Sundials - World's Oldest Clocks

North American Sundial Society

Compendium_Dec2008_FrontPageThis issue begins with "Sundials for Starters" by Robert Kellogg from Maryland, describing the Cahokia Mounds American Woodhenge built by Mississippian Indians.  Robert then discusses the mathematics of astro-archeology to compute the alignments of the wooden posts for sunrise at summer and winter solstices and at the spring-fall equinox.  During the mathematical investigation Robert exclaims, " Our euphoria at becoming the next Indiana Jones is shattered however when we realize that (1) we have ignored refraction, (2) we've used the center of the sun and may need to use the uppoer or bottom limb of the sun as a realistic, observable marker, and (3) we have ignored the Collinsville Bluffs that rise above the true horizon."  So how do we solve the problem? Read The Compendium and find out.

The Alessandro Gunella from Italy discusses the "Discovery that Lines for Unequal Hours are Not Straight", or at least this was the thinking during the 16th century.  Are they curved or straight? 

Next the Connecticut Historical Society discusses the Sheldon Moore Sundial, a popular dial manufactured in Kennsignton, CT during the 1840's. "The manufacture of sundials was commenced prior to August 1840, in which month, a supply was sent to Breck & Company of Boston for sale at 20% commission.  In six months they sold 18 dials, which apparently encouraged Sheldon Moore to expanc his facilities".  How much did they cost?  Read The Compendium and find out.

John Davis of the UK discusses a Triple Horizontal Dial for California. John starts his article with an introduction "There are not many clients for a horizontal sundial that have consulted an original copy of William Leybourn's 1682 book on dialing before arriving to discuss their dial design.  But Dr. Rudy Light of Redwood Valley, California, had done so and also brought a copy of Leybourn's diagram of 'An Horizontall Dial with its Furniture' ... with him when he visited me in the summer of 2003.  When he explained that he wanted a large scientific dial to position ouside his house and that he 'wasn't aftriad of complications', I knew it would be an interesting project."  The result of the project is on the cover of this issue of The Compendium.

And did you know that The Entrance Exam for Japaneese Junior High School students contains questions about gnomonics?  Could you answer the questions correctly?  See if you qualify for Shibuya Kyoiku Gakuen Makuhari Junior High School, Chiba City, Japan.  Barry Duel, an NASS member interviewed the author of the gnomnics questions to find "The science teacher who made the test explained in an interview that he tries to prepare problems that students cannon easily memorize in advance.  He wants students who can think ..."

Read this issue of The Compendium to find these articles and much, much more.

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Compendium_Dec2002_FrontPageThis issue begins with several articles about shadow sharpeners, the ability to change the penumbral edge of a shadow that is created by the fact that the sun is a disk, not a point, of light.  William Walton from Vermont and Gianni Ferrari from Italy each offer there thoughts and solutions to getting a sharper shadow for reading time more precisely.

Then John Carmichael from Arizona ponders the McMath-Oierce Solar Telescope as a giant sundial gnomon, and then mathematically analyzes what happens if you choose a "fat" gnomon of various shapes such as a cylinder, hexagon, pentagon, square, or triangle.  In the end, John presents the mathematics so that you can accurately draw hour lines on a horizontal dial face given one of these gnomon shapes.

Next, Claude Hartman from California discusses the fundamentals of the Celestial Sphere, and what we mean by the "pole" and "equator".  Then Claude explains those terms used by astronomers and sundialists to define the position of the sun, definining "solar declination" as equivalent to measuring where we are on the earth by latitude and "solar right ascension" as the equivalent of longitude.

Mohammad Begheri from Iran describes the first analemmatic sundial in Iran, starting with "Iran has a long and rich tradition in many branches of astronomy, including gnomonics.  Untial a few decades agon, sundials were used in mosques and madrassas (traditional religious schools) to show the times of the day, especially to determine the times of the five daily ritual prayers."  Read more in The Compendium to find out about the first analemmatic sundial.

Download this file (Compendium_Dec2002.pdf)Compendium_Dec2002.pdf[ ]1929 kB

Four times a year the North American Sundial Society publishes The Compendium, the journal of sundialing.  Edited by Sterve Lelievre, the journal illuminates various aspects of sundials,both new and old.  The Compendium presents sundial mathematics, sundial histories, and sundials of interest since 1994.

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