analemmatisch

Analemmatisch, in English often rendered as analemmatic, describes a class of sundials designed around the analemma, the figure-eight path of the Sun observed from a fixed location over a year. The name emphasizes the use of the Sun’s changing declination and the corresponding yearly shift in shadow.

A typical analemmatic dial is laid out on a horizontal surface. The hour lines lie on an ellipse whose major axis runs east–west. At a given latitude, the ellipse’s semi-minor axis is proportional to the major axis by the factor cos(latitude). For each hour relative to solar noon, a point on the ellipse is defined by coordinates x = a sin(H) and y = b cos(H), and these points are connected to form the hour lines. The resulting dial shows solar time rather than clock time, and must be read with attention to local apparent solar noon.

A distinctive feature of analemmatic dials is the movable gnomon. Instead of a fixed vertical rod, the base of the gnomon sits on a central north–south line through the ellipse. To use the dial on a given day, the gnomon is placed at the position along that line that corresponds to the Sun’s declination for that date. When the sun is at its noon position, the gnomon’s shadow falls along the appropriate hour line, allowing time to be read from the ellipse.

Analemmatic dials are valued for their instructional clarity, showing directly how latitude, the Sun’s path, and time are interconnected. They are commonly built in educational settings and as decorative garden sundials, with construction requiring accurate orientation and latitude information.