French Geodesic Mission to the EquatorThe French Geodesic Mission to the Equator (Expédition géodésique française en Équateur), also called the French Geodesic Mission to Peru and the Spanish-French Geodesic Mission, was an 18th-century expedition to what is now Ecuador carried out for the purpose of performing an arc measurement, measuring the length of a degree of latitude near the Equator, by which the Earth radius can be inferred. The mission was one of the first geodesic (or geodetic) missions carried out under modern scientific principles, and the first major international scientific expedition.
History of geodesyThe history of geodesy deals with the historical development of measurements and representations of the Earth. The corresponding scientific discipline, geodesy (/dʒiːˈɒdɪsi/), began in pre-scientific antiquity and blossomed during the Age of Enlightenment. Early ideas about the figure of the Earth held the Earth to be flat (see flat Earth) and the heavens a physical dome spanning over it. Two early arguments for a spherical Earth were that lunar eclipses were seen as circular shadows and that Polaris is seen lower in the sky as one travels South.
Figure of the EarthFigure of the Earth is a term of art in geodesy that refers to the size and shape used to model Earth. The size and shape it refers to depend on context, including the precision needed for the model. A sphere is a well-known historical approximation of the figure of the Earth that is satisfactory for many purposes. Several models with greater accuracy (including ellipsoid) have been developed so that coordinate systems can serve the precise needs of navigation, surveying, cadastre, land use, and various other concerns.
Earth's rotationEarth's rotation or Earth's spin is the rotation of planet Earth around its own axis, as well as changes in the orientation of the rotation axis in space. Earth rotates eastward, in prograde motion. As viewed from the northern polar star Polaris, Earth turns counterclockwise. The North Pole, also known as the Geographic North Pole or Terrestrial North Pole, is the point in the Northern Hemisphere where Earth's axis of rotation meets its surface. This point is distinct from Earth's North Magnetic Pole.
Earth radiusEarth radius (denoted as R🜨 or ) 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 (equatorial radius, denoted a) to a minimum of nearly (polar radius, denoted b). A nominal Earth radius is sometimes used as a unit of measurement in astronomy and geophysics, which is recommended by the International Astronomical Union to be the equatorial value. A globally-average value is usually considered to be with a 0.
Nautical mileA 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. Today the international nautical mile is defined as . The derived unit of speed is the knot, one nautical mile per hour. There is no single internationally agreed symbol, with several symbols in use. NM is used by the International Civil Aviation Organization.
Degree (angle)A degree (in full, a degree of arc, arc degree, or arcdegree), usually denoted by ° (the degree symbol), is a measurement of a plane angle in which one full rotation is 360 degrees. It is not an SI unit—the SI unit of angular measure is the radian—but it is mentioned in the SI brochure as an accepted unit. Because a full rotation equals 2pi radians, one degree is equivalent to pi/180 radians. The original motivation for choosing the degree as a unit of rotations and angles is unknown.
Paris meridianThe Paris meridian is a meridian line running through the Paris Observatory in Paris, France – now longitude 2°20′14.02500′′ East. It was a long-standing rival to the Greenwich meridian as the prime meridian of the world. The "Paris meridian arc" or "French meridian arc" (French: la Méridienne de France) is the name of the meridian arc measured along the Paris meridian. The French meridian arc was important for French cartography, inasmuch as the triangulations of France began with the measurement of the French meridian arc.
François AragoDominique François Jean Arago (Domènec Francesc Joan Aragó), known simply as François Arago (fʁɑ̃swa aʁaɡo; Catalan: Francesc Aragó, fɾənˈsɛsk əɾəˈɣo; 26 February 1786 - 2 October 1853), was a French mathematician, physicist, astronomer, freemason, supporter of the Carbonari revolutionaries and politician. Arago was born at Estagel, a small village of 3,000 near Perpignan, in the département of Pyrénées-Orientales, France, where his father held the position of Treasurer of the Mint.
Geodesics on an ellipsoidThe study of geodesics on an ellipsoid arose in connection with geodesy specifically with the solution of triangulation networks. The figure of the Earth is well approximated by an oblate ellipsoid, a slightly flattened sphere. A geodesic is the shortest path between two points on a curved surface, analogous to a straight line on a plane surface. The solution of a triangulation network on an ellipsoid is therefore a set of exercises in spheroidal trigonometry .
