analemmatische

Analemmatic sundials, also called analemmatic dials, are a type of sundial in which the hour markings lie along an ellipse on a plane surface rather than along a straight line. The gnomon, a vertical rod or pin, is placed on a movable north–south line at the position corresponding to the Sun’s declination for the day. By repositioning the gnomon along this central axis, the shadow’s intersection with the ellipse indicates the local solar time for any hour.

Construction and operation rely on the geometry of an ellipse. The hour marks are arranged along the ellipse so that each point corresponds to a specific solar hour. The ellipse is sized and oriented for the observer’s latitude, and its major axis is typically aligned roughly east–west while the minor axis runs north–south. To use the dial, the observer places the gnomon at the appropriate position on the central north–south line according to the day of the year; as the sun moves through the sky, the gnomon’s shadow falls on the ellipse at the corresponding hour line, yielding the time.

Origins and use: Analemmatic designs have been described in comparative sundial literature since the early modern period and are widely built for educational purposes and garden installations. The term derives from analemma, reflecting the relationship between the sun’s declination over the year and the dial’s movable gnomon position. Compared with fixed-gnomon sundials, analemmatic models emphasize geometric intuition and latitude-specific calibration.