Gnomon

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Gnomon

The gnomon is the part of a sundial

Sundial

A sundial is a device that measures time by the position of the Sun. In common designs such as the horizontal sundial, the sun casts a shadow from its style onto a flat surface marked with lines indicating the hours of the day....
that casts the shadow

Shadow

File:Shadow, Ronald Reagan Building - Washington, D.C..jpgA shadow is an area where direct light from a light source cannot reach due to obstruction by an object....
. Gnomon (???µ??) is an ancient Greek

Ancient Greek

Ancient Greek is the historical stage in the development of the Greek language spanning across the Archaic Greece , Classical Greece , and Hellenistic civilization periods of ancient Greece and the classical antiquity....
word meaning "indicator", "one who discerns," or "that which reveals."
idea of enlarging yet preserving the shape was considered quite profound.

he northern hemisphere

Northern Hemisphere

The Northern Hemisphere is the half of a planet that is north of the equator?the word sphere literally means 'half sphere'. It is also that half of the celestial sphere north of the celestial equator....
, the shadow-casting edge is normally oriented so that it points north

North

North is one of the four cardinal directions, specifically the direction that, in Western culture, is treated as the fundamental direction:...
and is parallel to the rotation axis of the Earth

Earth

Earth is the third planet from the Sun. Earth is the largest of the terrestrial planets in the Solar System in diameter, mass and density. It is also referred to as the World and Wiktionary:Terra.Note that by International Astronomical Union convention, the term "Terra" is used for naming extensive land masses, rather...
.

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The gnomon is the part of a sundial

Sundial

Shadow

Ancient Greek

History of the term

Anaximander
Anaximander

Anaximander was a pre-Socratic Ancient Greece philosopher who lived in Miletus, a city of Ionia. He belonged to the Milesian school and learned the teachings of his master Thales....
(610–546 BC) is credited with introducing this Babylonian instrument to the Greeks
Greeks

The Greeks , also known as Hellenes, are a nation and ethnic group native to Greece, Cyprus and neighbouring regions, who can also be found in Greek diaspora communities around the world....
. The Chinese
China

China is a Culture of China, an ancient civilization, and, depending on perspective, a national or multinational entity extending over a large area in East Asia....
also used the gnomon, mentioned in the 2nd century Nine Chapters on the Mathematical Art as being used much earlier by the Duke of Zhou
Duke of Zhou

The Gong of Zhou was the brother of King Wu of Zhou in ancient China. Only three years after defeating the Shang Dynasty King Wu died, leaving the task of consolidating the dynasty's power to the Duke of Zhou....
(11th century BC).
Oenopides
Oenopides

Oenopides of Chios was an ancient Greece mathematician and astronomer, who lived around 450 Common Era. He was born shortly after 500 BC on the island of Chios, but mostly worked in Athens....
used the phrase drawn gnomon-wise to describe a line drawn perpendicular to another.
Later, the term was used for an L-shaped instrument used to drawing right angles. This shape may explain its use to describe
the shape formed by cutting a smaller square from a larger one.
Euclid
Euclid's Elements

Euclid's Elements is a mathematics and geometry treatise consisting of 13 books written by the Greek mathematics Euclid in Alexandria circa 300 BC....
extended the term to the plane figure formed by removing a similar
Similarity (geometry)

Two geometrical objects are called similar if they both have the same shape. Equivalently and more precisely, one is congruence to the result of a uniform Scaling of the other....
parallelogram
Parallelogram

In geometry, a parallelogram is a quadrilateral with two sets of parallel sides. The opposite or facing sides of a parallelogram are of equal length, and the opposite angles of a parallelogram are of equal size....
from a corner of a larger parallelogram.
Hero
Hero of Alexandria

Hero of Alexandria . was an ancient Greek mathematics who was a resident of a Roman province ; he was also an engineer who was active in his hometown of Alexandria....
defined a gnomon as that which added to anything, number or figure, makes the whole similar to what was added.
In this sense Theon of Smyrna
Theon of Smyrna

Theon of Smyrna was a Greece philosopher and mathematician, whose works were strongly influenced by the Pythagoras school of thought. Little is known about the early life of Theon of Smyrna; Ptolemy cites work of his on several occasions between 127 and 132, but there are few other dates that are known for certain....
used it to describe a number which added to a polygonal number produces the next one of the same type.
The most common use in this sense is an odd integer especially when seen as a figurate number
Figurate number

A figurate number is a number represented as a regular and discrete geometry pattern such as a polygonal number or a polyhedral number....
between square numbers.

The idea of enlarging yet preserving the shape was considered quite profound.

In a recent book Gazalé, Midhat J.
Midhat J. Gazalé

Midhat Gazal? is an international telecommunications and space consultant and was a visiting Professor of Telecommunications and Computer Management at the University of Paris IX....
coined the term gnomonicity as a synonym for the 20th century idea of Self-similarity
Self-similarity

In mathematics, a self-similar object is exactly or approximately similarity to a part of itself . Many objects in the real world, such as coastlines, are statistically self-similar: parts of them show the same statistical properties at many scales....
both in the increasing and decreasing scale as in fractals.

Also

In the northern hemisphere

Northern Hemisphere

North

North is one of the four cardinal directions, specifically the direction that, in Western culture, is treated as the fundamental direction:...
and is parallel to the rotation axis of the Earth

Earth

Angle

In geometry and trigonometry, an angle is the figure formed by two Ray sharing a common endpoint, called the vertex of the angle . The magnitude of the angle is the "amount of rotation" that separates the two rays, and can be measured by considering the length of circular arc swept out when one ray is rotated about the vertex to coincide...
that equals the latitude

Latitude

Latitude, usually denoted symbolically by the Greek letter phi gives the location of a place on Earth north or south of the equator. Lines of Latitude are the horizontal lines shown running east-to-west on maps ....
of the sundial's location. On some sundials, the gnomon is vertical. These were usually used in former times for observing the altitude

Altitude

Altitude has multiple uses depending on the context in which it is used . As a general definition, altitude is a distance measurement, usually in the vertical or "up" direction, between a reference datum and a point or object....
of the Sun

Sun

The Sun , a G V star, is the star at the center of the Solar System. The Earth and other matter orbit the Sun, which by itself accounts for about 98.6% of the Solar System's mass....
, especially when on the meridian

Meridian (geography)

A meridian is an imaginary arc on the Earth's surface from the North Pole to the South Pole that connects all locations running along it with a given longitude....
. The style is the part of the gnomon that casts the shadow. This can change as the sun moves. For example, the upper west

West

West is most commonly a noun, adjective, or adverb indicating Direction or geography.West is one of the four cardinal directions or compass points....
edge of the gnomon might be the style in the morning and the upper east edge might be the style in the afternoon.

The art of constructing a gnomon sundial is sometimes termed gnomonics. One so skilled would be referred to as a gnomonist.

Gnomon may also imply the design paradigm

Design paradigm

Design paradigms are Model , archetypes, or quintessential examples of designed solutions to problems. The term "Design paradigm" is used within the design professions, including architecture, industrial design and engineering design, to indicate an archetypal solution....
relationship between an indicator and a dial or other reference, as with a speedometer

Speedometer

A speedometer is a device that measures the instantaneous speed of a land vehicle.Now universally fitted to motor vehicles, they started to be available as options in the 1900s, and as standard equipment from about 1910 onwards....
and needle. In this case, the needle functions as a gnomon against the incremented speedometer background.

Also, gnomon is the name given to an aesthetic process utilized by James Joyce

James Joyce

James Augustine Aloysius Joyce was an Ireland expatriate author of the 20th century. He is best known for his landmark novel Ulysses and its controversial successor Finnegans Wake , as well as the short story collection Dubliners and the semi-autobiographical novel A Portrait of the Artist as a Young Man ....
in his set of short stories Dubliners
Dubliners

Dubliners is a collection of 15 short stories by James Joyce, first published in 1914. The fifteen stories were meant to be a naturalistic depiction of the Ireland middle class life in and around Dublin in the early years of the 20th century....
, whereby the whole of the character is revealed by a single part.

In popular culture

In the book The Tower at the End of the World, written by Brad Strickland

Brad Strickland

William Bradley Strickland is an United States author known primarily for his fantasy and science fiction. He was born in New Holland, Georgia, Georgia ....
, an island

Island

An island or isle is any piece of land that is surrounded by water. Very small islands such as emergent land features on atolls are called islets....
with a giant tower

Tower

Towers are tall human-made structures that are always taller than they are wide, usually by a significant margin. Towers are generally built to take advantage of their height, and can stand alone or as part of a larger structure....
and thin stairs is found on a lake

Lake

A lake is a terrain feature , a body of liquid on the surface of a world that is localized to the bottom of basin and moves slowly if it moves at all....
. The tower and stairs, along with the odd sculpture

Sculpture

Sculpture is Three-dimensional space artwork created by shaping or combining hard and or plastic material, sound, and or text and or light, commonly Stone sculpture , metal, glass, or wood....
s surrounding it, are later discovered to be a giant sundial, with the tower and stairs being the gnomon. The island the tower is found on is often called "Gnomon Island".

A gnomon inside the church of Saint Sulpice

Saint-Sulpice (Paris)

Saint-Sulpice is a famous Parisian church on the east side of the Place Saint-Sulpice, in the Luxembourg Quarter of the VIe arrondissement. At 113 meters long, 58 meters in width and 34 meters tall, it is only slightly smaller than Notre Dame de Paris and thus the second largest church in Paris....
in Paris, France, built to assist in determining the date of Easter

Easter

Easter is the most important religious feast in the Christianity liturgical year.Christians believe that Jesus was Resurrection of Jesus from the dead three days after his Crucifixion of Jesus, and celebrate this resurrection on Easter Day or Easter Sunday , two days after Good Friday....
, was incorrectly identified as a "Rose Line

Rose Line

Rose Line is a name given to the Paris Meridian in the Priory of Sion mythology and popularized by Dan Brown in his novel The Da Vinci Code....
" in Dan Brown

Dan Brown

Dan Brown is an United States author of thriller fiction, best known for the 2003 bestselling novel, The Da Vinci Code and the 2000 bestselling novel, Angels & Demons....
's novel The Da Vinci Code
The Da Vinci Code

The Da Vinci Code is a 2003 in literature Mystery -detective fiction fiction novel written by United States author Dan Brown and published by the Doubleday in the United States and Bantam Books in the United Kingdom....
.

NASA Astronauts used a gnomon as a photographic tool to indicate local horizon and to display a color chart when they were working on the Moon's surface.

Gnomon

History of the term

Also

In popular culture

Footnotes