Equinoctial vs. Equatorial
Hello, After posting a picture of a dial to the list which was shown in a horizontal attitude instead of being on an angled base as it should have been, I have a broader question to ask. What is the real difference between a dial described as equinoctial and one described as equatorial, and why would one term be chosen over the other to describe a sundial? Best, Jim Tallman www.artisanindustrials.com http://www.artisanindustrials.com/ jtall...@artisanindustrials.com --- https://lists.uni-koeln.de/mailman/listinfo/sundial
Re: How would this sundial work?
There is more of a description of that dial at http://www.diduknow.info/sun/san6.html#. It is a horizontal dial of which the gnomon has been broken off. It is for use during daytime and at night. I presume the rotating plate allows adjustment for telling time by the moon, depending where the moon is in its ~30 day synodic period. -Bill On Tue, Feb 14, 2012 at 9:25 AM, J. Tallman jtall...@artisanindustrials.com wrote: Hello All, ** ** I came across a picture of a sundial this morning that I found to be confusing. See the dial picture on the following web page – it has a vertical post gnomon and the dial plate looks like it might be designed to rotate about the center: ** ** http://www.diduknow.info/sun/san5.html# ** ** Have any of you seen this dial before and do you have any ideas how it might work? ** ** ** ** Best, ** ** Jim Tallman www.artisanindustrials.com jtall...@artisanindustrials.com ** ** --- https://lists.uni-koeln.de/mailman/listinfo/sundial --- https://lists.uni-koeln.de/mailman/listinfo/sundial
Re: Equinoctial vs. Equatorial
Tony’s explanation is also my understanding of the definitions – but then Tony and I do talk to each other quite a lot! Mike Shaw 53º 22'N 03º02'W www.wiz.to/sundials - No virus found in this message. Checked by AVG - www.avg.com Version: 2012.0.1913 / Virus Database: 2112/4809 - Release Date: 02/14/12 --- https://lists.uni-koeln.de/mailman/listinfo/sundial
Re: Equinoctial vs. Equatorial
I think this is the answer: Until the Middle Ages the time was shown in a distribution of 12 hours between sunrise and sunset. Since the duration of one hour in that measuring system is different depending on the season this hours are named unequal hours. Sundials where showing these unequal hours. Later a day (day and night) was divided into 24 equal hours regardless of the seasons. The length of an equal hour was similar to that of an unequal hour during the equinoxes. Therefore the name of equal hours was also named equinoxiale hours. A sundial showing these equinoxial hours was named an equinoxial sundial. So all the sundials since the modification of unequal hours in equal hours. An equatorial sundial shows the time in a plane which is parallel to the equator plane. This can be on a flat surface or on a cylindrical band which is located in that plane as it is the case in an armirally sphere. Willy Leenders Hasselt in Flanders (Belgium) Visit my website about the sundials in the province of Limburg (Flanders) with a section 'worth knowing about sundials' (mostly in Dutch): http://www.wijzerweb.be Op 14-feb-2012, om 15:49 heeft J. Tallman het volgende geschreven: Hello, After posting a picture of a dial to the list which was shown in a horizontal attitude instead of being on an angled base as it should have been, I have a broader question to ask. What is the real difference between a dial described as “equinoctial” and one described as “equatorial”, and why would one term be chosen over the other to describe a sundial? Best, Jim Tallman www.artisanindustrials.com jtall...@artisanindustrials.com --- https://lists.uni-koeln.de/mailman/listinfo/sundial --- https://lists.uni-koeln.de/mailman/listinfo/sundial
Re: Equinoctial vs. Equatorial
In my precedent mail Sundials where showing these unequal hours. must be Sundials were showing these unequal hours. Willy Leenders Hasselt in Flanders (Belgium) Visit my website about the sundials in the province of Limburg (Flanders) with a section 'worth knowing about sundials' (mostly in Dutch): http://www.wijzerweb.be Op 14-feb-2012, om 21:08 heeft Willy Leenders het volgende geschreven: Sundials where showing these unequal hours. --- https://lists.uni-koeln.de/mailman/listinfo/sundial
RE: Equinoctial vs. Equatorial
I classify sundials into three principal categories-those that find time from the sun's hour angle; those that use the sun's azimuth; and those that use the sun's altitude-plus various combinations of two out of the three. In the first category, we generally subdivide dials according to the plane on which the shadow is projected-i.e., horizontal, vertical, equatorial, polar, etc. Sundials that project the sun's hour angle onto a plane parallel to the equator are equatorial dials. These include many forms such as the universal equatorial dial, the Augsburg-type dial, those with an armillary or crossed-Cs form, mechanical equatorial dials, and more. The convention in the US is to call all of these equatorial dials. In the United Kingdom, it is a convention to call them equinoctial dials. This is perhaps because the celestial equator is often called the equinoctial circle in the UK and the equinoctial circle/celestial equator are in the same plane as the terrestrial equator I prefer the label equatorial because it is a typology constructed in parallel to the others (horizontal, vertical, polar) which refer to an orientation on the earth and don't mix in celestial designations. Cheers, Sara Sara J. Schechner, Ph.D. David P. Wheatland Curator of the Collection of Historical Scientific Instruments Department of the History of Science, Harvard University Science Center 251c, 1 Oxford Street, Cambridge, MA 02138 Tel: 617-496-9542 | Fax: 617-496-5932 | sche...@fas.harvard.edumailto:sche...@fas.harvard.edu http://www.fas.harvard.edu/~hsdept/chsi.html --- https://lists.uni-koeln.de/mailman/listinfo/sundial
Georg of Peuerbach
I have been looking at the renaissance, the coming of age of science in general and sundial science in particular in Europe. The dark ages were just that, winter, a survival regime for intellectual thought and physical existence. With the renaissance things changed, like blossoms in the spring or the coming of age of people. I tend to view the world through a specific window, the prism of sundials. This gives a distorted but colorful view that avoids much of the noise in the general historical review and provides a unique perspective. Everything I need to know was learned through sundials Here my specific interest is the introduction of the polar gnomon. This innovation gave us sundials that were independent of the seasons and could be viewed from a distance, public instruments rather than private tools for timekeepers and astronomers. On a planar sundial with a polar gnomon, the shadows did not race off on tangents. Hour lines were constrained and visible on a dial face. In the Moslem world, by the 14th century, there was an a established science of astronomy, mathematics, instruments and sundials. In 1371 Al-Shatir most likely created the first planar sundial with a polar gnomon, almost as an aside, when he designed the complex sundial at the Great Mosque in Damascus . He and his predecessors established the mathematics and science that lead to this development. What did we have at that time in Europe? Rudimentary fumbling in Germany, an couple of experimental dials in Braunschweig, a rough rule from the Monastery at Erfurt defining the angles for a sundial irrespective of latitude and wall declination, a table of rudimentary design information passed on by rote. In Europe when did real sundial science start? Perhaps with Georg Peuerbach (1423-1461) in Austria. Google his name and follow the links. He is well known and respected by Austrians an intellectual force, the inventor of the ring and folding sundials, a skillful craftsman producing astrolabes and sundials and the designer of some of the first polar sundials in Europe. See http://www.regiomontanus.at/bild2_e.htm for the first folding sundial, a dial with a portable polar gnomon. or http://www.regiomontanus.at/bild2_e.htm the oldest sundial in Vienna. Was he the spark of the Renaissance in sundial science? As one indication, Peuerbach taught Regiomontanus. Knowledge advanced. Can you comment on my naive point of view or add more background on the pioneering work of Georg Peuerbach? Regards, Roger Bailey Walking Shadow Designs--- https://lists.uni-koeln.de/mailman/listinfo/sundial
