{"id":118,"date":"2015-10-23T00:54:59","date_gmt":"2015-10-23T00:54:59","guid":{"rendered":"http:\/\/theperihelioneffect.com\/?p=118"},"modified":"2017-12-18T19:29:24","modified_gmt":"2017-12-18T19:29:24","slug":"gnomon","status":"publish","type":"post","link":"https:\/\/theperihelioneffect.com\/gnomon\/","title":{"rendered":"Gnomon is the part of a sundial that casts the shadow"},"content":{"rendered":"

Gnomon<\/h1>\n
\"220px-Sundial_Taganrog\"<\/a> \"220px-Gnomon_normalized\"<\/a><\/div>\n

A\u00a0gnomon<\/b>\u00a0([\u02c8no\u028am\u0252n], from\u00a0Greek<\/a>\u00a0\u03b3\u03bd\u03ce\u03bc\u03c9\u03bd<\/span>,\u00a0gn\u014dm\u014dn<\/i>, literally: “one that knows or examines”[1]<\/span><\/sup>[2]<\/span><\/sup>) is the part of a\u00a0sundial<\/a>\u00a0that casts the\u00a0shadow<\/a>.<\/p>\n

The term has come to be used for a variety of purposes in mathematics and other fields.<\/p>\n

History<\/h3>\n

Anaximander<\/a>\u00a0(610\u2013546 BC) is credited with introducing this\u00a0Babylonian<\/a>instrument to the\u00a0Greeks<\/a>.[3]<\/span><\/sup>\u00a0Oenopides<\/a>\u00a0used the phrase\u00a0drawn gnomon-wise<\/i>\u00a0to describe a line drawn perpendicular to another.[4]<\/span><\/sup>\u00a0Later, the term was used for an\u00a0L<\/b>-shaped instrument like a\u00a0steel square<\/a>\u00a0used to draw right angles. This shape may explain its use to describe a shape formed by cutting a smaller square from a larger one.\u00a0Euclid<\/a>\u00a0extended the term to the plane figure formed by removing a\u00a0similar<\/a>\u00a0parallelogram<\/a>\u00a0from a corner of a larger parallelogram. Indeed, the gnomon is the increment between two successive\u00a0figurate numbers<\/a>, including square and triangular numbers.<\/p>\n

Hero of Alexandria<\/a>\u00a0defined a gnomon as that which, when added to an entity (number or shape), makes a new entity similar to the starting entity. In this sense\u00a0Theon of Smyrna<\/a>\u00a0used it to describe a number which added to a\u00a0polygonal number<\/a>\u00a0produces the next one of the same type. The most common use in this sense is an odd integer especially when seen as a\u00a0figurate number<\/a>\u00a0between\u00a0square numbers<\/a>.<\/p>\n

The\u00a0Chinese<\/a>\u00a0used the gnomon. It is mentioned in the 2nd century\u00a0Nine Chapters on the Mathematical Art<\/a><\/i>\u00a0as being used much earlier by the\u00a0Duke of Zhou<\/a>\u00a0(11th century BC).<\/p>\n

Orientation<\/h3>\n

In the\u00a0northern hemisphere<\/a>, the shadow-casting edge of a sundial gnomon is normally oriented so that it points north and is parallel to the rotation axis of the\u00a0Earth<\/a>. That is, it is inclined to the horizontal at an\u00a0angle<\/a>\u00a0that equals the\u00a0latitude<\/a>\u00a0of the sundial’s location. At present, such a gnomon should thus point almost precisely at\u00a0Polaris<\/a>, as this is within a degree of the North\u00a0celestial pole<\/a>.<\/p>\n

On some sundials, the gnomon is vertical. These were usually used in former times for observing the\u00a0altitude<\/a>\u00a0of the\u00a0Sun<\/a>, especially when on the\u00a0meridian<\/a>. 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.<\/p>\n

A three-dimensional gnomon is commonly used in\u00a0CAD<\/a>\u00a0and\u00a0computer graphics<\/a>\u00a0as an aid to positioning objects in the\u00a0virtual world<\/a>. By convention, the X axis direction is colored red, the Y axis green and the Z axis blue.<\/p>\n

NASA<\/a>\u00a0astronauts used a gnomon as a photographic tool to indicate local vertical and to display a color chart when they were working on the Moon’s surface.<\/p>\n

In popular culture<\/h3>\n

In the book\u00a0The Tower at the End of the World<\/i>\u00a0by\u00a0Brad Strickland<\/a>, a giant\u00a0tower<\/a>\u00a0and thin stairs turn out to be the gnomon of a giant sundial. The island the tower is found on is often called “Gnomon Island”.<\/p>\n

The\u00a0Gnomon of Saint-Sulpice<\/a>\u00a0inside the church of\u00a0Saint Sulpice<\/a>\u00a0in\u00a0Paris, France<\/a>, built to assist in determining the date of\u00a0Easter<\/a>, was fictionalized as a “Rose Line<\/a>” in the novel\u00a0The Da Vinci Code<\/a><\/i>.[5]<\/span><\/sup><\/p>\n

A gnomon is used metaphorically in Charles Portis’s novel\u00a0Masters of Atlantis<\/i>.<\/p>\n

Footnotes References<\/h3>\n