scaphe

A scaphe is a type of sundial that tells time by the shadow cast by a gnomon onto a curved surface. This curved surface, often a part of a sphere or cylinder, is specifically designed to show the hours of the day. Unlike a horizontal or vertical sundial, the scaphe's concave face allows for a more accurate and often more visually appealing representation of time's passage. The shadow-casting object, the gnomon, is typically a straight rod.

The design of a scaphe is based on the principle that the sun's apparent motion across the sky traces a path that can be mapped onto a curved surface. The curvature is crucial for ensuring that the hour lines are evenly spaced, or spaced according to a specific diurnal curve, throughout the day. This contrasts with flat sundials where hour lines can become compressed at certain times of the day due to perspective.

Scaphes were popular in antiquity and the Renaissance, with many sophisticated examples created by astronomers and artisans. Their construction often required precise calculations to ensure accuracy. The term "scaphe" itself comes from the Greek word for "hollow" or "cup," referring to the characteristic curved dial. While less common today than simpler sundial forms, the scaphe remains an elegant and historically significant instrument for measuring time.