Navigation[1] is a field of study that focuses on the process of monitoring and controlling the movement of a craft or vehicle from one place to another.[2] The field of navigation includes four general categories: land navigation,[3] marine navigation, aeronautic navigation, and space navigation.[1]
It is also the term of art used for the specialized knowledge used by navigators to perform navigation tasks. All navigational techniques involve locating the navigator's position compared to known locations or patterns.
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Navigation, in a broader sense, can refer to any skill or study that involves the determination of position and direction.[1] In this sense, navigation includes orienteering and pedestrian navigation.[1]
In the European medieval period, navigation was considered part of the set of seven mechanical arts, none of which were used for long voyages across open ocean. Polynesian navigation is probably the earliest form of open-ocean navigation; it was based on memory and observation recorded on scientific instruments like the Marshall Islands Stick Charts of Ocean Swells. Early Pacific Polynesians used the motion of stars, weather, the position of certain wildlife species, or the size of waves to find the path from one island to another.[citation needed]Maritime navigation using scientific instruments such as the mariner's astrolabe first occurred in the Mediterranean during the Middle Ages. Although land astrolabes were invented in the Hellenistic period and existed in classical antiquity and the Islamic Golden Age, the oldest record of a sea astrolabe is that of Spanish astronomer Ramon Llull dating from 1295.[4] The perfecting of this navigation instrument is attributed to Portuguese navigators during early Portuguese discoveries in the Age of Discovery.[5][6] The earliest known description of how to make and use a sea astrolabe comes from Spanish cosmographer Martn Corts de Albacar's Arte de Navegar (The Art of Navigation) published in 1551,[7] based on the principle of the archipendulum used in constructing the Egyptian pyramids.
Open-seas navigation using the astrolabe and the compass started during the Age of Discovery in the 15th century. The Portuguese began systematically exploring the Atlantic coast of Africa from 1418, under the sponsorship of Prince Henry. In 1488 Bartolomeu Dias reached the Indian Ocean by this route. In 1492 the Spanish monarchs funded Christopher Columbus's expedition to sail west to reach the Indies by crossing the Atlantic, which resulted in the Discovery of the Americas. In 1498, a Portuguese expedition commanded by Vasco da Gama reached India by sailing around Africa, opening up direct trade with Asia. Soon, the Portuguese sailed further eastward, to the Spice Islands in 1512, landing in China one year later.
The first circumnavigation of the earth was completed in 1522 with the Magellan-Elcano expedition, a Spanish voyage of discovery led by Portuguese explorer Ferdinand Magellan and completed by Spanish navigator Juan Sebastin Elcano after the former's death in the Philippines in 1521. The fleet of seven ships sailed from Sanlcar de Barrameda in Southern Spain in 1519, crossed the Atlantic Ocean and after several stopovers rounded the southern tip of South America. Some ships were lost, but the remaining fleet continued across the Pacific making a number of discoveries including Guam and the Philippines. By then, only two galleons were left from the original seven. The Victoria led by Elcano sailed across the Indian Ocean and north along the coast of Africa, to finally arrive in Spain in 1522, three years after its departure. The Trinidad sailed east from the Philippines, trying to find a maritime path back to the Americas, but was unsuccessful. The eastward route across the Pacific, also known as the tornaviaje (return trip) was only discovered forty years later, when Spanish cosmographer Andrs de Urdaneta sailed from the Philippines, north to parallel 39, and hit the eastward Kuroshio Current which took its galleon across the Pacific. He arrived in Acapulco on October 8, 1565.
Roughly, the latitude of a place on Earth is its angular distance north or south of the equator.[9] Latitude is usually expressed in degrees (marked with ) ranging from 0 at the Equator to 90 at the North and South poles.[9] The latitude of the North Pole is 90 N, and the latitude of the South Pole is 90 S.[9] Mariners calculated latitude in the Northern Hemisphere by sighting the pole star (Polaris) with a sextant and using sight reduction tables to correct for height of eye and atmospheric refraction. The height of Polaris in degrees above the horizon is the latitude of the observer, within a degree or so.
Similar to latitude, the longitude of a place on Earth is the angular distance east or west of the prime meridian or Greenwich meridian.[9] Longitude is usually expressed in degrees (marked with ) ranging from 0 at the Greenwich meridian to 180 east and west. Sydney, for example, has a longitude of about 151 east. New York City has a longitude of 74 west. For most of history, mariners struggled to determine longitude. Longitude can be calculated if the precise time of a sighting is known. Lacking that, one can use a sextant to take a lunar distance (also called the lunar observation, or "lunar" for short) that, with a nautical almanac, can be used to calculate the time at zero longitude (see Greenwich Mean Time).[10] Reliable marine chronometers were unavailable until the late 18th century and not affordable until the 19th century.[11][12][13] For about a hundred years, from about 1767 until about 1850,[14] mariners lacking a chronometer used the method of lunar distances to determine Greenwich time to find their longitude. A mariner with a chronometer could check its reading using a lunar determination of Greenwich time.[11][15]
In navigation, a rhumb line (or loxodrome) is a line crossing all meridians of longitude at the same angle, i.e. a path derived from a defined initial bearing. That is, upon taking an initial bearing, one proceeds along the same bearing, without changing the direction as measured relative to true or magnetic north.
Most modern navigation relies primarily on positions determined electronically by receivers collecting information from satellites. Most other modern techniques rely on finding intersecting lines of position or LOP.[16]
A line of position can refer to two different things, either a line on a chart or a line between the observer and an object in real life.[17] A bearing is a measure of the direction to an object.[17] If the navigator measures the direction in real life, the angle can then be drawn on a nautical chart and the navigator will be somewhere on that bearing line on the chart.[17]
In addition to bearings, navigators also often measure distances to objects.[16] On the chart, a distance produces a circle or arc of position.[16] Circles, arcs, and hyperbolae of positions are often referred to as lines of position.
Methods of navigation have changed through history.[20] Each new method has enhanced the mariner's ability to complete his voyage.[20] One of the most important judgments the navigator must make is the best method to use.[20] Some types of navigation are depicted in the table.
Piloting (also called pilotage) involves navigating an aircraft by visual reference to landmarks,[22] or a water vessel in restricted waters and fixing its position as precisely as possible at frequent intervals.[23] More so than in other phases of navigation, proper preparation and attention to detail are important.[23] Procedures vary from vessel to vessel, and between military, commercial, and private vessels.[23] As pilotage takes place in shallow waters, it typically involves following courses to ensure sufficient under keel clearance, ensuring a sufficient depth of water below the hull as well as a consideration for squat.[24] It may also involve navigating a ship within a river, canal or channel in close proximity to land.[24]
A military navigation team will nearly always consist of several people.[23] A military navigator might have bearing takers stationed at the gyro repeaters on the bridge wings for taking simultaneous bearings, while the civilian navigator on a merchant ship or leisure craft must often take and plot their position themselves, typically with the aid of electronic position fixing.[23] While the military navigator will have a bearing book and someone to record entries for each fix, the civilian navigator will simply pilot the bearings on the chart as they are taken and not record them at all.[23] If the ship is equipped with an ECDIS, it is reasonable for the navigator to simply monitor the progress of the ship along the chosen track, visually ensuring that the ship is proceeding as desired, checking the compass, sounder and other indicators only occasionally.[23] If a pilot is aboard, as is often the case in the most restricted of waters, his judgement can generally be relied upon, further easing the workload.[23] But should the ECDIS fail, the navigator will have to rely on his skill in the manual and time-tested procedures.[23]
Celestial navigation systems are based on observation of the positions of the Sun, Moon, planets and navigational stars. Such systems are in use as well for terrestrial navigating as for interstellar navigating. By knowing which point on the rotating Earth a celestial object is above and measuring its height above the observer's horizon, the navigator can determine his distance from that subpoint. A nautical almanac and a marine chronometer are used to compute the subpoint on Earth a celestial body is over, and a sextant is used to measure the body's angular height above the horizon. That height can then be used to compute distance from the subpoint to create a circular line of position. A navigator shoots a number of stars in succession to give a series of overlapping lines of position. Where they intersect is the celestial fix. The Moon and Sun may also be used. The Sun can also be used by itself to shoot a succession of lines of position (best done around local noon) to determine a position.[25] 152ee80cbc
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