I have not done this, but a few thoughts: I would start by talking (preferably outdoors) about the sun and where it casts a shadow over the course of a day and a year. This is where it is important for the students to develop some understanding. Nothing is gained if at the end the whole thing seems just like 'magic'.
I would not emphasize the layout of dials (advanced topic) but only the fact that a horizontal dial (plate and gnomon) must be designed for the specific latitude. (Anno's book of sundials is wonderful for its pop-ups of horizontal sundials at different latitudes.) And I'd talk about kinds of time (following Waugh) -- just sufficient to explain the need for corrections for equation of time, longitude, and daylight savings time. (My own approach is not explain how the sundial has to be "corrected" to get "watch time" but rather how our "watch time" has to be corrected to get correct local solar time.) Then a bit of a discussion about how to tell a decent dial from a "garden shop" decorative item, and how to install it. And I'd try to have a bunch of good illustrations (and examples) of horizontal dials, to emphasize what elements are necessary to accurate functioning, and what is the scope for artistic creativity. [My own thinking about teaching about dials -- for understanding -- would start with the earth as a sundial, then move to a small globe as a model. Then I would progress to an equatorial dial (as an abstraction of the globe's equatorial plane and the polar axis). All with lots of hands-on models. In a brief lesson I would probably not even get to horizontal dials. If I did talk about a horizontal dial, I would try to demonstrate it as a slice through a cylinder with 15 deg sectors (or equivalently, as a projection on a plane not parallel to the equator).] Good luck! and I look forward to other folks' ideas! Steve Woodbury 38 o 48 ' N 77 o 14 ' W -
