FREQUENTLY ASKED QUESTIONS (in  preparation today!)

1.   How accurately does a sundial tell the time?

When a sundial has been accurately designed and made for the latitude, longitude and time zone where it will be used, it should tell correct time to about one or two minutes for centuries to come.

2.   Someone bought me a sundial from a shop. It doesn't tell correct time! Can it be fixed?

Generally, sundials bought from a shop do not tell correct time because they have not been designed for your location. They are just ornaments and can not be fixed to tell correct time. 

3.   Where should I put my sundial?

Find a nice sunny spot in your garden where no shadows will be cast from nearby trees or houses. If you can, experiment a little with different times during the day and year to see where these unwanted shadows fall.

4.   How much does a sundial cost?

A cast bronze horizontal sundial with a plain gnomon designed personally for you and accurate for your location will cost about $500 for a size around 310 mm (circular, octagonal, square or designed to fit an irregular base such as a rock). A larger size around 400mm will cost $650. See Prices and Delivery for more details about other types such as armillary sphere sundials. Relatively unusual types of sundials are costed individually.

5.   How long does it take to produce my personalised sundial?

For a complex sundial, the design may go back and forth several times via email or personal consultations before it is finalised. Once finalised, for a cast bronze sundial we quote 4-6 weeks for delivery to your location within Australia. We use Australia Post parcel service or courier delivery depending on circumstances. More unusual sundial commissions make take several months to complete. We update you frequently on the progress of your commission.

6.   Is there a special name for people who make sundials?

The art and science of making sundials is known as 'gnomonics'. This word is derived from the Greek word 'gnomon', meaning pointer or indicator. A gnomon is the part of the sundial which casts its time-telling shadow onto a scale marked out in hours and minutes. People skilled in gnomonics are known as 'gnomonists'.

7.   How do I set up my sundial?

You need to set most types of sundial so that the gnomon points towards the South Celestial Pole. This means that the gnomon should be inclined to the horizontal by the angle corresponding to your latitude and facing True South (not magnetic South). The sundial shadow will then indicate solar time. (Rare types such as Pillar sundials operate quite differently.) With any accurately designed sundial, it is easiest to set the sundial up so the shadow indicates correct solar time once you have allowed for the various differences between solar and local time. Your Sundials Australia sundial generally displays these values in graphical form on the sundial face. We supply detailed installation instructions with every sundial.

8.   Do sundials work during Daylight Saving Time?

Daylight Saving is used in many states and countries to optimise the hours of daylight and to reduce power consumption for lighting and climate control. It is an artificial time, a man-made convenience convention, where one hour is added to the local Standard Time. Rotating the gnomon to compensate is a wrong thing to do because the gnomon needs to face True South.  It is sometimes (rarely) possible to rotate the hour scale of an Equatorial sundial on the date of the equinoxes to compensate for daylight saving, but not for any other type of sundial. The simplest technique with all sundials to simply add one extra hour to the time indicated by the sundial shadow.

9.   Can I still use my sundial if I move to another location?

It's worth taking your personalised sundial with you when you move, but you will need to make some adjustments to what the shadow now reads or your sundial will be incorrect at the new location. The change in latitude is allowed for by tilting the body of your sundial so that the top of the gnomon still points to the South Celestial Pole.  The sun travels 360 degrees around the Earth in 24 hours so every degree of longitude change from your old to your new location requires that you add or subtract an extra 4 minutes to what the sundial shadow reads at the new location. 

10.   How long have sundials been used?

Sundials in various forms have been used for more than 5000 years. 

The Greek historian Herodotus (484−425 BC) stated in his writings that sundials originated with the ancient

Chaldeans and Sumerians who lived in Babylonia between the Tigris and Euphrates rivers, in the region formerly called Mesopotamia and now known as Iraq. They used vertical rods on their buildings as shadow casting devices for telling the time and the date, and were the first people to divide the day into 24 hours, the week into 7 days, and the year into 12 months (after first having divided the sky into the 12 signs of the zodiac.)

 

The Greeks created a great variety of sundial types. They had many public sundials consisting of tall columns casting shadows onto the ground, and many citizens had their own sundials. Aristophanes’ play ‘The Frogs’ written in 405 BC contains the line “When the shadow is ten steps long, come to dinner”.

In those days, a system of ‘unequal’ or ‘temporary’ hours was in common use, with the available period of daylight divided into 12 parts − resulting in 12 long daylight hours in summertime and 12 short daylight hours in wintertime. Astronomers, however, used ‘equal’ hours (just as we do today) for charting the moving heavens.

 

The Romans are not believed to have developed any new sundial types, but they certainly used all the Greek sundial developments, and sundials were extremely popular throughout their empire. Surviving specimens of Roman portable sundials have been found designed for latitudes from Britain through Narbonne in France to Ethiopia and Mauritius.

 

From these beginnings, methods for designing and constructing various types of sundials have been developed by many different cultures right through to the present day.

 

In addition to telling the time using lines and numbers marked on a dial plate, sundials needed to have human appeal. Fine craftsmen developed high levels of artistic skill and decorated their sundials with embellishments of every kind. This artistic decoration, or ‘furniture’ as it is called, required many hours of labour to be carried out on both the dialplate and the gnomon (the part which casts the shadow). Many of these old sundials are now valuable family heirlooms and very costly antiques which only museums and the like can afford to buy. As a direct consequence of the design difficulties and the labour required

to produce a sundial, most people were unable to afford the high cost of such instruments.

Consequently, the owners of these enduring sundials throughout history have been the richer people in society, and public institutions such as cathedrals, parks and town halls.

 

The sundial is the oldest known scientific instrument.  It is even mentioned twice in the Bible. (II Kings and Isaiah)

10.  Can you recommend any good books about sundials?

There are several good, classical texts about sundials but all are written for sundials in the Northern Hemisphere, where the gnomon points towards the Pole Star. In the Southern hemisphere, the gnomon needs to point to the South Celestial Pole (we have no equivalent star to make things easy) so morning and afternoon hours are reversed in the two hemispheres. Our book, 'Sundials Australia' is the first book written from a Southern Hemisphere perspective.

‘Sundials, How to Know, Use and Make Them’

Mayall, R.Newton and Mayall, Margaret W.

Sky Publishing Co., Cambridge USA,

Second Edition 1973 (First Edition 1938)

Library of Congress Number 73–76242

 

‘Sundials, Their Theory and Construction’

Waugh, Albert E

Dover, New York USA, 1973

 

‘Die Sonnenuhr’

Rohr, Rene R.J. (in German)

Callwey Verlag, Munchen Germany, 1982

 

‘The Exhaustive Treatise on Shadows’

al-Biruni, Ahmad original text 1050 AD.

Facsimile and Translation by the University

of Aleppo, Syria, 1976