What is the word for the upright shadow-casting part of a sundial?
Sundial broad shadow; the shadow of the style shows the time. The gnomon may be a rod, wire, or elaborately decorated metal casting. The style must be parallel to the axis of the Earth's rotation for the sundial to be accurate throughout the year. The style's angle from horizontal is equal to the sundial's geographical latitude. In a broader sense, a sundial is any device that uses the Sun's altitude or azimuth (or both) to show the time. In addition to their time-telling function, sundials are valued as decorative objects, literary metaphors, and objects of mathematical study. It is common for
Sundial Biancani's "Constructio instrumenti ad horologia solaria" (ca. 1620) discusses how to make a perfect sundial. They have been commonly used since the 16th century. In general, sundials indicate the time by casting a shadow or throwing light onto a surface known as a "dial face" or "dial plate". Although usually a flat plane, the dial face may also be the inner or outer surface of a sphere, cylinder, cone, helix, and various other shapes. The time is indicated where a shadow or light falls on the dial face, which is usually inscribed with hour lines. Although usually straight, these hour