The North American Sundial Society (NASS) was founded in 1994 to give those interested in sundials as more than a mere garden ornament "an opportunity to learn, to interact, and to exchange ideas and information." NASS fondly recalls the time "not that long ago, when an appreciation of dials and their various forms was an integral part of the scientific and mathematical training of any well-educated person" and also publishes a quarterly journal and holds an annual conference.

Ever hear of mass dials? They are a form of sundial, used in Medieval times to mark the time of services. They are usually found on south-facing church walls. Peter R Hamilton-Leggett of the British Sundial Society has this article on mass dials.

If you want a thorough explanation of the equation of time, you can get it from physicist Dr. Art Carlson at the Max Planck Institute for Plasma Physics.

A very advanced form of portable sundial is the astrolabe, which was used to show how the sky looks at a specific place at a given time. This is done by drawing the sky on the face of the astrolabe and marking it so positions in the sky are easy to find. This allows a great many astronomical problems to be solved in a very visual way. Typical uses of the astrolabe include finding the time during the day or night, finding the time of a celestial event such as sunrise or sunset and as a handy reference of celestial positions. Astrolabes were also one of the basic astronomy education tools in the late Middle Ages.


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