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A minute of arc, arcminute (arcmin), arc minute, or minute arc, denoted by the symbol ′, is a unit of angular measurement equal to 1/60 of one 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 circumference is very near 21600 nmi. A minute of arc is π/10800 of a radian.
In astronomy, declination is one of the two angles that locate a point on the celestial sphere in the equatorial coordinate system, the other being hour angle. Declination's angle is measured north or south of the celestial equator, along the hour circle passing through the point in question.
Geodesy is the science of measuring and representing the geometry, gravity, and spatial orientation of the Earth in temporally varying 3D. It is called planetary geodesy when studying other astronomical bodies, such as planets or circumplanetary systems.
In geography, latitude is a coordinate that specifies the north–south position of a point on the surface of the Earth or another celestial body. Latitude is given as an angle that ranges from –90° at the south pole to 90° at the north pole, with 0° at the Equator. Lines of constant latitude, or parallels, run east–west as circles parallel to the equator. Latitude and longitude are used together as a coordinate pair to specify a location on the surface of the Earth.
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.
The mile, sometimes the international mile or statute mile to distinguish it from other miles, is a British imperial unit and United States customary unit of distance; both are based on the older English unit of length equal to 5,280 English feet, or 1,760 yards. The statute mile was standardised between the Commonwealth of Nations and the United States by an international agreement in 1959, when it was formally redefined with respect to SI units as exactly 1,609.344 metres.
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 of latitude at the equator. Today the international nautical mile is defined as 1,852 metres. The derived unit of speed is the knot, one nautical mile per hour.
The geographic coordinate system (GCS) is a spherical or geodetic coordinate system for measuring and communicating positions directly on the Earth as latitude and longitude. It is the simplest, oldest and most widely used of the various spatial reference systems that are in use, and forms the basis for most others. Although latitude and longitude form a coordinate tuple like a cartesian coordinate system, the geographic coordinate system is not cartesian because the measurements are angles and are not on a planar surface.
Earth radius is the distance from the center of Earth to a point on or near its surface. Approximating the figure of Earth by an Earth spheroid, the radius ranges from a maximum of nearly 6,378 km (3,963 mi) to a minimum of nearly 6,357 km (3,950 mi).
In geodesy, the figure of the Earth is the size and shape used to model planet Earth. The kind of figure depends on application, including the precision needed for the model. A spherical Earth is a well-known historical approximation that is satisfactory for geography, astronomy and many other purposes. Several models with greater accuracy have been developed so that coordinate systems can serve the precise needs of navigation, surveying, cadastre, land use, and various other concerns.
The Ordnance Survey National Grid reference system (OSGB) is a system of geographic grid references used in Great Britain, distinct from latitude and longitude.
A unit of length refers to any arbitrarily chosen and accepted reference standard for measurement of length. The most common units in modern use are the metric units, used in every country globally. In the United States the U.S. customary units are also in use. British Imperial units are still used for some purposes in the United Kingdom and some other countries. The metric system is sub-divided into SI and non-SI units.
The Geodetic Reference System 1980 is a geodetic reference system consisting of a global reference ellipsoid and a normal gravity model.
A league is a unit of length. It was common in Europe and Latin America, but is no longer an official unit in any nation. Derived from an ancient Celtic unit and adopted by the Romans as the leuga, the league became a common unit of measurement throughout western Europe. Since the Middle Ages, many values have been specified in several countries.
The scale of a map is the ratio of a distance on the map to the corresponding distance on the ground. This simple concept is complicated by the curvature of the Earth's surface, which forces scale to vary across a map. Because of this variation, the concept of scale becomes meaningful in two distinct ways.
In geodesy and navigation, a meridian arc is the curve between two points on the Earth's surface having the same longitude. The term may refer either to a segment of the meridian, or to its length.
An Earth ellipsoid or Earth spheroid is a mathematical figure approximating the Earth's form, used as a reference frame for computations in geodesy, astronomy, and the geosciences. Various different ellipsoids have been used as approximations.
The equator is a circle of latitude that divides a spheroid, such as Earth, into the northern and southern hemispheres. On Earth, it is an imaginary line located at 0 degrees latitude, about 40,075 km (24,901 mi) in circumference, halfway between the North and South poles. The term can also be used for any other celestial body that is roughly spherical.
In geodesy and geophysics, theoretical gravity or normal gravity is an approximation of the true gravity on Earth's surface by means of a mathematical model representing Earth. The most common model of a smoothed Earth is a rotating Earth ellipsoid of revolution.
Earth's circumference is the distance around Earth. Measured around the equator, it is 40,075.017 km (24,901.461 mi). Measured around the poles, the circumference is 40,007.863 km (24,859.734 mi).
References
- 1 2 Ministry of Defence Staff, Navy Dept, Great Britain Ministry of Defence (1987). Admiralty manual of navigation. H.M. Stationery Office. p. 7. ISBN 9780117728806.
{{cite book}}: CS1 maint: multiple names: authors list (link) - ↑ "Glossary of Marine Navigation", The American Practical Navigator, vol. II (2017 ed.), National Geospatial-Intelligence Agency, p. 346
- ↑ This is used by the international (ITRS) and American WGS 84) coordinate reference system for the world.
- ↑ Rabounski, Dmitri (2008). "Biography of Ole Rømer" (PDF). The Abraham Zelmanov Journal. 1: 2. Archived (PDF) from the original on 2011-07-15. Retrieved 1 February 2018.
- ↑ David Greenhood; Gerard L. Alexander (1964). Mapping . University of Chicago Press. pp. 51–52. ISBN 9780226306971.
- ↑ "NIST Handbook 44, Specifications, Tolerances, and Other Technical Requirements for Weighing and Measuring Devices, General Tables of Units of Measurement (PDF). NIST (Report). November 2014. p. C-15 (Appendix C, footnote 14). Archived (PDF) from the original on 2017-05-05. Retrieved April 9, 2019.
- ↑ "Units of Weight and Measure (United States Customary and Metric) Definition and Tables of Equivalents" (PDF). National Bureau of Standards (Report). July 1, 1955. p. 4. Archived (PDF) from the original on 2017-02-01. Retrieved May 5, 2021.
- ↑ Weast, Robert C. (ed.). CRC Handbook of Chemistry and Physics, 62nd edition, 1981-1982. Boca Raton, Florida: CRC Press. p. F-297. ISBN 978-0849304620.
- ↑ "Journal of Continental Congress, Vol. 27". A Century of Lawmaking for a New Nation: U.S. Congressional Documents and Debates, 1774 - 1875. May 28, 1784. p. 446. Retrieved April 9, 2019– via Library of congress.