History of the metreThe history of the metre starts with the Scientific Revolution that is considered to have begun with Nicolaus Copernicus's publication of De revolutionibus orbium coelestium in 1543. Increasingly accurate measurements were required, and scientists looked for measures that were universal and could be based on natural phenomena rather than royal decree or physical prototypes. Rather than the various complex systems of subdivision then in use, they also preferred a decimal system to ease their calculations.
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.
Meridian arcIn 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. The purpose of measuring meridian arcs is to determine a figure of the Earth. One or more measurements of meridian arcs can be used to infer the shape of the reference ellipsoid that best approximates the geoid in the region of the measurements.
Giovanni Domenico CassiniGiovanni Domenico Cassini, also known as Jean-Dominique Cassini (8 June 1625 – 14 September 1712) was an Italian (naturalised French) mathematician, astronomer and engineer. Cassini was born in Perinaldo, near Imperia, at that time in the County of Nice, part of the Savoyard state. Cassini is known for his work on astronomy and engineering. He discovered four satellites of the planet Saturn and noted the division of the rings of Saturn; the Cassini Division was named after him.
Arc measurementArc measurement, sometimes degree measurement (Gradmessung), is the astrogeodetic technique of determining of the radius of Earth – more specifically, 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.
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.
MetrologyMetrology is the scientific study of measurement. It establishes a common understanding of units, crucial in linking human activities. Modern metrology has its roots in the French Revolution's political motivation to standardise units in France when a length standard taken from a natural source was proposed. This led to the creation of the decimal-based metric system in 1795, establishing a set of standards for other types of measurements.
Jean Baptiste Joseph DelambreJean Baptiste Joseph, chevalier Delambre (19 September 1749 – 19 August 1822) was a French mathematician, astronomer, historian of astronomy, and geodesist. He was also director of the Paris Observatory, and author of well-known books on the history of astronomy from ancient times to the 18th century. After a childhood fever, he suffered from very sensitive eyes, and believed that he would soon go blind. For fear of losing his ability to read, he devoured any book available and trained his memory.
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.
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.
