(The translation to English is maded by pc-program and by adding few corrects with my "know-how" :-) )
Notes on the " Subject Sundial "
Wenn man an mir nicht rückt,
auf mich die Sonne freundlich blickt,
dann zeig' ich jedem, der mich liest,
wie Zeit und Stunde friedlich fließt.


All "times" in the following explanations can be indicated without big problems on a sundial. Because the modern person quite simply compares his wristwatch to the sundial in most cases, the sundial for this case must the respective standard zone (e.g., in Central Europe CET: 15 ° E long., in California indicate the Pacific Time: 120 ° W long.) and receive a reference to the time equation. In the anglo-saxon countries the time of zone is also called Standard Time.
  • CET: Central European Time (or: S.T. Standard Time)= AST-ET-L+1h or =MST-L+1h
    Up to establishment of the railroad which needed a standardization with the quicker cruising speed the AST had made good services. From 1893 the CET became in Germany lawfully. It is a time of zone (practically the station clock of Warsaw to Madrid), goes out from steady day division, hourly division and minute division and relation meridian to 15 ° E long. (Görlitz) of Greenwich.

    Right: Back of my travelsundial

    In Madrid these both times show, e.g., a not low difference on account of the substantial difference of the degree of longitudes. The ET is with about plus below 5 minutes in summer of less of importance.

    Right: Front of my travelsundial

    Some countries also belong to the CET-time zone in Africa: Algeria, Lybia, Nigeria, Angola, ...

    The UT (Universally Time) counts to the today's air traffic. It is the middle time in the relation meridian 0 ° (Greenwich).

  • ET: Equation of Time
    One must make a distinction between ET (e.g., in January with "negative" sign). The astronomers and sundial makers count on this in her formulae since about in 1977 [H. Vilkner in 1977], and the "negative" ET [3], F. Embacher p.76, as an old definition it was used before it and today is appropriated to sundials (e.g., in January with "postive" sign) to determine the land-usual time of day (CET) in the sundial.

    In the early time of the mechanical clocks it was a self-evident fact to adjust the inaccuracy of these clocks after the sun. With it the sun went properly and the mechanical clock wrong and it became valid:

    ET= MST (wheels clock) - AST (Solar Time).

    Only with more precise mechanical clocks (e.g., naval chronometer in 1790) could be more exactly also calculated the ET and from 1834 the mechanical clock went properly and the sun wrong! Only in 1977 it came for the rearrangement to the new definition

    ET= AST (Solar Time)- MST (wheels clock)

    It is to be paid attention in tables also in recent publications to the signs!

    Thus one finds in a standard work [5] R. Rohr in 1982, p.207, 42 under the heading equation of time the values from old definition ("negative" ET).

    The ET- diagramm too seeing on my travel sundial would have to call, actually, "negative" ET, because it has the reverse signs of the real time ET right-wise.

    ... if the summertime (Daylight saving time) is not indicated sometimes on the sundial, it is a simple thing for everyone that he adds this one full hour (speak: plus one)!

  • AST: Apparent Solar Time (or: L.A.T. Local Apparent Time)= MST+ET or =CET+ET+L-1h
    Time containing for the respective location after the sun. Because the earth moves irregularly around the sun, day division, hourly division and minute division are also different from day to day. However, it has the advantage that with her at XII o'clock the solar highest level is indicated and is with it more connected with nature than the CET. In Görlitz is:

    12:00 o'clock CET= XII o'clock AST

    , if during four days in the year the equation of time is zero:

    April 15th, June 13th, Sept. 01st, Dec. 25th

    time equation
    Time equation for correction of sundial

  • MST: Middle Solar Time (or: L.M.T. Local Mean Time)= AST-ET or =CET+L-1h
    It would think, that steady day division, hourly division and minute division and refers to the individual location. It is no time of zone.
  • The Historical

    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.
    a personal date 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.

    Kriechisch und Welsch Stund

    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 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.

    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.
    pointer shoe in paper 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.
    eight loop 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.

    Roman signs

    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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