Man has always been interested in the Earth on which he lives. During very early times this interest was limited, naturally, to the immediate vicinity of his home; later it expanded to the distance of markets or exchange places; and finally, with the development of means of transportation man became interested in his whole world. Much of this early "world interest" was evidenced by speculation concerning the size, shape, and composition of the Earth. Adjectives: Terrestrial, Terran, Telluric, Tellurian, Earthly Atmosphere Surface pressure: 101. ...

Early concepts of the figure of the Earth

Primitive ideas about the figure of the Earth, still found in young children, hold the Earth to be flat, and the heavens a physical dome spanning over it. Lunar eclipses, e.g., always have a circular edge of approx. three times the radius of the lunar disc; as these always happen when the Earth is between Sun and Moon, it suggests that the object casting the shadow is the Earth and must be spherical (and four times the size of the Moon, the lunar and solar discs being the same size). Also an astronomical event like a lunar eclipse which happened high in the sky in one end of the Mediterranean world, was close to the horizon in the other end, again suggesting curvature of the Earth's surface. The Sun is the star at the center of the Solar System. ... Apparent magnitude: up to -12. ... Time lapse movie of the 3 March 2007 lunar eclipse A lunar eclipse occurs whenever the Moon passes through some portion of the Earths shadow. ...

Classical Greece

The early Greeks, in their speculation and theorizing, ranged from the flat disc advocated by Homer to the spherical body postulated by Pythagoras — an idea supported one hundred years later by Aristotle. Pythagoras was a mathematician and to him the most perfect figure was a sphere. He reasoned that the gods would create a perfect figure and therefore the earth was created to be spherical in shape. Anaximenes, an early Greek scientist, believed strongly that the earth was rectangular in shape. Homer (Greek: , ) was an early Greek poet and aoidos (rhapsode) traditionally credited with the composition of the Iliad and the Odyssey. ... Pythagoras of Samos (Greek: ; circa 580 BC – circa 500 BC) was an Ionian (Greek) philosopher[1] and founder of the religious movement called Pythagoreanism. ... Aristotle (Greek: AristotélÄ“s) (384 BC – March 7, 322 BC) was a Greek philosopher, a student of Plato and teacher of Alexander the Great. ... A sphere is a perfectly symmetrical geometrical object. ... Anaximenes was the name of several notable people in ancient Greece. ...

Since the spherical shape was the most widely supported during the Greek Era, efforts to determine its size followed. Plato determined the circumference of the earth to be 40,000 miles while Archimedes estimated 30,000 miles. Plato's figure was a guess and Archimedes' a more conservative approximation. Meanwhile, in Egypt, a Greek scholar and philosopher, Eratosthenes, set out to make more explicit measurements.evne though that he was sexy and handsome he was the best scientist on earth even if he was dead. -_- For other uses, see Plato (disambiguation). ... Archimedes (Greek: c. ... Eratosthenes (Greek ; 276 BC - 194 BC) was a Greek mathematician, geographer and astronomer. ...

She had observed that on the day of the summer. yes baby ~!. solstice, the midday sun shone to the bottom of a well in the town of Syene (Aswan). Figure 1. At the same time, he observed the sun was not directly overhead at Alexandria; instead, it cast a shadow with the vertical equal to 1/50th of a circle (7° 12'). To these observations, Eratosthenes applied certain "known" facts (1) that on the day of the summer solstice, the midday sun was directly over the line of the summer Tropic Zone (Tropic of Cancer) - Syene was therefore concluded to be on this line; (2) Alexandria and Syene lay on a direct north-south line. Legend has it that he had someone walk from Alexandria to Syene to measure the distance: that came out to be equal to 500 miles. A solstice is either of the two events of the year when the sun is at its greatest distance from the equatorial plane. ... Aswan (Arabic: أسوان Aswān) (, population 200,000) is a city in the south of Egypt, the capital of the Aswan Governorate. ... Alexandria (Greek: , Coptic: , Arabic: , Egyptian Arabic: Iskindireyya), (population of 3. ... World map showing the Tropic of Cancer The Tropic of Cancer, or Northern tropic, is one of the five major circles of latitude that mark maps of the Earth. ...

Eratosthenes' method for determining the size of the Earth

From these observations, measurements, and "known" facts, Eratosthenes concluded that, since the angular deviation of the sun from the vertical direction at Alexandria was also the angle of the subtended arc, the linear distance between Alexandria and Syene was 1/50 of the circumference of the Earth or 50 x 500 = 25,000 miles. The circumference of the Earth over the poles is 40000 km by definition, i.e. 24855 statute miles. The actual unit of measure used by Eratosthenes was called the "stadion" (see Ancient Greek units of measurement). No one knows for sure what the stadion that he used is in today's units. The measurements given above in miles were derived using one stadion equal to one-tenth statute mile. Image File history File links Download high-resolution version (646x900, 374 KB) taken from the public domain source Geodesy for the Layman at http://www. ... Image File history File links Download high-resolution version (646x900, 374 KB) taken from the public domain source Geodesy for the Layman at http://www. ... In astronomy, geography, geometry and related sciences and contexts, a direction passing by a given point is said to be vertical if it is locally aligned with the gradient of the gravity field, i. ... The factual accuracy of this article is disputed. ...

It is remarkable that such accuracy was obtained. His measurements had these inaccuracies: (1) although it is true that the sun at noon is directly overhead at the Tropic of Cancer on the day of the summer solstice, Syene is not exactly on the tropic of Cancer but 37 miles to the north; (2) the true distance between Alexandria and Syene is somewhat smaller than Eratosthenes had measured (453 miles instead of the reported 500); (3) Syene lies 3° 30' east of the meridian of Alexandria; (4) the difference of latitude between Alexandria and Syene is 7° 5' rather than the rounded (1/50 of a circle) value of 7° 12' that Eratosthenes obtained.

Another ancient measurement of the size of the earth was made by the Greek, Posidonius. He noted that the star Canopus was hidden from view in most parts of Greece but that it just grazed the horizon at Rhodes. Posidonius measured the elevation of Canopus at Alexandria and determined that the angle was 1/48th of circle. Assuming the distance from Alexandria to Rhodes to be 500 miles, he computed the circumference of the earth as 24,000 miles. While both his measurements were approximations when combined, one error compensated for another and he achieved a fairly accurate result. The bust of Posidonius as an older man depicts his character as a Stoic philosopher. ... Canopus (α Car / α Carinae / Alpha Carinae) is the brightest star in the southern constellation of Carina, and the second brightest star in the sky, with a visual magnitude of −0. ... Rhodes (Greek: Ρόδος (pron. ...

Ancient India

The great Indian mathematician Aryabhata (476 - 550 AD) was a pioneer of mathematical astronomy. He describes the earth as being spherical and that it rotates on its axis, among other things in his work Aryabhatia. Aryabhatiya is divided into four sections. Gitika,Ganitha (mathematics), Kalakriya (reckoning of time) and Gola (celestial sphere). The discovery that the earth rotates on its own axis from west to east is described in Aryabhatiya ( Gitika 3,6; Kalakriya 5; Gola 9,10;) [1]. For example he explained the apparent motion of heavenly bodies is only an illusion (Gola 9), with the following simile; Statue of Aryabhata on the grounds of IUCAA, Pune. ... Gola can refer to: Gola, an ethnic group native to Liberia; Gola, a British sporting goods manufacturer. ...

Just as a passenger in a boat moving downstream sees the stationary (trees on the river banks) as traversing upstream, so does an observer on earth see the fixed stars as movin g towards the west at exactly the same speed (at which the earth moves from west to east.

Aryabhatiya also estimates the circumfurence of Earth which is accurate to 1%, which is remarkable. Aryabhata gives the radius of planets in terms of the Earth-Sun distance as essentially their periods of rotation around the Sun. He also gave the correct explanation of lunar and solar eclipses and that the Moon shines by reflecting sunlight [2]. Āryabhatīya, an astronomical treastise, is the Magnum Opus and only extant work of the 5th century Indian Mathematician, Aryabhatta. ... Statue of Aryabhata on the grounds of IUCAA, Pune. ...

The Middle Ages

Revising the figures of Posidonius, another Greek philosopher determined 18,000 miles as the earth's circumference. This last figure was promulgated by Ptolemy through his world maps. The maps of Ptolemy strongly influenced the cartographers of the Middle Ages. It is probable that Christopher Columbus, using such maps, was led to believe that Asia was only 3 or 4 thousand miles west of Europe. It was not until the 15th century that his concept of the earth's size was revised. During that period the Flemish cartographer, Mercator, made successive reductions in the size of the Mediterranean Sea and all of Europe which had the effect of increasing the size of the earth. A medieval artists rendition of Claudius Ptolemaeus Claudius Ptolemaeus (Greek: ; ca. ... The Middle Ages formed the middle period in a traditional schematic division of European history into three ages: the classical civilization of Antiquity, the Middle Ages, and modern times, beginning with the Renaissance. ... Christopher Columbus (1451 – May 20, 1506) was a navigator and maritime explorer credited as the discoverer of the Americas. ... (14th century - 15th century - 16th century - other centuries) As a means of recording the passage of time, the 15th century was that century which lasted from 1401 to 1500. ... Gerardus Mercator (March 5, 1512 – December 2, 1594) was a Flemish cartographer. ... Composite satellite image of the Mediterranean Sea. ...

Scientific revolution

The invention of the telescope and the theodolite and the development of logarithm tables allowed exact triangulation and grade measurement. The event which most historians of science call the scientific revolution can be dated roughly as having begun in 1543, the year in which Nicolaus Copernicus published his De revolutionibus orbium coelestium (On the Revolutions of the Heavenly Spheres) and Andreas Vesalius published his De humani corporis fabrica (On the... A telescope (from the Greek tele = far and skopein = to look or see; teleskopos = far-seeing) is an instrument designed for the observation of remote objects. ... An optical theodolite, manufactured in the Soviet Union in 1958 and used for topographic surveying. ... The common logarithm is the logarithm with base 10. ... Triangulation can be used to find the distance from the shore to the ship. ... Grade measurement is the geodetic determination of the local radius of curvature of the figure of the Earth by determining the difference in astronomical latitude between two locations on the same meridian, the metric distance between which is known. ...

Jean Picard performed the first modern arc measurement. He measured a base line by the aid of wooden rods, used a telescope in his angle measurements, and computed with logarithms. Jacques Cassini later continued Picard's arc northward to Dunkirk and southward to the Spanish boundary. Cassini divided the measured arc into two parts, one northward from Paris, another southward. When he computed the length of a degree from both chains, he found that the length of one degree in the northern part of the chain was shorter than that in the southern part. Figure 2. Jean-Felix Picard (July 21, 1620 – July 12, 1682) was a French astronomer and priest born in La Fleche. ... In typography and penmanship, the baseline is the line upon which most letters sit and under which descenders extend. ... Jacques Cassini (February 8, 1677 - April 18, 1756) was a French astronomer, son of Giovanni Domenico Cassini Cassini was born at the Paris Observatory. ... Location within France For the battleship, see Dunkerque Dunkirk (French: Dunkerque; Dutch: Duinkerke; German: Dünkirchen) is a harbour city and a commune in the northernmost part of France, in the département of Nord, 10 km from the Belgian border. ... City flag City coat of arms Motto: Fluctuat nec mergitur (Latin: Tossed by the waves, she does not sink) Paris Eiffel tower as seen from the esplanade du Trocadéro. ...

Cassini's ellipsoid; Huygens' theoretical ellipsoid

This result, if correct, meant that the earth was not a sphere, but an oblong (egg-shaped) ellipsoid -- which contradicted the computations by Isaac Newton and Christiaan Huygens. Newton's theory of gravitation predicted the Earth to be an oblate ellipsoid flattened at the poles to a ratio of 1:230. Image File history File links Download high-resolution version (623x900, 190 KB) taken from the public domain source Geodesy for the Layman at http://www. ... Image File history File links Download high-resolution version (623x900, 190 KB) taken from the public domain source Geodesy for the Layman at http://www. ... In geometry, a rectangle is a defined as a quadrilateral polygon in which all four angles are right angles. ... 3D rendering of an ellipsoid In mathematics, an ellipsoid is a type of quadric that is a higher dimensional analogue of an ellipse. ... Sir Isaac Newton, (4 January 1643 – 31 March 1727) [ OS: 25 December 1642 – 20 March 1727][1] was an English physicist, mathematician, astronomer, natural philosopher, and alchemist, regarded by many as the greatest figure in the history of science. ... Christiaan Huygens (pronounced in English (IPA): ; in Dutch: ) (April 14, 1629 – July 8, 1695), was a Dutch mathematician, astronomer and physicist; born in The Hague as the son of Constantijn Huygens. ... It has been suggested that this article or section be merged into Gravity. ... An oblate spheroid is ellipsoid having a shorter axis and two equal longer axes. ...

The issue could be settled by measuring, for a number of points on earth, the relationship between their distance (in north-south direction) and the angles between their astronomical verticals (the projection of the vertical direction on the sky). On an oblate Earth the distance corresponding to one degree would grow toward the poles. In astronomy, geography, geometry and related sciences and contexts, a direction passing by a given point is said to be vertical if it is locally aligned with the gradient of the gravity field, i. ...

The French Academy of Sciences dispatched two expeditions. One expedition under Pierre Louis Maupertuis (1736-37) was sent to Lapland (as far North as possible). The second mission under Pierre Bouguer was sent to what is modern-day Ecuador, near the equator (1735-44). Louis XIV visiting the Académie in 1671 The French Academy of Sciences (Académie des sciences) is a learned society, founded in 1666 by Louis XIV at the suggestion of Jean-Baptiste Colbert, to encourage and protect the spirit of French scientific research. ... Pierre Louis Maupertuis, here wearing lapmudes or a fur coat from his Lapland expedition. ... Events January 26 - Stanislaus I of Poland abdicates his throne. ... National anthem Sámi soga lávlla Languages Sami, Norwegian, Swedish, Finnish, Russian Area ca. ... // The French Geodesic Mission (also called the First Geodesic Mission and the Spanish-French Geodesic Mission) was an 18th-century expedition to Ecuador carried out for the purpose of measuring the roundness of the Earth and measuring the length of a degree of longitude at the Equator. ... Pierre Bouguer (February 16, 1698 – August 15, 1758) was a French mathematician. ... Events April 16 - The London premiere of Alcina by George Frideric Handel, his first the first Italian opera for the Royal Opera House at Covent Garden. ...

The measurements conclusively showed that the earth was oblate, with a ratio of 1:210. Thus the next approximation to the true figure of the Earth after the sphere became the oblong ellipsoid of revolution.

In South America Bouguer noticed, as did George Everest in India, that the astronomical vertical tended to be "pulled" in the direction of large mountain ranges, obviously due to the gravitational attraction of these huge piles of rock. As this vertical is everywhere perpendicular to the idealized surface of mean sea level, or the geoid, this means that the figure of the Earth is even more irregular than an ellipsoid of revolution. Thus the study of the "undulations of the geoid" became the next great undertaking in the science of studying the figure of the Earth. South America South America is a continent crossed by the equator, with most of its area in the Southern Hemisphere. ... Photograph of Everest Colonel Sir George Everest (July 4, 1790 - December 1, 1866) was a British surveyor and geographer, and Surveyor-General of India from 1830 to 1843. ... “Gravity” redirects here. ... The GOCE project will measure high-accuracy gravity gradients and provide an accurate geoid model based on the Earths gravity field. ...

19th century

Archive with lithography plates for maps of Bavaria in the Landesamt für Vermessung und Geoinformation in Munich

Negative litography stone and positive print of a historic map of Munich

In the late 19th century the Zentralbüro für die Internationale Erdmessung (that is, Central Bureau for International Geodesy) was established by Austria-Hungary and Germany. One of its most important goals was the derivation of an international ellipsoid and a gravity formula which should be optimal not only for Europe but also for the whole world. The Zentralbüro was an early predecessor of the International Association for Geodesy (IAG) and the International Union of Geodesy and Geophysics (IUGG) which was founded in 1919. Image File history File links Download high resolution version (1600x1200, 518 KB) Archive of the Landesamt für Vermessung und Geoinformation, containing a couple of hindred tons of stone litography plates with maps of Bavaria Picture taken as part of the Lange Nacht der Museen in Munich See also Image... Image File history File links Download high resolution version (1600x1200, 518 KB) Archive of the Landesamt für Vermessung und Geoinformation, containing a couple of hindred tons of stone litography plates with maps of Bavaria Picture taken as part of the Lange Nacht der Museen in Munich See also Image... Lithography stone and mirror-image print of a map of Munich. ... The geographic region and Free State of Bavaria (German:  ), with an area of 70,553 km² (27,241 square miles) and 12. ... Munich (German: , pronounced  ; Austro-Bavarian: Minga [1]) is the capital of the German Federal State of Bavaria. ... Image File history File links Download high resolution version (2294x1025, 504 KB) Two pictures showing the negative litography stone and the resulting positive print, with an old map of Munich. ... Image File history File links Download high resolution version (2294x1025, 504 KB) Two pictures showing the negative litography stone and the resulting positive print, with an old map of Munich. ... Munich (German: , pronounced  ; Austro-Bavarian: Minga [1]) is the capital of the German Federal State of Bavaria. ... Alternative meaning: Nineteenth Century (periodical) (18th century — 19th century — 20th century — more centuries) As a means of recording the passage of time, the 19th century was that century which lasted from 1801-1900 in the sense of the Gregorian calendar. ... Austria-Hungary, also known as the Dual monarchy (or: the k. ... 3D rendering of an ellipsoid In mathematics, an ellipsoid is a type of quadric that is a higher dimensional analogue of an ellipse. ... Gravity is a force of attraction that acts between bodies that have mass. ... World map showing the location of Europe. ... The International Union of Geodesy and Geophysics, or IUGG, is a non-governmental organisation dedicated to the scientific study of the Earth and to the application of the knowledge gained to the needs of society that was established in 1919. ... Year 1919 (MCMXIX) was a common year starting on Wednesday (link will display the full calendar). ...

Most of the relevant theories were derived by the German geodesist F.R. Helmert in his famous books Die mathematischen und physikalischen Theorien der höheren Geodäsie (1880). Helmert also derived the first global ellipsoid in 1906 with an accuracy of 100 meters (0.002 percent of the Earth's radii). The US geodesist Hayford derived a global ellipsoid in ~1910, based on intercontinental isostasy and an accuracy of 200 m. It was adopted by the IUGG as "international ellipsoid 1924". Friedrich Robert Helmert (* July 31, 1843 in Freiberg, Saxonia; † June 15, 1917 in Potsdam) was a celebrated German geodesist and an important writer on the theory of errors. ... Year 1880 (MDCCCLXXX) was a leap year starting on Thursday (link will display the full calendar). ... 1906 (MCMVI) was a common year starting on Monday (see link for calendar). ... Motto: (Out Of Many, One) (traditional) In God We Trust (1956 to date) Anthem: The Star-Spangled Banner Capital Washington D.C. Largest city New York City None at federal level (English de facto) Government Federal constitutional republic  - President George Walker Bush (R)  - Vice President Dick Cheney (R) Independence from... John Fillmore Hayford (1868-1925), eminent United States geodesist. ... Isostasy is a term used in Geology to refer to the state of gravitational equilibrium between the Earths lithosphere and asthenosphere such that the tectonic plates float at an elevation which depends on their thickness and density. ...

See also

• J.L. Greenberg: The problem of the Earth's shape from Newton to Clairaut: the rise of mathematical science in eighteenth-century Paris and the fall of "normal" science. Cambridge : Cambridge University Press, 1995 ISBN 0-521-38541-5

• M.R. Hoare: Quest for the true figure of the Earth: ideas and expeditions in four centuries of geodesy. Burlington, VT: Ashgate, 2004 ISBN 0-7546-5020-0

About this article

An early version of this article was taken from the public domain source at http://www.ngs.noaa.gov/PUBS_LIB/Geodesy4Layman/TR80003A.HTM#ZZ4 -- please update as necessary.

The next article in this series is mirrored in figure of the Earth. The expression figure of the Earth has various meanings in geodesy according to the way it is used and the precision with which the Earths size and shape is to be defined. ...