In geodesy and navigation, a meridian arc is the curve between two points near the Earth's surface having the same longitude. The term may refer either to a segment of the meridian, or to its length. Both the practical determination of meridian arcs (employing measuring instruments in field campaigns) as well as its theoretical calculation (based on geometry and abstract mathematics) have been pursued for many years.
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Meridian arc in the context of Nautical mile
A nautical mile is a unit of length used in air, marine, and space navigation, and for the definition of territorial waters. Historically, it was defined as the meridian arc length corresponding to one minute (1/60 of a degree) of latitude at the equator, so that Earth's polar circumference is very near to 21,600 nautical miles (that is 60 minutes × 360 degrees). Today the international nautical mile is defined as exactly 1,852 metres (about 6,076 ft; 1.151 mi). The derived unit of speed is the knot, one nautical mile per hour.
The nautical mile is not part of the International System of Units (SI), nor is it accepted for use with SI. However, it is still in common use globally in air, marine, and space contexts due to its correspondence with geographic coordinates.
Meridian arc in the context of George Everest
Sir George Everest, CB, FRS, FRAS, FRGS (/ˈiːvrɪst/, EEV-rist; 4 July 1790 – 1 December 1866) was a British surveyor and geographer who served as Surveyor General of India from 1830 to 1843.
After a military education, Everest joined the East India Company and arrived in India at the age of 16. He was eventually made an assistant to William Lambton on the Great Trigonometric Survey, and replaced Lambton as superintendent of the survey in 1823. Everest was largely responsible for surveying the meridian arc from the southernmost point of India north to Nepal, a distance of about 2,400 kilometres (1,500 mi), a task that took from 1806 to 1841 to complete. He was made Surveyor General of India in 1830, retiring in 1843 and returning to England.
Meridian arc in the context of Minute of arc
A minute of arc, arcminute (abbreviated as arcmin), arc minute, or minute arc, denoted by the symbol ′, is a unit of angular measurement equal to 1/60 of a degree. Since one degree is 1/360 of a turn, or complete rotation, one arcminute is 1/21600 of a turn. The nautical mile (nmi) was originally defined as the arc length of a minute of latitude on a spherical Earth, so the actual Earth's circumference is very near 21600 nmi. A minute of arc is π/10800 of a radian.
A second of arc, arcsecond (abbreviated as arcsec), or arc second, denoted by the symbol ″, is a unit of angular measurement equal to 1/60 of a minute of arc, 1/3600 of a degree, 1/1296000 of a turn, and π/648000 (about 1/206264.8) of a radian.
Meridian arc in the context of Arc measurement
Arc measurement, sometimes called degree measurement (German: Gradmessung), is the astrogeodetic technique of determining the radius of Earth and, by extension, its circumference. More specifically, it seeks to determine the local Earth radius of curvature of the figure of the Earth, by relating the latitude difference (sometimes also the longitude difference) and the geographic distance (arc length) surveyed between two locations on Earth's surface. The most common variant involves only astronomical latitudes and the meridian arc length and is called meridian arc measurement; other variants may involve only astronomical longitude (parallel arc measurement) or both geographic coordinates (oblique arc measurement).Arc measurement campaigns in Europe were the precursors to the International Association of Geodesy (IAG).Nowadays, the method is replaced by worldwide geodetic networks and by satellite geodesy.