A nocturnal is an instrument used to determine the local time based on the relative

position Position often refers to: * Position (geometry), the spatial location (rather than orientation) of an entity * Position, a job or occupation Position may also refer to: Games and recreation * Position (poker), location relative to the dealer * ...

s of two or more

star A star is an astronomical object comprising a luminous spheroid of plasma (physics), plasma held together by its gravity. The List of nearest stars and brown dwarfs, nearest star to Earth is the Sun. Many other stars are visible to the naked ...

s in the

night sky The night sky is the nighttime appearance of celestial objects like stars, planets, and the Moon, which are visible in a clear sky between sunset and sunrise, when the Sun is below the horizon. Natural light sources in a night sky include ...

. Sometimes called a ''horologium nocturnum'' (time instrument for night) or ''nocturlabe'' (in French and occasionally used by English writers), it is related to the

astrolabe An astrolabe ( grc, ἀστρολάβος ; ar, ٱلأَسْطُرلاب ; persian, ستاره‌یاب ) is an ancient astronomical instrument that was a handheld model of the universe. Its various functions also make it an elaborate inclin ...

and

sundial A sundial is a horological device that tells the time of day (referred to as civil time in modern usage) 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 ...

. Knowing the time is important in

piloting Piloting or pilotage is the process of navigating on water or in the air using fixed points of reference on the sea or on land, usually with reference to a nautical chart or aeronautical chart to obtain a fix of the position of the vessel or air ...

for calculating

tide Tides are the rise and fall of sea levels caused by the combined effects of the gravity, gravitational forces exerted by the Moon (and to a much lesser extent, the Sun) and are also caused by the Earth and Moon orbiting one another. Tide t ...

s and some nocturnals incorporate tide charts for important ports. Even if the nightly course of the stars has been known since antiquity, mentions of a dedicated instrument for its measurement are not found before the Middle Ages. The earliest image presenting the use of a nocturnal is in a manuscript dated from the 12th century.Farre i Olive E., (1996): ''La Sphaera Horarum Noctis de Ramon Llull'', "La Busca de Paper" n. 22, Primavera, p. 3-12 (edicion bilingue)

Raymond Lull Ramon Llull (; c. 1232 – c. 1315/16) was a philosopher, theologian, poet, missionary, and Christian apologist from the Kingdom of Majorca. He invented a philosophical system known as the ''Art'', conceived as a type of universal logic to pro ...

repeatedly described the use of a ''sphaera horarum noctis'' or ''astrolabium nocturnum''.Raimon Lull, ''Liber Principorum medicinae'' in ''Opera omnia'', vol.1, Chap. 36, par.30, Mainz, 1721; Earlier Lull mentions the nocturnal in his ''Nova geometria'' (1299). With

Martín Cortés de Albacar Martín Cortés de Albacar (1510–1582) was a Spanish cosmographer.p131 Antonio Barrera-Osorio ''Experiencing nature: the Spanish American empire and the early scientific revolution;'' University of Texas Press, 2006 In 1551 he published the st ...

's book ''Arte de Navegar'', published in 1551 the name and the instrument gained a larger popularity.Harriet Wynter and Anthony Turner, ''Scientific Instruments'', Studio Vista, 1975, It was described also c. 1530 by

Petrus Apianus Petrus Apianus (April 16, 1495 – April 21, 1552), also known as Peter Apian, Peter Bennewitz, and Peter Bienewitz, was a German humanist, known for his works in mathematics, astronomy and cartography. His work on "cosmography", the field that de ...

in his ''Cosmographicus Liber'', republished later by

Gemma Frisius Gemma Frisius (; born Jemme Reinerszoon; December 9, 1508 – May 25, 1555) was a Frisian physician, mathematician, cartographer, philosopher, and instrument maker. He created important globes, improved the mathematical instruments of his d ...

with a widely circulated illustration of the instrument while being used by an observer.

Construction

Nocturnals have been most commonly constructed of

wood Wood is a porous and fibrous structural tissue found in the stems and roots of trees and other woody plants. It is an organic materiala natural composite of cellulose fibers that are strong in tension and embedded in a matrix of lignin th ...

brass Brass is an alloy of copper (Cu) and zinc (Zn), in proportions which can be varied to achieve different mechanical, electrical, and chemical properties. It is a substitutional alloy: atoms of the two constituents may replace each other with ...

. A nocturnal will have an outer disc marked with the months of the year, and an inner disc marked with hours (and perhaps half hours, or quarter hours on the largest instruments) as well as locations for one or more reference stars. It will also have a pointer rotating on the same axis as the discs, sometimes extended beyond the rim. The axis, or pivot point, must be such that a star can be sighted through it; usually a hollow rivet is used. Since the instrument is used at night, markings may be exaggerated or raised. Often the inner disc has a diagram of the necessary constellations and stars, to aid in locating them.

Usage

A nocturnal is a simple

analog computer An analog computer or analogue computer is a type of computer that uses the continuous variation aspect of physical phenomena such as electrical, mechanical, or hydraulic quantities (''analog signals'') to model the problem being solved. In c ...

, made of two or more dials, that will provide the local time based on the time of year and a sighting of

Polaris Polaris is a star in the northern circumpolar constellation of Ursa Minor. It is designated α Ursae Minoris ( Latinized to ''Alpha Ursae Minoris'') and is commonly called the North Star or Pole Star. With an apparent magnitude that ...

, the North Star, and one or more other stars. In the

northern hemisphere The Northern Hemisphere is the half of Earth that is north of the Equator. For other planets in the Solar System, north is defined as being in the same celestial hemisphere relative to the invariable plane of the solar system as Earth's Nort ...

, all stars will appear to rotate about the North Star during the night, and their positions, like the progress of the

sun The Sun is the star at the center of the Solar System. It is a nearly perfect ball of hot plasma, heated to incandescence by nuclear fusion reactions in its core. The Sun radiates this energy mainly as light, ultraviolet, and infrared radi ...

, can be used to determine the time. The positions of the stars will change based on the time of year. The most commonly used reference stars are the pointer stars from the

Big Dipper The Big Dipper ( US, Canada) or the Plough ( UK, Ireland) is a large asterism consisting of seven bright stars of the constellation Ursa Major; six of them are of second magnitude and one, Megrez (δ), of third magnitude. Four define a "bowl" ...

(

Ursa Major Ursa Major (; also known as the Great Bear) is a constellation in the northern sky, whose associated mythology likely dates back into prehistory. Its Latin name means "greater (or larger) bear," referring to and contrasting it with nearby Ursa ...

) or

Kochab Beta Ursae Minoris (β Ursae Minoris, abbreviated β UMi, Beta UMi), formally named Kochab , is the brightest star in the bowl of the Little Dipper asterism (which is part of the constellation of Ursa Minor), and only slightly fainter tha ...

from the

Little Dipper Little is a synonym for small size and may refer to: Arts and entertainment * ''Little'' (album), 1990 debut album of Vic Chesnutt * ''Little'' (film), 2019 American comedy film *The Littles, a series of children's novels by American author John P ...

(Ursa Minor). The star Schedar in Cassiopeia may also be used, since it is on the opposite side of the sky from Ursa Major. The inner disc is rotated so that the mark for the chosen reference star points to the current date on the outer disc. The north star is sighted through the center of the device, and the pointer arm is rotated to point at the chosen reference star. The intersection of the pointer arm with the hour markings on the inner disc indicates the time. The instrument must be held upright, and should have a handle or similar hint as to which direction is down. It is not possible to convert the local time to a standard time such as UTC without accurate knowledge of the observer's

longitude Longitude (, ) is a geographic coordinate that specifies the east–west position of a point on the surface of the Earth, or another celestial body. It is an angular measurement, usually expressed in degrees and denoted by the Greek letter l ...

. Similarly, it is not possible to determine longitude unless the observer also knows the standard time from a

chronometer A clock or a timepiece is a device used to measure and indicate time. The clock is one of the oldest human inventions, meeting the need to measure intervals of time shorter than the natural units such as the day, the lunar month and th ...

References

External links

British Museum
– Nocturnal from an astrological compendium
Simulation
– Video and description, also, many devices
A working nocturnal in coin form
{{DEFAULTSORT:Nocturnal (Instrument) Navigational equipment Astronomical instruments Historical scientific instruments

Construction

Usage

See also

References

External links