Gnomon
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A gnomon (. The term is used for a variety of purposes in mathematics and other fields.
History
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A painted stick dating from 2300 BC that was excavated at the archeological site of Taosi is the oldest gnomon known in China.[4] The gnomon was widely used in ancient China from the second millennium BC onward in order to determine the changes in seasons, orientation, and geographical latitude. The ancient Chinese used shadow measurements for creating calendars that are mentioned in several ancient texts.[citation needed]
According to the collection of Zhou Chinese poetic anthologies Classic of Poetry, one of the distant ancestors of King Wen of the Zhou dynasty used to measure gnomon shadow lengths to determine the orientation around the 14th century BC.[5][6] The ancient Greek philosopher Anaximander (610–546 BC) is credited with introducing this Babylonian instrument to the Ancient Greeks.[7]
The ancient Greek mathematician and astronomer Oenopides used the phrase drawn gnomon-wise to describe a line drawn perpendicular to another.[8] Later, the term was used for an L-shaped instrument like a steel square used to draw right angles. This shape may explain its use to describe a shape formed by cutting a smaller square from a larger one. Euclid extended the term to the plane figure formed by removing a similar parallelogram from a corner of a larger parallelogram. Indeed, the gnomon is the increment between two successive figurate numbers, including square and triangular numbers.[citation needed]
Definition of Hero of Alexandria
The ancient Greek mathematician and engineer
Vitruvius
Pinhole gnomons
Perforated gnomons projecting a pinhole image of the Sun whose location can be measured to tell the time of day and year were described in the Chinese
In the Middle East and Europe, it was separately credited to the Egyptian astronomer and mathematician
Orientation
In the Northern Hemisphere, the shadow-casting edge of a sundial gnomon is normally oriented so that it points due northward and is parallel to the rotational axis of Earth. That is, it is inclined to the northern horizon at an angle that equals the latitude of the sundial's location. At present, such a gnomon should thus point almost precisely at Polaris, as this is within 1° of the north celestial pole.
On some sundials, the gnomon is vertical. These were usually used in former times for observing the altitude of the Sun, especially when on the meridian. The style is the part of the gnomon that casts the shadow. This can change as the Sun moves. For example, the upper west edge of the gnomon might be the style in the morning and the upper east edge might be the style in the afternoon.
Modern uses
Gnomons have been used in space missions to the Moon and Mars. The gnomon used by the Apollo astronauts was a gimballed stadia rod mounted on a tripod. While the rod's shadow indicated the direction of the Sun, the grayscale paints of varying reflectivity and the red, green and blue patches facilitated proper photography on the surface on the Moon.[12] MarsDials have been used on Mars Exploration Rovers.
In computer graphics
A three-dimensional gnomon is commonly used in CAD and computer graphics as an aid to positioning objects in the virtual world. By convention, the x-axis direction is colored red, the y-axis green and the z-axis blue.
In popular culture
The
Footnotes
- Perseus Project.
- ^ Harper, Douglas. "gnomon". Online Etymology Dictionary.
- ^ Pietrocola, Giorgio (2005). "gnomon collection". Maecla. Retrieved 2020-06-28.
- ISBN 978-1-4614-6141-8.
- ISBN 978-1-4614-6140-1– via NASA ADS.
- ISBN 978-1-4614-6141-8.
- Nine Chapters on the Mathematical Art claims gnomons were used by the Duke of Zhou (11th century BC). Laërtius, Diogenes. "Life of Anaximander". Archived 2017-04-26 at the Wayback Machine
- ^ Heath (1981) pp. 78-79
- ^ The Asiatic Review. 1969.
- ISBN 9780486151700.
- JSTOR 227759.
- ^ "Gnomon, Lunar, Apollo". The Smithsonian Institution, National Air and Space Museum. Retrieved 6 February 2024.
- ^ Sharan Newman, The Real History Behind The Da Vinci Code (Berkley Publishing Group, 2005, p. 268).
References
- ISBN 0-691-00514-1.
- ISBN 9780486240732(first published 1921).
- Laërtius, Diogenes, The Lives and Opinions of Eminent Philosophers, trans. C.D. Yonge. London: Henry G. Bohn, 1853.
- Mayall, R. Newton; ISBN 0-486-41146-X
- Waugh, Albert E., Sundials: Their Theory and Construction, Dover Publications, Inc., 1973, ISBN 0-486-22947-5.