Sonne & Zeit - Sonnenuhrenbau Heierli

A New Star in Sundial Heaven

What is unique about our sundials?

The hour lines of a sundial are determined by nature. Changing their shape means changing the physics involved.

On classical sundials showing true solar time, the hour lines are shaped as straight lines. The design appeared in Europe around 1450 and is still very popular today. Its advantage resides in the simplicity to construct the hour lines. But there is also a disadvantage: The hour lines look like irregularly spaced spokes of a wheel instead of revealing what they really are:  regular longitude lines of the Earth. 

Snell's natural law of refraction of 1621 has left the door slightly ajar to create a plane sundial whose hour lines confound with the longitude divisions, but no one realized that for almost four hundred years. The trick consists of letting the sunlight pass through a camera obscura filled with a refracting medium. This setup changes the direction of the incoming light and thus the shape of the hour lines. On the back side the ray forms a bright spot moving along the dial as the Sun moves through the sky. If all is adjusted well, the hour lines for this bright spot take the shape of the Earth. Our patent is currently pending.

The animation below shows transitional stages between the classic sundial and our design.

The classical dial

Transitional stages (animation)

Our dial, developed 2012


The animation below was recorded on October 13 in Schaffhausen, Switzerland, on a cloudless day between 12:40 CET and 13:50 CET. It shows the path of the bright spot in quick motion in steps of 2 minutes. The declination of the Sun was -7.9 degrees. Sundial : Model Meridiana for time in CET

(CET = Central European Time, Time in CET = Time in CEST minus 1 hour).

Note: If the animation is frozen, try using another browser such as Firefox.

Reading time

Our sundials display two measures of times : standard time and true local time. Please note that they are always configured for your time zone, anywhere on the world.

How to read apparent local time (solar time)

Local time is shown by the position of the middle of the bright spot with respect to the dotted "longitude" lines marked with roman numerals. On our example, the bright spot is between the XI o'clock line and the XII o'clock line, closer to the first: it is twenty past eleven local time.

How to read standard time (watch time)

The photo on the left occurs twice a year, on March 4 and on Oct. 11. So to read the standard time, you need to know the season. If you are in the half-year between Dec. 21 and June 21, the black hour lines apply. In the other half-year the red hour lines apply (see bottom line on sundial).

On March 4 it is exactly 12 o'clock (black hour line). On October 11 it is 11 : 40 (between red hour lines 11 and 12, closer to the latter).

Apparent local time (solar time)

The apparent local time or solar time indicates when the sun is exactly in the south. This happens on solar noon or 12 o'clock solar time. From one solar noon to the next, the time is divided into 24 hours. Since the sun does not always move through the sky at equal speed, the solar hours are not always same length. The duration of solar hours can deviate up to 1.25 seconds from the normal hour.

Formula : Apparent local time = hour angle of the sun - 12 hours, modulo 12.

Standard time (coordinated zone time)

The standard time is the time on your watch. Unlike solar time, it runs at an even pace, except for inserted leap seconds. It is corrected periodically in order not to run away from the sun. Without leap seconds, "lunch time" would slowly drift away from the middle of the day into the morning hours.

What happens when changing the clocks ?

The Sun does not care about us changing the clocks. In the summer months you need to add one hour, e.g. 4 o'clock winter time is 5 o'clock summer time..

How accurate are our sundials ?

If the sundial is aligned accurately, you can read the time with a precision of a few minutes. If left alone, sundials  never loose their accuracy. The watch on your wrist needs many more readjustments than sundials.

How do I properly align the sundial ?

Pay attention to a horizontal footing and as many sunshine hours as possible. The first time you set it up, rotate it until it shows the exact standard time, taking into account summer time if necessary. Once aligned the sundial will show the right time for the rest of the year and the following years as well.

If you temporarily need to move the sundial, e.g. to cleanse it, apply a ruler or another straight object to it, remove it and put it back in place according to the ruler. This way you do not need to re-adjust it. 

Cleaning and maintenance

To cleanse the sundial, use a moist cotton towel. Never hold it underwater or under the tap. We do not guarantee waterproofness.

Can I take the sundial in the garden ?

You should not. It is not designed to be waterproof or rainproof. Of course you can set it on a garden table during sunshine but take it in before rain comes. Our dials are designed for the interior window sill.

Why do we ask for prepayment when you place an order ?

Every sundial is a unique piece, specially built on your demand for your exact location and window orientation.

How do I find out the longitude and latitude of the house in which the sundial is set up ?

Of course, we do that for you. We just need the address. The information you give us is treated confidentially and is only used to configure your sundial.

How do I find out the orientation of my window sill ?

1. Either you find out from the construction plan of your building.

2. Or we determine it from publicly available geodata provided by your country. For this you must tell us on which facade you plan to put your sundial.

Again, the information you provide is treated confidentially and is only used to configure your sundial.

Sonne und Zeit

Sonnenuhrenbau  H e i e r l i

Wagenstrasse  1 6

8200  Schaffhausen

Schweiz  .  Suisse  .  Svizzera

      U I D : C H E - 4 5 7 . 1 0 7 . 6 6 6

      I n h a b e r :  D r . - I n g .  J .  A l b e r t   H e i e r l i

      w e r k s t a t t @ s o n n e u n d z e i t . c h

Literature (in German)

1. P. Hugo, D. Roth, W. Bachmann, Sonnenuhren Deutschland und Schweiz, DGC, Stuttgart, 1994.

2. Jörg Meyer, Die Sonnenuhr und ihre Theorie, Verlag Harri Deutsch, Frankfurt am Main, 2008.

3. Arnold Zenkert, Faszination Sonnenuhr, Verlag Harri Deutsch, Frankfurt am Main, 2002.

4. G.D. Roth (Hrsg.), Handbuch für Sternfreunde, Band 1, Springer Verlag, Berlin, Heidelberg, 1989.

DGC: Deutsche Gesellschaft für Chronometrie.