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On the southern countries where one go to the sleep on the roof of the house and gets show daily the wonderful star sky does not surprise it that especially these people (Babylonians, Persians, Arabs ...) have made themselves around the progress of the astronomy deserving.

Also the today's names of the signs of the zodiac go back to them. Indeed, these signs of the zodiac of the astrologers have moved on the basis of the sun for about 2000 years around a sign of the zodiac, so that, e.g., the sign of the zodiac Aries lies today before the sign of the zodiac Fish.

For sundials these signs of the zodiac do no sense. They can be used only as a pure decoration.
Indeed the discrepancy between our by machine identical-divided clock time and the a little bit irregular way of the earth around the sun does not strike in a human life, however, after several generations one will see this also with the date lines, because the position of the ecliptic (declination) changes in 40 000 years around ~2.5 ° (This does not affect on the exactness of the hourly announcement!). Today with a 300 year-old vertical south clock with a meter long shadow pointer the shadow length differs in June 2 cms, in December 0.5 cms.. The big time equation loop belongs in Bologna of San Petronio, e.g., also to it , [2] Arnold Zenkert p.144.

Detail of eight loop for 13°° o' clock. The calculation of the pointer point is necessary for the construction of the date lines, a personal date babylonian or italian hours or to fix a hole screen on the pointer.

The widespread confusion of definations in the Gnomonic one has tried to obviate in [6] Arbeitskreis Sonnenuhren p.4.8 with extensive definations explanations. Then, e.g., old hours (antique, biblical, Jewish) have no straight lines (recognizably, however, only with phi> 30 ° K. Schoy in 1925 p. F.29), and are longer in summer and shorter in winter, because one divides the bright day in that case into twelve identical parts, while italian or bohemian and babylonic or Greek hours straigt lines are and her hourly length with the AST/MST is comparable.. The Babylonic are calculated by sunrise.

Italian hours are calculated by the preceding sundown and are indicated with a point pointer. If one complements the hours to 24, one receives the hourly rest to sundown.
Before the invention of the light bulb the length of the bright day was especially interesting around the Mediterranean. For today's any day people, extreme stream savers and sundial enthusiasts can be of this one interesting announcement. In Ticino (Switzerland) one finds even today some sundials with this dial.

In Europe the period of time of prosperity of the sundial makers was this from the 16th to the 18th century in which the "compass makers" performed good craft and design.

You can see also, that several dials are explained like AST, CET, noon of some cosmopolitan cities ....

True noon representated with Roman XII In any case it is advisable with the CET-figure sheets the true noon (XII o'clock solar highest position) to marked, because, nevertheless, with 12:00 clock noons one associate with the solar highest level unconsciously. With the standard time CET - therefore also with the time announcement on radio: " Now it is 12:00 o'clock " (noon) - is shifted as a rule around something.

Without Theory it does not go

After I have read something in literature to mind as an amateur, got used to myself something with the professional vocabulary and have tried to understand the descriptions of the authors to the sundial construction, I had to find out that it was not always quite easy especially with the mathematicians and is if the spheric trigonometry and " shifting of the sun " and similar are mentioned. With the calculation and arrangement of the pointer it was similar.

Stonecutters and sculptors work more with drawings, practical "take a bearing of things" and with aids.

The authors often use different names for the same object.

With the real calculations this is especially confused if the signs are forgotten, the angle sometimes by north, then from south is measured. One must take care for whether the author works just with the horizon, equator system or already with the spheric trigonometry.

If one is surprised at the arithmetic result, one is glad if one finds out with another author by the way that it is usual in the astronomy a time measure to insert just like that as a degree into formula. To be say nothing from misprints and write errors.

Has one calculated, finally, for a plausible result, does one ask himself, do I mark the value now on the right or on the left from the perpendicular ....?

The problems with the literature not least also the trouble lies at my own limitedness! The authors have mostly done big trouble to themselves and in the recent literature there are also three-dimensional representations like it runs thus between sky and earth.

Luckily there are various sundial programs which make easier a lot, however, not the knowledge what is hidden behind the values to be given.

Now, I am already as a child gladly go mushrooming, because it an interesting thing is till one the next finds. And something else is not the hobby here probably also!?

My Pointer Shoe, a practical Result

My " go mushrooming " has been worthwhile! At least, nevertheless, at the end the useful result of the "pointer shoe" is created!

In his variation as a pointer"sail", it is an easy and comfortable solution especially the connection with two screws-for a wall which does not show exactly to the south or another direction (= divergent wall or declinated wall).
These sundials on divergent walls are the most often seeming kind of wall-sundials. Indeed, the calculation and equipment of the pointer is connected for this case with some trouble and often expects too much of the do-it-yourself enthusiast.

The pointer shoe can be well used in paper/ cardboard to the control of the pointer stick. I cannot recommend the direct execution in massive material as a pointer, because it can come, on this occasion, to problems with the shadow measurement. Therefore, I have decided on his modified form as a pointer sail from metal or the like as a shade-cast pointer edge.

Who wants to connect the shoe with a stick (or style), should take care for the fact that the point of shoe of pointer get out of place.

An enlargement or reduction of pointer shoe with correspondingly factor is possible just like that if one does not change the angles.

Step by step

When can one mark the Hours?

In the end I have decided on the so-called "mark method", because this is more flexible than the calculations of the hours with her steady numerical values.

On four days with ± 0 of the ET (April 15th, June 13th, Sept 01st, Dec 25th) indicates the sundial exactly the Central European Time (CET) and you can mark directly the hours of the wristwatch on your sundial. Also the grandpa can adjust his old pocket watch directly after the sundial.

For the remaining days in the year the correction values are to be taken into consideration by the mark according of equation of time.

What signifies, e.g., "minus" / "earlier" in the equation of time?

The earth rotates at this time fastest on the sun (2nd law of Kepler), the sundial is fast therefore and the minute value is to be subtracted from the station clock.

One can add this correction values as an information and as a design element very well as a equalization-diagram of time ("negative" time equation with my sundials as a " correction during minutes ") to a sundial.

With "running" sundial two minutes are to be subtracted, e.g., on Jun 03rd from the read time of the sundial, with it them with the station clock (more comfortably is probably father's digital clock!?) agrees.

An afternoon sundial Including the ET every hour as an eight loop is already a little more luxurious

Manufacturing, Mounting and Check

Also slight inaccuracies are not only embarrassing, but, unfortunately, no more can be corrected if one has applied the clock already on a massive house wall.
With a separate plate which one in front of the house wall attaches this is still possible by a low diagonal position. Also the pointer sail can be bent carefully in his whole surface.

Thus one should assemble the pointer shoe in paper and his function test before one " everything in bronze cast " .

Design :

Of the sundial design it applies if one said of the wall sundials from earlier time that no clock is identical with a second one. One has here wide possibilities of design.

With the numerals of dial something has become a tradition that one takes the Roman numerals for the AST and the Arabian numerals for the CET.

It has also been earlier a good custom that one has straightened the number of dial to the sundial center and after the shadow of sun, thus a little diagonal. Unfortunately, this representation make a little more work for the maker and compelling in no way. With the Roman numerals is remarkable that have written the old sundial makers, e.g., IV as IIII (also on old pocket watches). I believe, it had designing intention.

A little Literature

[1] Heinz Schilt: Ebene Sonnenuhren, CH-Biel (im Selbstverlag), 1987

[2] Arnold Zenkert: Faszination Sonnenuhr, Frankfurt a.M. 2005

[3] Franz Embacher: Sonnenuhren bauen leicht gemacht, Köln 1984

[4] Heinz Schumacher: Sonnenuhren Teil1 und 3, München 1984

[5] Rene Rohr: Die Sonnenuhr, München 1982

[6] Sonnenuhren-Handbuch: Deutsche Gesellschaft für Chronometrie
Arbeitskreis Sonnenuhren, 1993

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