Landscaping & Gardening Information | home | site map | contact us |
The Sundial - Garden Ornament or Exotic Timepiece?
Most of us regard a sundial as an attractive ornament fora park or garden. Their effectiveness as time keepers ishighly 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, affordablewatches 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 theseasons and the movement of the sun to determine planting andthe 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 wasperfected. 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 beautyand interest to the home garden. Related is the equatorial sundial, with its dial oriented at the same angle as the latitude. It works slightlydifferently, and is easier to use when properly calibrated. Thirdly, there is the vertical sundial, ideally locatedon a wall facing due south in the northern hemisphere, andnorth in the southern hemisphere. The principle is much thesame, 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 about1/30th of an inch, or just under 1mm, in a minute. This maybe 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 otherway. The sun appears to move from east to west across thesky, 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 alunch 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 communicationsand transport became faster. Imagine calculating train timetables when Boston, New York and Buffalo all workedon 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. Boundarieswere altered slightly to account for state and nationalborders. 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 thesemeridians (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 thisarticle. 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 inyour 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. Andwhere 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
MORE RESOURCES: Unable to open RSS Feed $XMLfilename with error HTTP ERROR: 404, exiting |
RELATED ARTICLES
Choosing the Right Roses for Your Garden The selection of roses you can grow in your home garden is enormous. With so many to choose from, finding just the right ones may seem more like work than play. Kirengeshoma palmata Kirengeshoma palmata Sometimes known as yellow waxbells, Kirengeshoma palmata is a late-flowering rhizomatous perennial up to 1.2m high with arching stems and is native to the woods and mountain lowlands of Korea and the Japanese islands of Shikoku and Kyushu. Taming Your Outdoors Slapping yourself silly trying to keep mosquitoes from biting you? Besides causing irritating itching bites, mosquitoes can also carry and transmit several diseases including the West Nile Virus. Although you cannot get rid of every mosquito, there are many ways to protect yourself and those around you. Fish Health in Hot Summer Heat Summer is over, but for many of us - the heat remains.Here a couple of things to do to keep your fish healthyand your pond clear going into winter. Gardening Tips for Early - Mid July Now we are fast approaching the hottest time of the year, there are still some things that can be done in the garden. Below are a few gardening tips for those that love the summer warmth. Teak Furniture - A Cut Above The Rest As you shop around for outdoor furniture, you will notice that much of the higher quality pieces are made from teak wood, and for good reason. Teak furniture is not just sturdy and durable, but also very beautiful with rich warm tones. Dont Roll that Lawn Every spring some mysterious hormone hits the male of the species and the urge to "do lawn work" strikes.One rite of spring is act of rolling the lawn. What Type of Gazebo is Right for You? Top Questions You Need to Ask Having a gazebo in the backyard is an excellent way to enhancethe appearance while providing you with a quiet place to sit andrelax after a hard day at work. Gazebos are wonderful forbarbecue parties, family gatherings, or simply sipping on a cupof coffee or glass of lemonade on a lazy day. A Garden Bench: A Beautiful Addition To Any Garden Okay, so you have spent hours upon hours creating the perfect garden. You have chosen only the choicest flowers, agonized for days over their placement, and even bought that much too expensive antique statue to set it all off. Hydroponics Gardening - An Introduction To Hydroponics Gardening For Beginners (part 4) Environment THE BASICS OF HYDROPONICS.The Success or Failure of Your Plants Depends On Their EnvironmentThe environment, or climate, in which your plants are grown is one of the most important factors affecting your end results. The Indoor Garden: Plants that Clean the Air There are many reasons for creating an indoor garden - significant among them is the need to clean the toxins from our homes and offices. As a consequence of the energy crisis in the 1970's, today's homes and offices are built to conserve energy and the outcome has been a lack of air exchange, with the resulting increase of indoor air pollution. What Is One Flower Benefit That You Know Of? The biggest flower benefit of all is the fact that flowers make you happy.Research has proven this. How To Grow Luscious Tomatoes The tomato is the most commonly grown vegetable in theStates. Here are some tips on how to grow your ownbountiful crop of tomatoes. Why Teak Coffee Tables Are Essential For Your Outdoor Space One of the best ways to bring together the many pieces of furniture in your outdoor space is to accessorize with teak furnishings such as teak coffee tables. By placing a teak coffee table in your space, you create a feeling of completeness and hominess that is just not captured by most who try to decorate their outdoor spaces. No Dig Gardens - How to Build One The no dig garden is exactly what it describes.. How to Water Your Houseplants Wisely Over watering ranks first in causes of houseplant demise because it causes roots to rot. Most plants are tough so they can recover from under watering with only the loss of a few leaves -- unless you wait too long and pass the point of no return. New for 2006 - Granite Flexible Preformed Rock Ponds Traditionally, preformed ponds are large shells, which are extremely burdensome and difficult to transport. For example, a typical preformed pond kit would come in a box that is 60" x 48" x 24", which is too large for many car trunk sizes. Earthworm Friends in the Garden Earthworms are a gardener's best friend.Research has shown that earthworm excrement, also calledcastings or vermicompost, improves the aeration, porosity,structure, drainage, and moisture-holding capacity of soil. The Swallowtail -- A Beautiful Butterfly Swallowtail butterflies are some of the most beautiful butterflies found anywhere. The North American species are large, brightly colored butterflies with tailed, rear wings. With Outdoor Lighting You Can Enjoy Your Garden Into The Evening Hours It is a beautiful evening and you are relaxing on your patio, enjoying the cool summer air. The flowers are blooming, the lawn is green and lush, everything is perfect, if only you could see! We spend so much time and money on our backyards, decks and patios, and then the sun goes down and we must abandon these beautiful oases. |
home | site map | contact us |