The A to Z Challenge is on! Hello and welcome to my Main blog. My name is Rose Anderson and I’m a romance novelist. Join me and more than 2279 bloggers and authors as we blog the alphabet throughout the month of April. My daily posts will be mostly history with some science topics here and there. I’ve chosen subjects that tickle my fancy, I hope you will find them interesting too.
Keep the topic rolling! If you have comments or questions, add them at the end of the post. I may not know the answer off the top of my head but I love research and would enjoy discussing my topics further. Comments can be made just below my bio in the tag section.
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Today’s Calliope’s Writing Tablet post is brought to you by the letter S ~
S for Sundials & Shadow Clocks
My very first exposure to the sundial came from an old movie I first saw in the late 1960’s. A neighborhood theater was playing Gone With the Wind, and my mother took me to see it. We sat through it twice. (You could do that back then.) That’s where I saw the sundial. It was sporting a quote from Benjamin Franklin: Do not squander time, for that’s the stuff life is made of. Cool quote and cool gadget. It’s funny what our minds hang on to. 🙂
⇐ Most people are familiar with the garden sundials that have face plates — a flat disk marked with numbers and/or incremental lines to indicate time. Some contain multiple markings that can also calculate other information such as the month and date. This plate is a name only, for this part of the device can be just about any shape — spherical, bowl-shaped, circular, half-circle, conical, or flat. No matter the shape, they basically all work the same — sundials specify time by casting shadows or shafts of light on the face plate.
Ancient timekeeping? What’s the point?
Sundials are the oldest known scientific devices used to measure time. The earliest found are the shadow clocks from ancient Egypt and Babylonia that date somewhere around 1500 BCE. But they weren’t the only ones measuring the passing of time. Studying time, be it in minutes, hours, days, months, season, or years was a keen passion of several ancient civilizations. The ancient Sumerians, Mayans, Greeks and Chinese, all devised clocks and calendars. Their processes for it were astoundingly accurate too. So much so, we’ve built our modern timekeeping on what they discovered through observation centuries ago. You might wonder about the need for timekeeping in the ancient world. It’s all about knowing. When you know, you’re not blindsided by annual floods or unsure when to plant your crops. Important things like that.
Man saw the passage of time in the heavens. Certain patterns of stars only came in view with the changing seasons, likewise the position of the sun on the horizon varied from point to point along the year. What’s more, the moon’s phases were regular and predictable. Then somewhere back on the human timeline of time-measurement another discovery was made. Someone noticed shadows grew longer and shorter depending on where the sun was in the sky. With that observation in mind, the first stick was planted in the ground and the shadows it cast measured and marked. And wouldn’t you know, the shadows fell nearly the same the next day and every few days made slight deviations until the sun took the next spot on the horizon and the seasons changed.
⇐The Greeks took the concept further than just a stick in the ground. They invented the pelekinon. All sundials calculate most accurately at noon. But by placing the gnomon on a horizontal or half-spherical face with incremental markings, the sundials predicted time fairly accurately all day long throughout the year.
The hemicycle, a more accurate sundial, was built upon their knowledge of geometry. A block of stone in a half-bowl shape had a rod attached to one end whose shadow, depending on the season, cast a circular arc with varied length. The arcs were divided into twelve to indicate the length of each day. The rod, by the way, is called a gnomon. The word comes from the late Greek gignoskein which means to come to know. And so does the word gnostic, come to think. So, in coming to know that shadows measured this way is an indicator of time, sundials and shadow clocks became the standard timekeepers in our lives.
Sundials took all manner of shapes and sizes through history. Even several well-known obelisks around the world are actually gnomon. The Washington Monument is one such example. This map shows the layout of the Washington Monument dial to scale. The declination lines are for the Fourth of July and February 22 and the Spring/Fall Equinox.
The age of the sundial lasted well into the 19th century. Though they’ve been replaced as the main timekeepers of society, they’re still in use. Knowing they’re out there in all shapes and sizes makes me want to go on a treasure hunt to find them. But then that’s just me. 😀
Cool site showing where you can find sundials in the USA and a few elsewhere.
North American Sundial Society
A British society
This site has descriptions of sundials from around the world.
http://www.sundials.co.uk/ A little digging here and you’ll find sundial mottoes. They have an even larger Latin list too. http://www.sundials.co.uk/mottoes.htm
A french site with weird sundials from around the world
Very interesting explanation of sun placement and different types of sundials and shadow clocks. An introduction for the classroom by Lawrence E. Jones
Tomorrow ~ letter T
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