# gnomon

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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.

## Gnomon

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.

## gnomon

[′nō·mən]
(engineering)
On a sundial, the inclined plate or pin that casts a shadow. Also known as style.
(mathematics)
A geometric figure formed by removing from a parallelogram a similar parallelogram that contains one of its corners.
References in periodicals archive ?
An Indian circle is a circle drawn on the ground, of an arbitrary radius, at the center of which a gnomon is installed.
Zum antiken astro-geodatischen Messinstrument Skiotherikos Gnomon," Zeitschrift far Vermessungswesen 130.
We'll need to do some counting similarly to the triangular numbers but with a pentagonal grid of dots and develop a table of values that correspond to each "level" of number similar to the last edition of Diversions and identify the gnomon sequence.
In the Square, successive gnomons were 3, 5, 7, 9, 11, 13, 15.
Explanation could refer to differences increasing by one each time so the gnomons are the counting numbers 2, 3, 4, 5, 6, 7, 8 (revisiting this next issue).
In Imperial China the emperor's astronomers determined the date of the winter solstice and length of the year with respectable precision by measuring the noon shadow of a gnomon.
If you already have a tower, you don't need another gnomon.

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