Frequently Asked Questions
about Sundials
Hosted by Bob Terwilliger
about Sundials
Hosted by Bob Terwilliger
1. What is a sundial and how do they work?
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Books to read
- Albert Waugh: Sundials, Their Theory and Construction
- Waugh is perhaps the best "first book", but it uses logarithms in the computations - simply ignore them.
- Newton and Margaret Mayall: Sundials: Their Construction and Use
- René Rohr: Sundials: History, Theory, and Practice
- Somewhat advanced
Web Sites - What is a Sundial? - The Franklin Institute Online
- Sundials - Sundial history From the National Institute of Standards and Technology
- A Glossary of Sundial Terms - By John Davis
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2. How can I make my own sundial?
- All the Books to Read include instructions for making sundials.
- Before you start
- Some simple trigonometry for a horizontal dial
- Use
DeltaCad, a simple and inexpensive shareware CAD program.
You can download special special programs or "Macros" which will produce a variety of dials.
- How long should my gnomon be?
- Special Software for making Sundials
A note on materials: For anything in metals you would have to explore for sources, but for ordinary projects, you can probably get weather-proof boards similar to plywood from your local sign shop. They might also be able to provide durable vinyl numerals etc. which can be custom made from computer files.
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3. I have a sundial. How do I set it up?
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There are two steps to setting up a sundial
- Check your dial, and align it to True North - Although there are exceptions, most common dials must be oriented with regards to north
- Correcting a dial to your latitude - Assumes a commercial mass produced dial.
- Can I just twist my dial for Daylight Savings Time?
In general, it won't work for most common horizontal sundials.
If you have a bowstring equatorial, or similar dial, you may be able to
rotate the shadow receiving surface 15º, or one hour, toward the east.
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4. Why doesn't my sundial tell clock time?
- The latitude correction
- The longitude correction (time zone offset)
- The Equation of Time
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7. What is the best way to buy a sundial?
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In order to be a true solar timekeeper, a sundial should be made specifically for the location where it is going to be used. Avoid the mass produced commercial horizontal dials available from landscape and gardening supply houses. Some commercial bow-string equatorial dials can be adapted to your location. Find out before you buy.
See the question I have a sundial. How do I set it up? in this FAQ for some of the problems with mass produced horizontal dials. Some of these dials are not even laid out correctly and will not function under any circumstances.
Makers who will custom design and build a sundial for you can be found here on the NASS Links page Click on Artisans in the left frame.
Or... Make your own, and join the fascinating world of Dialing!
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8. More advanced questions
- What is the Equation of Time?
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