Claude Hartman claims that an analemmatic sundial is the projection of a polar sundial (the dial plate is set along the East-West direction and inclines so that it is parallel with the polar axis).
It will be easier to explain why a vertical person or staff casts a shadow to the hour points on an ellipse if you assume that an analemmatic sundial is the projection of a equatorial sundial and that his date line is the projection of the style. The date is the projection of a point on the style and the person or staff is the projection line for that point. See on the website of Frans Maes The principle of the analemmatic dial The sundial offers more educational opportunities than a pole style sundial. You can indicate the hours of sunrise and sunset for a specific date (with the "Lambert circle"). You can prove that the sun, radiating from a specific direction (above a tree or above a chimney on a building) has this position on a different time, depending on the date,. On the basis of the shadow on a photograph, taken on a given day, you can determine the time of photographing, by thinking on a analemmatic sundial to the photograph (an application for the police or for a detective !) Willy Leenders Hasselt in Flanders (Belgium) Visit my website about the sundials in the province of Limburg (Flanders) with a section 'worth knowing about sundials' (mostly in Dutch): http://www.wijzerweb.be Op 23-apr-2011, om 21:24 heeft Claude Hartman het volgende geschreven: > I would like to question the instructional qualities of analemmatic sundials. > > Unlike Tony Moss' 'Multi-dial', it is my view that there is only one > relationship easily illustrated - the projection of a polar dial on to a > horizontal surface is an ellipse with corresponding hour points. > I am afraid that the instruction falls into rote learning of procedure like > so many sundial kits (and much of pedagogy). I do not know what the > underlying motivation was for "that part of the UK National Curriculum". I > assume it was to understand something of the natural world and not to acquire > the skill of making a sundial. Under that assumption I think the analemmatic > falls short and could produce confusion for inquiring minds. > > With that said I certainly would NOT join any ban on such dials as "dangerous > for children"! Indeed, both children and adults interact with them quite > well and they can make a beautiful asset in a school. However, expect > difficulty with a persistent inquiring person seeking explanations. > > Perhaps someone on this list can show me a way to explain that to anyone > lacking much geometric skill such as a 10 year old (or me). > > Claude Hartman > (retired science teacher basking in the sunshine of 35 N, 120 W) > > > --------------------------------------------------- > https://lists.uni-koeln.de/mailman/listinfo/sundial >
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