|
Author: Graham McClung Article source: http://www.gatewaytosedona.com/. Used with author's permission.
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 that the 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 of the few ways to tell
the time with reasonable accuracy.
Shadow clocks dated at 1500BC are known from Egypt, but
the first dials appear to have been Babylonian. The
Greeks adapted the idea, the Romans developed it further,
and by about 100BC had perfected the 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 of the
seasons and the movement of the sun to determine planting and
the 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 of the
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, called the gnomon (silent "g")
which casts a shadow onto a plate called the dial.
The dial is divided into hourly or shorter time divisions
and may also show other information.The part of the gnomon
whose shadow indicates the time on the dial is called
the style.
The most abundant form is the horizontal sundial,
happily sitting on its pedestal or column and adding beauty
and interest to the home garden.
Related is the equatorial sundial, with its dial
oriented at the same angle as the latitude. It works slightly
differently, and is easier to use when properly calibrated.
Thirdly, there is the vertical sundial, ideally located
on a wall facing due south in the northern hemisphere, and
north in the southern hemisphere. The principle is much the
same, but the sundial only occupies a semicircular area.
Vertical sundials displayed the time to the public, and were
used to correct unreliable public clocks.
And the most elegant of all, the 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, and the compass
defines north. Pretty neat!
Sundial Accuracy
A properly designed and installed sundial can be a very
accurate means of telling the time, down to intervals of
less than a minute.
I won't go into the mathematics, but on a sundial 16 inches
(40cm) in diameter, the shadow of the gnomon will move about
1/30th of an inch, or just under 1mm, in a minute. This may
be small, it's enough for our eyes to see.
Two Major Problems
Apart from the frequent absence of sunlight (Problem 1),
all sundials show time by calibrating outwards from the
position of the sun at noon. If you live east or west
of me, your noon is different to mine.
Although the earth moves around the sun, we see it the other
way. The sun appears to move from east to west across the
sky, and local noon is when it's vertically overhead.
But if you live 100 miles west of me, my noon is still your
late morning, and your noon is my early afternoon. This
would be inconvenient if we used our sundials to arrange a
lunch date, but a real problem if I had a plane to catch in
another city.
Solar Time and Official Time
People managed to live with this problem until communications
and transport became faster. Imagine calculating train
timetables when Boston, New York and Buffalo all worked
on different local times.
The answer was the development of local time zones.
US Railways did this in 1883, but in 1914 the world's
governments agreed to divide the globe into 24 zones,
each 15 degrees of longitude in width, and each one
hour different in time to its neighbours. Boundaries
were altered slightly to account for state and national
borders.
There are four time zones in the contiguous 48 states of the
USA: Eastern, centred on 75 degrees W longitude; Central, on
90 degrees; Mountain, on 105 degrees; and Pacific, on 120
degrees. Noon was identified astronomically for each of these
meridians (now it's done by atomic clocks), and accepted
everywhere else in the zone.
Noon on sundials in places very close to these longitudes
will correspond to official noon. For every degree east
or west of the central meridian, for 7.5 degrees either
side, you will need to add or subtract four minutes
respectively to correct your sundial.
A few other adjustments are necessary to compensate
for irregularities in the earth's path around the sun -
not too difficult to make but the theory is beyond this
article.
They add to the inconvenience, and that's why sundials have
been superceded by more convenient and reliable forms of
time keeping. But problems with time zones and orbital paths
can be corrected, and there's no reason why you can't find
the correct time from your sundial.
No reason, that is, provided it has been properly installed in
your garden. And that's the subject of another article. Copyright 2005, Graham McClung.
A retired geologist, Graham
McClung has had a lifelong interest in the outdoors. And
where there's outdoors there's weather. He is the editor of
http://Home-Weather-Stations-Guide.com, where you can find reviews
and advice to help you choose and use your own home weather
station. You can contact him by email at
information@home-weather-stations-guide.com
The 7 Traits of an Exceptional & Successful Entrepreneur
Are you open to explore what's preventing you from achieving the level of succcess you want ?
The Power of Dogs
I owe it all to Stitch without him, none of this would have ever materialized, he played so many vital roles in this business and ultimately changed my life, wi...
Top 4 Reasons Women Ride The “Emotional Roller-Coaster”
Women have learned and are in the habit of being driven by the approval of others. Most women allow the expectations of others to define them and therefore maki...
It’s Not All About Cheese: The Missing Component in Employee Development (Part 2)
In this two-part article, author Julio Quintana talks about the missing component in Employee Development. He also shares excerpts from his new book, Merge Poi...
How To Explode Your Web Sites Traffic With Articles Permanently!
There is one golden rule, which is inherent in this free and extremely effective internet marketing strategy. First GIVE, and then TAKE. It's as simple as that....
Bird Watching – Writing What You See
No bird watcher is complete without his or her bird watching journals. When you go bird watching, you need to keep your life list.
Online Dating. Is It Taken To Seriously?
When I look at alot of the online dating services I notice one common trend. People take it very seriously into finding there true love. I find it absolutely am...
ATM (Ataxia Telangiectasia Mutated) Antibodies from Imgenex
ATM, the gene product mutated in the cancer susceptibility syndrome ataxia-telangiectasia, is related to proteins involved in DNA repair and cell-cycle control....
Where to buy a Used Digital Camera
Christmas coming up and the fact that soon many people will be trying to get rid of their unwanted gifts, it will shortly be boom time in the used digital camer...
Autoresponders Make You Look Like A Pro
Using autoresponders not only save you time, but also give you a more professional look and feel to your business.
A Look At Roulette Gambling
For the novice gambler, roulette gambling seems like a very difficult task to learn. It is true that learning the strategies used by pros can take years of expe...
Beating the Weight Loss Bandits
If you're on a weight loss program you're under constant attack - attack from the food bandits all around you. There is food waiting to ambush your weight loss ...
Mortgage Basics for First Time Home Buyers
Anyone planning to take out a mortgage for the first time will most likely find the job a little daunting, not least because the financial jargon can often be v...
Avandia Side Effect Lawyer: Diabetes Drug Damages Liver
Avandia is an oral antidiabetic agent that increases insuline sensitivity for patients with type 2 diabetes, or non-insulin-dependent diabetes. Avandia is in th...
Why Commercial Real Estate is the Hottest Retirement Asset
For Successful Small Business Owners, Commercial Real Estate Investment is the Hottest New Retirement Asset
10 Most Important Things to be Careful About While Outsourcing
It is often asked what one needs to be careful about when choosing an outsourcing company or individual...
Build Wealth From Home
Build Wealth From Home As you sit in traffic, inching along between irate drivers, you think to yourself, "there must be a better way." You get to work, you e...
Top 20 Dog Quotations
Get to know your beloved dog better with these insightful quotations all about your best four-legged friend...
Fuel Prices at the Pump: That is not the problem, Natural Gas Prices are high too
Natural Gas, oil, energy and flow of fuel; inter related issues.
Water: The Best Medication Ever Created!
The initial finds are conclusive. Sick people do not drink enough water every day. This is something worth thinking about and applying to your own health regi...
What is the Meaning of Life?
There is much to learn from our children and all of us must be able to learn as if we are children...
Nutrition for a Healthy Lifestyle
Here we will discuss nutrition for a healthy lifesytle with some of the benefits to a sound nutrition plan.
Why Should You Meditate?
Your mind needs rest and a vacation. Have you ever noticed that when you take a vacation, you come back with fresh ideas, a better attitude, and establish clea...
Aluminium And Wooden Greenhouses
A look at the individual merits of aluminium and wooden greenhouses.
|
Print this page