A sundial is a horological device that tells the time of day when direct sunlight shines by the apparent position of the Sun in the sky. In the narrowest sense of the word, it consists of a flat plate and a gnomon, which casts a shadow onto the dial. As the Sun appears to move through the sky, the shadow aligns with different hour-lines, which are marked on the dial to indicate the time of day. The style is the time-telling edge of the gnomon, though a single point or nodus may be used. The gnomon casts a broad shadow; the shadow of the style shows the time. The gnomon may be a rod, wire, or elaborately decorated metal casting. The style must be parallel to the axis of the Earth's rotation for the sundial to be accurate throughout the year. The style's angle from horizontal is equal to the sundial's geographical latitude.
A gnomon is the part of a sundial that casts a shadow. The term is used for a variety of purposes in mathematics and other fields.
The scaphe was a sundial said to have been invented by Aristarchus of Samos. There are no original works still in existence by Aristarchus, but the adjacent picture is an image of what it might have looked like; only his would have been made of stone. It consisted of a hemispherical bowl which had a vertical gnomon placed inside it, with the top of the gnomon level with the edge of the bowl. Twelve gradations inscribed perpendicular to the hemisphere indicated the hour of the day.
The MarsDial is a sundial that was devised for missions to Mars. It is used to calibrate the Pancam cameras of the Mars landers. MarsDials were placed on the Spirit and Opportunity Mars rovers, inscribed with the words "Two worlds, One sun" and the word "Mars" in 22 languages. The MarsDial can function as a gnomon, the stick or other vertical part of a sundial. The length and direction of the shadow cast by the stick allows observers to calculate the time of day. The sundial can also be used to tell which way is North, and to overcome the limitations of a magnetic north different from a true north.
The Jantar Mantar is a collection of 19 astronomical instruments built by the Rajput king Sawai Jai Singh, the founder of Jaipur, Rajasthan. The monument was completed in 1734. It features the world's largest stone sundial, and is a UNESCO World Heritage Site. It is near City Palace and Hawa Mahal. The instruments allow the observation of astronomical positions with the naked eye. The observatory is an example of the Ptolemaic positional astronomy which was shared by many civilizations.
In geometry, a gnomon is a plane figure formed by removing a similar parallelogram from a corner of a larger parallelogram; or, more generally, a figure that, added to a given figure, makes a larger figure of the same shape.
Analemmatic sundials are a type of horizontal sundial that has a vertical gnomon and hour markers positioned in an elliptical pattern. The gnomon is not fixed and must change position daily to accurately indicate time of day. Hence there are no hour lines on the dial and the time of day is read only on the ellipse. As with most sundials, analemmatic sundials mark solar time rather than clock time.
Cranmer Park is a city park in Denver, United States located in the Hilltop neighborhood off Colorado Boulevard between East 1st and East 3rd Avenue. It is notable for its large sundial.
Man Enters the Cosmos is a cast bronze sculpture by Henry Moore located on the Lake Michigan lakefront outside the Adler Planetarium in the Museum Campus area of downtown Chicago, Illinois.
The Solarium Augusti or Horologium Augusti was a monument in the Campus Martius of ancient Rome constructed in 10 BCE under the Roman emperor Augustus. It included an Egyptian obelisk that had first been erected under the pharaoh Psamtik II used in some fashion as a gnomon. Once believed to have been a massive sundial, it is now more commonly understood to have been used with a meridian line used to track the solar year. It served as a monument of Augustus having brought Egypt under Roman rule and was also connected with the Altar of Augustan Peace commemorating the Pax Romana established by his ending the numerous civil wars that ended the Roman Republic. The Solarium was destroyed at some point during the Middle Ages. Its recovered obelisk is now known as the Obelisk of Montecitorio.
The ancient Egyptians were one of the first cultures to widely divide days into generally agreed-upon equal parts, using early timekeeping devices such as sundials, shadow clocks, and merkhets . Obelisks were also used by reading the shadow that they make. The clock was split into daytime and nighttime, and then into smaller hours.
The Carefree Sundial, in Carefree, Arizona, was designed by architect Joe Wong and solar engineer John I. Yellott (1908–1986), was erected in the Sundial Circle plaza in 1959. The sundial is made from a steel frame and covered in anodized copper. As originally designed the 1200mm wide gnomon acted as a heat collecting plate for a local heating scheme. It measures 90 feet (27 m) in diameter. The metal gnomon, the shadow-casting portion of the dial, stands 35 feet (11 m) above the plaza and extends 62 feet (19 m). Local apparent time is 27.7 minutes behind the meridian time which here is Mountain Standard Time. The hour markers are adjusted accordingly.
A sundial is a device that indicates time by using a light spot or shadow cast by the position of the Sun on a reference scale. As the Earth turns on its polar axis, the sun appears to cross the sky from east to west, rising at sun-rise from beneath the horizon to a zenith at mid-day and falling again behind the horizon at sunset. Both the azimuth (direction) and the altitude (height) can be used to create time measuring devices. Sundials have been invented independently in every major culture and became more accurate and sophisticated as the culture developed.
Gnomon Island is a small rocky island lying just north of Point Wild, on Elephant Island in the South Shetland Islands. It was charted by Ernest Shackleton's Endurance expedition, 1914–1916, and so named by them because when viewed from Point Wild the shape of the feature is suggestive of a gnomon, the elevated arm of a sundial.
Sundial, Boy With Spider is an outdoor sculpture and functional sundial by American artist Willard Dryden Paddock (1873–1956). It is located within the Oldfields estate on the grounds of the Indianapolis Museum of Art (IMA), in Indianapolis, Indiana, United States. The bronze sculpture, cast by the Gorham Manufacturing Company, depicts a boy sitting cross-legged with an open scroll in his lap.
A tide dial, also known as a mass dial or a scratch dial, is a sundial marked with the canonical hours rather than or in addition to the standard hours of daylight. Such sundials were particularly common between the 7th and 14th centuries in Europe, at which point they began to be replaced by mechanical clocks. There are more than 3,000 surviving tide dials in England and at least 1,500 in France.
Jantar Mantar is an Indian equinoctial sundial, consisting a gigantic triangular gnomon with the hypotenuse parallel to the Earth's axis.
A schema for horizontal dials is a set of instructions used to construct horizontal sundials using compass and straightedge construction techniques, which were widely used in Europe from the late fifteenth century to the late nineteenth century. The common horizontal sundial is a geometric projection of an equatorial sundial onto a horizontal plane.
The theorem of the gnomon states that certain parallelograms occurring in a gnomon have areas of equal size.
The Class of 1885 Memorial Sundial is a landmark at Columbia University, located at the center of the College Walk at the other end of Butler Plaza from Butler Library. Designed by astronomy professor Harold Jacoby in conjunction with McKim, Mead & White, it was completed in 1914. The 16-short-ton (15 t) granite sphere that once sat on top of it, at some point considered the largest stone sphere in the world, was removed in 1946 after it began to crack; efforts have been made toward its recovery since it was rediscovered in Michigan in 2001. The sundial's bare platform now serves as a popular meeting area for students, as well as a center for campus politics.
