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Sextant
A sextant is a doubly reflecting navigation instrument that measures the angular distance between two visible objects. The primary use of a sextant is to measure the angle between an astronomical object and the horizon for the purposes of celestial navigation. The estimation of this angle, the altitude, is known as ''sighting'' or ''shooting'' the object, or ''taking a sight''. The angle, and the time when it was measured, can be used to calculate a position line on a nautical or aeronautical chart—for example, sighting the Sun at noon or Polaris at night (in the Northern Hemisphere) to estimate latitude (with sight reduction). Sighting the height of a landmark can give a measure of ''distance off'' and, held horizontally, a sextant can measure angles between objects for a position on a chart. A sextant can also be used to measure the lunar distance between the moon and another celestial object (such as a star or planet) in order to determine Greenwich Mean Time and hence ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Reflecting Instrument
Reflecting instruments are those that use mirrors to enhance their ability to make measurements. In particular, the use of mirrors permits one to observe two objects simultaneously while measuring the angular distance between the objects. While reflecting instruments are used in many professions, they are primarily associated with celestial navigation as the need to solve navigation problems, in particular the problem of the longitude, was the primary motivation in their development. Objectives of the instruments The purpose of reflecting instruments is to allow an observer to measure the altitude of a celestial object or the angular distance between two objects. The driving force behind the developments discussed here was the solution to the problem of finding one's longitude at sea. The solution to this problem was seen to require an accurate means of measuring angles and the accuracy was seen to rely on the observer's ability to measure this angle by simultaneously observing ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Celestial Navigation
Celestial navigation, also known as astronavigation, is the practice of position fixing using stars and other celestial bodies that enables a navigator to accurately determine their actual current physical position in space or on the surface of the Earth without relying solely on estimated positional calculations, commonly known as dead reckoning. Celestial navigation is performed without using satellite navigation or other similar modern electronic or digital positioning means. Celestial navigation uses "sights," or timed angular measurements, taken typically between a celestial body (e.g., the Sun, the Moon, a planet, or a star) and the visible horizon. Celestial navigation can also take advantage of measurements between celestial bodies without reference to the Earth's horizon, such as when the Moon and other selected bodies are used in the practice called "lunars" or the Lunar distance (navigation), lunar distance method, used for determining precise time when time is u ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Octant (instrument)
The octant, also called a reflecting quadrant (instrument), quadrant, is a reflecting instrument used in navigation. Etymology The name ''octant'' derives from the Latin ''octans'' meaning ''eighth part of a circle'', because the instrument's arc is Circular sector, one eighth of a circle. ''Reflecting quadrant'' derives from the instrument using mirrors to reflect the path of light to the observer and, in doing so, doubles the angle measured. This allows the instrument to use a one-eighth of a Turn (geometry), turn to measure a quarter-Turn (geometry), turn or Circular sector, quadrant. Origin of the octant Newton's reflecting quadrant Isaac Newton's reflecting quadrant was invented around 1699. A detailed description of the instrument was given to Edmond Halley, but the description was not published until after Halley's death in 1742. It is not known why Halley did not publish the information during his life, as this prevented Newton from getting the credit for the inven ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Quadrant (instrument)
A quadrant is an instrument used to measure angles up to 90°. Different versions of this instrument could be used to calculate various readings, such as longitude, latitude, and time of day. It was first proposed by Ptolemy as a better kind of astrolabe. Several different variations of the instrument were later produced by medieval Muslim astronomers. Mural quadrants were important astronomical instruments in 18th-century European observatories, establishing a use for positional astronomy. Etymology The term ''quadrant'', meaning one fourth, refers to the fact that early versions of the instrument were derived from astrolabes. The quadrant condensed the workings of the astrolabe into an area one fourth the size of the astrolabe face; it was essentially a quarter of an astrolabe. History During Rigvedic times in ancient India, quadrants called 'Tureeyam's were used to measure the extent of a great solar eclipse. The use of a Tureeyam for observing a solar eclipse by Ri ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Lunar Distance (navigation)
In celestial navigation, lunar distance, also called a ''lunar'', is the angular distance between the Moon and another celestial body. The lunar distances method uses this angle and a nautical almanac to calculate Greenwich time if so desired, or by extension any other time. That calculated time can be used in solving a spherical triangle. The theory was first published by Johannes Werner in 1524, before the necessary almanacs had been published. A fuller method was published in 1763 and used until about 1850 when it was superseded by the marine chronometer. A similar method uses the positions of the Galilean moons of Jupiter. Purpose In celestial navigation, knowledge of the time at Greenwich (or another known place) and the measured positions of one or more celestial objects allows the navigator to calculate longitude. Reliable marine chronometers were unavailable until the late 18th century and not affordable until the 19th century. After the method was firs ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Sight Reduction
In astronavigation, sight reduction is the process of deriving from a Sight (device), sight (in celestial navigation usually obtained using a sextant) the information needed for establishing a line of position, generally by intercept method. Sight is defined as the observation of the altitude, and sometimes also the azimuth, of a celestial body for a line of position; or the data obtained by such observation. The mathematical basis of sight reduction is the circle of equal altitude. The calculation can be done by computer, or by hand via tabular methods and longhand methods. Algorithm Given: * Lat, the latitude (North - positive, South - negative), Lon the longitude (East - positive, West - negative), both approximate (assumed); * Dec, the declination of the body observed; * GHA, the Greenwich hour angle of the body observed; * LHA = GHA + Lon, the local hour angle of the body observed. First calculate the altitude of the celestial body Hc using the equation of circle of equal ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Carlos Viegas Gago Coutinho
Carlos Viegas Gago Coutinho, GCTE, GCC (; 17 February 1869 – 18 February 1959), generally known simply as Gago Coutinho, was a Portuguese geographer, cartographer, naval officer, historian and aviator. An aviation pioneer, Gago Coutinho and Sacadura Cabral were the first to cross the South Atlantic Ocean by air, in a journey from March to June 1922, started in Lisbon, Portugal, and finished in Rio de Janeiro, Brazil, using a seaplane variant of the British reconnaissance biplane Fairey III. In June 2022, the centenary of the first aerial crossing of the South Atlantic, it was announced that Faro Airport would officially change its name to Gago Coutinho Airport. Early life He was born in Belém, Lisbon, in a modest family, the son of José Viegas Gago Coutinho and his cousin, Fortunata Maria Coutinho. He finished high school in 1885, and entered the Polytechnic School, where he studied for one year, as preparation for his entrance at the Naval School, in Alfeite, Almada, ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
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 lambda (λ). Meridians are imaginary semicircular lines running from pole to pole that connect points with the same longitude. The prime meridian defines 0° longitude; by convention the International Reference Meridian for the Earth passes near the Royal Observatory in Greenwich, south-east London on the island of Great Britain. Positive longitudes are east of the prime meridian, and negative ones are west. Because of the Earth's rotation, there is a close connection between longitude and time measurement. Scientifically precise local time varies with longitude: a difference of 15° longitude corresponds to a one-hour difference in local time, due to the differing position in relation to the Sun. Comparing local time to an absol ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Backstaff
The backstaff is a celestial navigation, navigational instrument that was used to measure the Horizontal coordinate system#Altitude, altitude of a astronomical object, celestial body, in particular the Sun or Moon. When observing the Sun, users kept the Sun to their back (hence the name) and observed the shadow cast by the upper vane on a horizon vane. It was invented by the English navigator John Davis (English explorer), John Davis, who described it in his book ''Seaman's Secrets'' in 1594. Types of backstaffs Backstaff is the name given to any instrument that measures the altitude of the sun by the projection of a shadow. It appears that the idea for measuring the sun's altitude using back observations originated with Thomas Harriot. Many types of instruments evolved from the cross-staff that can be classified as backstaffs. Only the Davis quadrant remains dominant in the history of navigation instruments. Indeed, the Davis quadrant is essentially synonymous with backstaff. ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Alidade
An alidade () (archaic forms include alhidade, alhidad, alidad) or a turning board is a device that allows one to sight a distant object and use the line of sight to perform a task. This task can be, for example, to Triangulation (surveying), triangulate a scale map on site using a plane table drawing of intersecting lines in the direction of the object from two or more points or to measure the angle and horizontal distance to the object from some reference point's Polar coordinate system, polar measurement. Angles measured can be horizontal, vertical or in any chosen plane. The alidade sighting ruler was originally a part of many types of scientific and astronomical instrument. At one time, some alidades, particularly using Graduation (instrument), circular graduations as on astrolabes, were also called ''diopters''. With modern technology, the name is applied to complete instruments such as the 'plane table alidade'. Origins The word in Arabic (, , ), signifies the same de ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Circular Sector
A circular sector, also known as circle sector or disk sector or simply a sector (symbol: ⌔), is the portion of a disk (a closed region bounded by a circle) enclosed by two radii and an arc, with the smaller area being known as the ''minor sector'' and the larger being the ''major sector''. In the diagram, is the central angle, the radius of the circle, and is the arc length of the minor sector. The angle formed by connecting the endpoints of the arc to any point on the circumference that is not in the sector is equal to half the central angle. Types A sector with the central angle of 180° is called a '' half-disk'' and is bounded by a diameter and a semicircle. Sectors with other central angles are sometimes given special names, such as quadrants (90°), sextants (60°), and octants (45°), which come from the sector being one quarter, sixth or eighth part of a full circle, respectively. Area The total area of a circle is . The area of the sector can be obtai ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
