The Sundial - Garden Ornament or Exotic Timepiece?

Written by Graham McClung

Most of us regard a sundial as an attractive ornament for a park or garden. Their effectiveness as time keepers is highly variable

That's unfortunate, because it is not at all difficult to ensure that your garden sundial will be an accurate timepiece, provided, of course thatrepparttar sun is shining.

But that will be covered in another article. For now, let's see what a sundial is, and what it is capable of.

Sundial History

We forget in this modern age that accurate, affordable watches and clocks have been around for much less than 200 years.

Before then, sundials were one ofrepparttar 113290 few ways to tell repparttar 113291 time with reasonable accuracy.

Shadow clocks dated at 1500BC are known from Egypt, but repparttar 113292 first dials appear to have been Babylonian. The Greeks adaptedrepparttar 113293 idea,repparttar 113294 Romans developed it further, and by about 100BC had perfectedrepparttar 113295 horizontal sundial (and placed it in their gardens).

Even in ancient days some people had schedules to keep, and both agriculture and religion required knowledge ofrepparttar 113296 seasons andrepparttar 113297 movement ofrepparttar 113298 sun to determine planting andrepparttar 113299 timing of ceremonies.

The sundial was an important means of providing that information, and considerable advances in mathematics, geometry and astronomy were made while it was perfected. The knowledge gained forms part ofrepparttar 113300 foundations of modern science.

Types of Sundial

There are four reasonably common types of sundial.

They all have two things in common. Each consists of a raised structure, calledrepparttar 113301 gnomon (silent "g") which casts a shadow onto a plate calledrepparttar 113302 dial. The dial is divided into hourly or shorter time divisions and may also show other information.The part ofrepparttar 113303 gnomon whose shadow indicatesrepparttar 113304 time onrepparttar 113305 dial is called repparttar 113306 style.

The most abundant form isrepparttar 113307 horizontal sundial, happily sitting on its pedestal or column and adding beauty and interest torepparttar 113308 home garden.

Related isrepparttar 113309 equatorial sundial, with its dial oriented atrepparttar 113310 same angle asrepparttar 113311 latitude. It works slightly differently, and is easier to use when properly calibrated.

Thirdly, there isrepparttar 113312 vertical sundial, ideally located on a wall facing due south inrepparttar 113313 northern hemisphere, and north inrepparttar 113314 southern hemisphere. The principle is muchrepparttar 113315 same, butrepparttar 113316 sundial only occupies a semicircular area. Vertical sundials displayedrepparttar 113317 time torepparttar 113318 public, and were used to correct unreliable public clocks.

Andrepparttar 113319 most elegant of all,repparttar 113320 portable sundial. George Washington had one - at that time pocket watches were most unreliable. Modern examples can be a work of art. They combine a compass with an adjustable dial. The dial is tilted to correspond to local latitude, andrepparttar 113321 compass defines north. Pretty neat!

The Perfect Garden Sundial

Written by Graham McClung

Is it possible for a garden sundial to tell perfect time?

The chances are very good if you can make one yourself, or get one custom made for your location. But both these alternatives will take either time or money.

The reason for this is that apart from adjustments for time zones and daylight saving , covered in another article, there are three things that must be done.

Compensating forrepparttar Earth's Path Aroundrepparttar 113289 Sun

Ifrepparttar 113290 earth followed a perfect circle as it revolved aroundrepparttar 113291 sun, life with sundials would be easy. But its path is elliptical or oval, and this causes errors of up to 16 minutes in sundial time at some times ofrepparttar 113292 year. The corrections are straightforward, and can be made using a table, or from a figure 8 line calledrepparttar 113293 Analemma, often seen on old globes and sundials.

Correcting for Latitude

Let's considerrepparttar 113294 components of a sundial for a moment. It consists of a dial on whichrepparttar 113295 time divisions, and sometimes other information is marked, and a triangular piece which sits vertically onrepparttar 113296 dial. It is calledrepparttar 113297 gnomon, pronounced nomon, andrepparttar 113298 part which castsrepparttar 113299 shadow ontorepparttar 113300 dial is calledrepparttar 113301 style.

For more information on how sundials work, including how to design your own, go to Google and type "how + sundial", withoutrepparttar 113302 quotes but withrepparttar 113303 +, inrepparttar 113304 search box.

To be accurate,repparttar 113305 angle betweenrepparttar 113306 triangular part ofrepparttar 113307 gnomon andrepparttar 113308 horizontal must berepparttar 113309 same asrepparttar 113310 latitude ofrepparttar 113311 place it is to be placed in (You can findrepparttar 113312 latitude - and longitude - of your home from any topographic map or good atlas).The arrangement and distance betweenrepparttar 113313 hour markings onrepparttar 113314 dial must also be correct forrepparttar 113315 latitude.

Hmmmm! This means that unless you are very lucky, that elegant sundial in your local garden supply shop will probably not showrepparttar 113316 time particularly well. It may be calibrated for an average latitude (commonly 45 degrees), which is good if your latitude is not too different. Or it may be purely ornamental and will really only be useful around noon.

Now of course this doesn't matter at all if you are looking for something pleasing torepparttar 113317 eye, and don't mind answering repparttar 113318 inevitable question "Does it tellrepparttar 113319 time?" But if you'd like your sundial to be more useful, make sure you find out which latitude it is calibrated to.

Once you know this, all you need to do to compensate is to work outrepparttar 113320 difference, and tiltrepparttar 113321 dial towards or away from due south depending on whether you need to add to or subtract fromrepparttar 113322 latituderepparttar 113323 sundial was designed for. There may be slight differences torepparttar 113324 ideal spacing ofrepparttar 113325 hour marks, butrepparttar 113326 apparent time will be reasonably close.

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