Hello Frank, As I understand you have a vertical dial at latitude phi = 55 deg, declining 30 deg to west. In other words: phi = 55 , i = 90 and d = 30 Calculating the style height v, the substyle distance b and the substyle hourangle ts I get: v = -29.78 b = -160.70 ( or 19.30) ts = 35.18 These are some different as you mention in your mail. You easily may calculate this with Zw2000.
v also is the equivalent latiude where the dial is an horizontal dial. This dial may be placed at latitude 90-29.78 = 60.22 deg as a vertical south facing dial as in your decription. The time offset of this dial is ts = 35.18 deg. So place the dial at 35.18 deg west, mount a WEB camera to it and read at your home your local time. Show the pictures on the WEB and we may enjoy it too..... Incline the dial with x extra degrees to use it at latitude 60.22 + x but leave it at 35.18 west. Happy dialing, Fer. Fer J. de Vries [EMAIL PROTECTED] http://www.iae.nl/users/ferdv/ Eindhoven, Netherlands lat. 51:30 N long. 5:30 E ----- Original Message ----- From: Frank Evans <[EMAIL PROTECTED]> To: <[email protected]> Sent: Saturday, March 24, 2001 10:20 PM Subject: trivial pursuit > Greetings, fellow dialists, > > Some fairly pointless thoughts and a question on vertical sundials. > > A south facing vertical sundial is fairly easily comprehended with its > symmetrical hour lines showing the time from six to six and its vertical > gnomon inclined to the wall at an angle of ninety degrees minus the > latitude so that a dial at the equator would have its gnomon horizontal > and one at the pole vertical. But there is a little subtlety in a south > facing dial and even more in a declining one. > > First, the six o'clock hour lines show sunrise and sunset only at the > equinoxes, when the sun rises and sets east-west. In the summer the > rising and setting points are behind the wall since the sun rises and > sets north of east-west and in the winter the sun rises later and sets > earlier than six. So in the winter, if those hour lines were not there > we would hardly miss them except for interpolation with the hours of 7 > am and 5 pm. > > With the south facing dial the hour lines are, as noted, symmetrically > grouped around twelve noon. But more fundamentally, they are also > symmetrically grouped around the gnomon. Fundamentally, because hour > lines are always grouped symmetrically around the gnomon, whether the > dial faces south or not. > > In a dial which does not face south the style or shadow edge of the > gnomon points (almost) to the pole star. The angle between the style > and the ground, if the style was long enough to reach the ground, is the > latitude. This angle is converted, or resolved, by dialists into two > angles known in the hermetic jargon of the fraternity as style height > and substyle distance. Presumably these terms descend to us from the > days when dialling brethren worked in chords, or lines drawn across a > circle, instead of using protractors and pocket calculators or computers > as we do today. The substyle distance is the angular deflection of the > gnomon from the vertical as would be seen in a full-face photograph. > Around it the hour lines cluster symmetrically. But what of the style > height? It is an angle sticking out of the wall at right angles to the > plane of the dial plate but inclined to the vertical by the amount of > the substyle distance. The combination of style height and substyle > distance defines the style and reflects the direction of the earth's > axis. Now it has been said that a dial may tell the correct time > anywhere in the world where the sun shines so long as the dial plate and > gnomon are in the same relation as in the place for which they were > made. Perhaps you remember the photograph that Mike Cowham once > displayed of the English dial on the wall of the parish church in > Stellenbosch in South Africa. People laughed at the ignorance of the > vicar who supposedly pinched the dial from his parish church on the > English south coast and set it up there. Of course, the sun goes round > anticlockwise in the southern hemisphere so the hour lines read > absurdly. But if the dial were to be turned approximately horizontally > to be in the plane of southern England it would tell the time well > enough. > > What then of the style height. We have said that the gnomon of a south > facing dial sticks out of the wall at an angle of ninety degrees minus > the latitude. With a non-south facing dial it is at different angle. > For instance, in my latitude, 55 deg. north the style height is 35 deg > with a south wall but with a wall declining 30 deg from south it is > about 17 deg. Note that the longitude where I live is close to 0 deg. > Let us now convey our 30 deg declining dial to latitude 73 deg north and > make the gnomon vertical (substyle distance = 0deg) Now the hour lines > are clustered symmetrically around the gnomon as in a south-facing dial > but they are telling the wrong time. The error is the substyle > distance, 31 deg, in hours and minutes. Can we correct this? Simple. > Just move the dial to 31 deg west and it's telling the right solar time, > corrected for longitude. My question, Chairman, is, are there > intermediate points between 55 deg north 0 deg and 73 deg north, 31 deg > west where the dial can also be made to tell the right time, and do > these points lie on a great circle. Please hasten with your replies as > I am not sleeping at all well because of it all. > > Frank > > -- > Frank Evans >
