat the process for other times and dates. But surely a sundial enthusiast would prefer to use a physical model of the building, with a low-voltage lamp to simulate the sun and a sundial to show the hour and declination corresponding to the sun's direction. John Lynes -Original Message-From: A.Brown [EMAIL PROTECTED]To: sundial list sundial@rrz.uni-koeln.deDate: 29 December 2001 22:55Subject: Shadow casting prog Would anyone know if there is a user friendly public domain program to show the shadows cast by buildings (or objects) at a given location for various dates. Ideally with animation although sequential imagescould be dropped into other programs. Easy recalculation with various building heights would be an added bonus. TIA Albert
BSS Bulletin. Southern Hemisphere Sundial?
Well spotted!My guess would be horizontal, southern hemisphere.If vertical south-facing the Roman numerals would be upside down seen frombelow.John Lynes
Re: Transalpine hours
-Original Message-From: John Davis [EMAIL PROTECTED]To: sundial@rrz.uni-koeln.de sundial@rrz.uni-koeln.deDate: 02 August 2000 08:54Subject: Transalpine hours Hi all, I've come across a reference to transalpine hours in Heilbron's excellent The Sun in the Church (pg 66). This is a term which escaped me when I was compiling the BSS Glossary. Can someone supply a definition, please. Regards, John --- Dr J R DavisFlowton, UK52.08N, 1.043Eemail: [EMAIL PROTECTED] The term Transalpine Hours (hora oltramontana, I think) was used in Italy to describe the time-keeping system prevailing in Northern Europe, with noon at 12 o'clock, as distinct from Italian hours, reckoned from sunset. There is an example on the sundial on the facade of the church of Santa Maria Novella in Florence. Interestingly, there is an English word ultramontane (literally transalpine) which means excessively loyal to the papacy. So it seems to be a term of disapproval, its precise significance depending on which side of the Alps you live. Regards - John Lynes 4 Aigburth Avenue, St Georges Road, Hull HU3 3QA, England.
