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gnomon(nō`mŏn): see sundialsundial,
instrument that indicates the time of day by the shadow, cast on a surface marked to show hours or fractions of hours, of an object on which the sun's rays fall.
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gnomon(noh -mon) A device used in ancient times to measure the altitude of the Sun and hence to determine the time of day and time of year. It consisted of a vertical shaft of known height (such as an upright rod or pillar) that cast a shadow of measurable length and direction on a graduated horizontal base. The ratio of height to shadow length gave the tangent of the altitude angle. The term is also applied to the metal projection on a sundial, used for the same purpose.
an ancient astronomical instrument consisting of a vertical column on a horizontal platform. The altitude and azimuth of the sun can be determined from the length and direction of the column’s shadow. The shortest shadow during the day indicates the direction of the north line. In ancient times the gnomon was used to determine the inclination of the ecliptic to the equator and the geographical latitude of locations. In modern times the gnomon finds use only as a sundial.