This gnomon is like those used on the lunar surface by Apollo astronauts during their scientific and photographic tasks. A gnomon is a gimbaled stadia rod mounted on a tripod so that the rod was free to point vertically. When deployed on the lunar surface, the shadow cast by the staff indicated sun angle and, therefore, direction. The rod length and the painted scale provided a reference for estimating the sizes of nearby objects. Shades of gray on the rod ranged in reflectivity from 5% to 35% and a color scale enabled more accurate determination of rock and soil colors by comparison.
