Sunrise, Sunset... 8.4k

      I found a really fantastic Astronomy program, RedShift® 2 from Maris, which ultimately led me to wonder if I could use its Ephemeris report data for the sun's position throughout the year to design and build a highly accurate sundial. Using RedShift, Microsoft Excel, and AutoSketch, I developed the design for a simple and very accurate universal equatorial sundial with an analemmic gnomon. It indicates the exact time every minute of the day; it indicates the exact date every day of the year, and it even quickly adjusts for Daylight Saving Time!

      I built my first sundial out of 1/4" brass (127k.jpg). It is about 26" x 14" x 14".

      The sundial is universal because it will work at any location on the Earth. It is an equatorial design because time is indicated where the shadow falls on a dial ring which lays parallel to the earth's equator. The shadow-casting device, an analemmic gnomon plate (118k.jpg), rather than being a straight edge or rod, is actually a plate which has a "figure-8" pattern cut out of the middle. This figure-8 cutout describes the apparent motion of "the sun about the Earth" throughout the year.

      The sun does not appear in the same position in the sky at a given time of day (for example, noon) throughout the 365 days of the year. Due to the tilt of the Earth's axis and the elliptical orbit of the Earth about the sun, at a single specified time daily throughout the year the sun actually appears to move along an annual figure-8 path through the sky. Thus, when marked at the same time every day, e.g. noon, the shadow from a fixed object similarly follows this annual figure-8 path along the ground. The shape of the annual path of this shadow is called an analemma. The fact that this annual path is a figure-8, and not just a straight line north and south, is the reason that most conventional sundials are innacurate by as much as 14 minutes slow to 16 minutes fast during different times of the year. For those interested in a more detailed explanation of the analemma, the website analemma.com provides a much better description.

      In this sundial it is desired that the shadow always falls on a single point (time mark) on the dial's timeline at that single precise time every day throughout the year. Thus, the pattern in this sundial's analemmic gnomon plate describes the apparent figure-8 path the sun follows annually in the sky above the fixed time point. The analemmic gnomon plate is mounted so that it can swivel to directly face the sun above every time point on the sundial, making this sundial useful and accurate at any time during the day, every day of the year.

      The months and days of the year are engraved around the perimeter of the analemmic gnomon's figure-8 cutout. By running your finger above the inside edge of the cutout you can determine the exact date... when the edge of the shadow from your finger falls on the time line on the equatorial dial, then the edge of your finger is directly over the current date on the gnomon.

      I was very proud of this first design and applied for a patent on it in 1997. Later I learned from Mr. Fred Sawyer, then President of the North American Sundial Society, that a similar sundial had already been patented by Mr. Lloyd Mifflin of Germantown, Pennsylvania in 1867. It's kind of funny... after finding this out I then received a Notice of Allowance from the U.S. Patent Office stating that my application had been approved in its entirety and that for a mere $4,000 more they would be happy to issue me a patent for this invention! Needless to say, I didn't spend the $4,000 and I learned a valuable lesson about the USPTO and the potential worth of patents.

      I also designed this 6' x 4' x 4' stainless steel sundial sculpture (277k.jpg), which was placed in Boise's Ann Morrison park this spring. I really like this design for its simplicity, and because it visually demonstrates very clearly the apparent motion of the sun "about" the earth throughout the day and the year. It indicates the time and date literally to within seconds, and also adjusts for Daylight Saving Time!

      JST Fabrication, an excellent stainless steel shop here in Boise, generously donated all materials, their shop and most of the labor to build the Ann Morrison Park sundial. JST has a wonderful manufacturing facility, complete with a computer-numerical-controlled (CNC) CO2 laser. They converted my CAD drawing files for this sundial into a CNC program for their laser, and then used it to cut and etch all the stainless steel material and markings with incredible precision! Now that they have the CNC program, they are prepared to build more of these in similar designs and sizes. If you would like a similar custom dial for your area, please e-mail me at the address below. I will be happy to discuss this further with you!

      I would like to eventually have quantities of these cast in bronze or verdigris aluminum in smaller sizes and prices more suitable for homes and gardens, but these will not be available for several years still.

      For those who are interested in building a similar sundial for your own personal use, I do have a page which describes the method and calculations I used to derive my first dial. You are certainly welcome to use this information.

Tempus captum!

Pete Swanstrom
5115 W. Wymosa St.
Boise, ID. 83703

Phone (208) 283-1163

Last Updated: August 17, 2018
Send Mail to: pete@swanstrom.net
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