Analemmatic sundials belong to a familly of elliptical sundials with mobile style. The style is moved to a position depending on the current date, on a date line in the middle of the sundial. The style casts a shadow that points towards a hour mark on a large ellipse.
History and principle
The first analemmatic sundial installed in France, and probably in the world, is at the church of Brou, close to Bourg-en-Bresse, in 1513. It was described in 1644 by Vauzelard who is considered as the inventor and theorician of analemmatic sundials.
In a classic analemmatic sundial, the style is perpendicular to the ellipse. The style must be placed on the date line at the position corresponding to the current date. The shadow of the style is extended to the ellipse where points mark hours.
Analemmatic sundials are usually installed in parks where the large ellipse is drawn on the ground. A person then stands on the date line with the hand raised above him to cast a shadow on the ellipse.
Analemmatic sundials are not always horizontal and can be vertical, declining or even reclining.
Analemmatic sundial of Montpellier, France
Two analemmatic sundial layouts, for the city of Lisbon (Portugal), drawn with Shadows.
Left: horizontal analemmatic with the shadow of the style drawn for January 30th at 10h15 of solar time.
Right: vertical declining by 30° towards East, with the shadow of the style drawn for May 20th, at 13h15 of solar time.
Page of the online help of Shadows analemmatic sundials
- top banner: stone sundial made by John Carmichael, www.sundialsculptures.com.
- Montpellier: photo FB
- date line (left): John Carmichael, www.sundialsculptures.com.
- date line (right): analemmatic sundial of the Westminster Abbey in London, photo FB.
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