Analemmatic sundials are a familly of sundials where the style is mobile and must be displaced according to the date. An analemmatic sundial is composed of a large ellipse and a date line in its middle.
The most common analemmatic sundial is horizontal. It is often drawn on the ground, large enough so a person standing on the sundial and rising his arm vertically plays the role of the style.
It must be noted that the time it is not given by the shadow itself, but by the direction of the shadow prolongated to the ellipse.
The first analemmatic sundial installed in France, and probably in the world, is before the Brou's abbey, near Bourg-en-Bresse. It was installed in 1513 and it has been described in 1644 by Vauzelard who is considered as the inventor and theorician of this type of sundial. Few analemmatic sundials have been built before the twentiest century (Dijon 1827, Besanšon 1902, Montpellier, Avignon).
In an analemmatic sundial, the style is straight and perpendicular to the sundial. Time is read by moving the style along a date line at the center of the ellipse ; the must be placed depending on the date. The date line must therefore be made of a groove where the style can slide, or a series of holes where the style can be stuck.
If the shadow of the style is long enough to cut the ellipse, the time is read at the intersection of the shadow and the ellipse. In case the shadow is too short and does not cut the ellipse, the shadow line must be prolongated to the ellipse (see below).
Correct way to read the time: the shadow is prolongated to the ellipse
Wrong way to read the time: using the shadow's end and read the time from the center of the dial
Note: only the solar time can be drawn on an analemmatic sundial. Therefore, the dialog "Indications given by the sundialquot; is not available.
When the latitude is high, the ellipse tends to a circle and the date line becomes shorter. At the pole, the analemmatic sundial becomes an equatorial sundial. At the equator, the ellipse is reduced to a straight line graduated by the hour points, and the date line reaches its higher length.
Analemmatic sundials are available only for Shadows Expert and Shadows Pro users.