Jean Picard

Last updated
Jean-Felix Picard
CS Sorbonne Picard.jpg
Jean Picard sundial on the pediment of the Sorbonne
Born(1620-07-21)21 July 1620
La Flèche, Kingdom of France
Died12 July 1682(1682-07-12) (aged 61)
Paris, Kingdom of France
Occupation Astronomer
Notable workMesure de la Terre

Jean-Félix Picard (21 July 1620 12 July 1682) was a French astronomer and priest born in La Flèche, where he studied at the Jesuit Collège Royal Henry-Le-Grand. He died in Paris, France.

France Republic with mainland in Europe and numerous oversea territories

France, officially the French Republic, is a country whose territory consists of metropolitan France in Western Europe and several overseas regions and territories. The metropolitan area of France extends from the Mediterranean Sea to the English Channel and the North Sea, and from the Rhine to the Atlantic Ocean. It is bordered by Belgium, Luxembourg and Germany to the northeast, Switzerland and Italy to the east, and Andorra and Spain to the south. The overseas territories include French Guiana in South America and several islands in the Atlantic, Pacific and Indian oceans. The country's 18 integral regions span a combined area of 643,801 square kilometres (248,573 sq mi) and a total population of 67.3 million. France, a sovereign state, is a unitary semi-presidential republic with its capital in Paris, the country's largest city and main cultural and commercial centre. Other major urban areas include Lyon, Marseille, Toulouse, Bordeaux, Lille and Nice.

Astronomer scientist who studies celestial bodies

An astronomer is a scientist in the field of astronomy who focuses their studies on a specific question or field outside the scope of Earth. They observe astronomical objects such as stars, planets, moons, comets, and galaxies – in either observational or theoretical astronomy. Examples of topics or fields astronomers study include planetary science, solar astronomy, the origin or evolution of stars, or the formation of galaxies. Related but distinct subjects like physical cosmology, which studies the Universe as a whole.

La Flèche Subprefecture and commune in Pays de la Loire, France

La Flèche is a town and commune in the French department of Sarthe, in the Pays de la Loire region in the Loire Valley. It is the sub-prefecture of the South-Sarthe, the chief district and the chief city of a canton, and the second most populous city of the department. The city is part of the Community of communes of the Pays La Flèche. The inhabitants of the town are called the La Flèchois. It is classified as a country of art and history.


He is principally notable for his accurate measure the size of the Earth, based on a careful survey of one degree of latitude along the Paris Meridian.


Picard was the first person to measure the size of the Earth to a reasonable degree of accuracy in a survey conducted in 166970, for which he is honored with a pyramid at Juvisy-sur-Orge. Guided by Maurolycus's methodology and Snellius's mathematics for doing so, Picard achieved this by measuring one degree of latitude along the Paris Meridian using triangulation along thirteen triangles stretching from Paris to the clocktower of Sourdon, near Amiens.

Earth Third planet from the Sun in the Solar System

Earth is the third planet from the Sun and the only astronomical object known to harbor life. According to radiometric dating and other sources of evidence, Earth formed over 4.5 billion years ago. Earth's gravity interacts with other objects in space, especially the Sun and the Moon, Earth's only natural satellite. Earth revolves around the Sun in 365.26 days, a period known as an Earth year. During this time, Earth rotates about its axis about 366.26 times.

Pyramid structure whose shape is roughly that of a pyramid in the geometric sense

A pyramid is a structure whose outer surfaces are triangular and converge to a single point at the top, making the shape roughly a pyramid in the geometric sense. The base of a pyramid can be trilateral, quadrilateral, or of any polygon shape. As such, a pyramid has at least three outer triangular surfaces. The square pyramid, with a square base and four triangular outer surfaces, is a common version.

Juvisy-sur-Orge Commune in Île-de-France, France

Juvisy-sur-Orge is a commune in the Essonne department in Île-de-France in northern France. It is located 18 km south-east of Paris.

His measurements produced a result of 110.46 km for one degree of latitude, which gives a corresponding terrestrial radius of 6328.9 km. Isaac Newton was to use this value in his theory of universal gravitation.

Latitude The angle between zenith at a point and the plane of the equator

In geography, latitude is a geographic coordinate that specifies the north–south position of a point on the Earth's surface. Latitude is an angle which ranges from 0° at the Equator to 90° at the poles. Lines of constant latitude, or parallels, run east–west as circles parallel to the equator. Latitude is used together with longitude to specify the precise location of features on the surface of the Earth. On its own, the term latitude should be taken to be the geodetic latitude as defined below. Briefly, geodetic latitude at a point is the angle formed by the vector perpendicular to the ellipsoidal surface from that point, and the equatorial plane. Also defined are six auxiliary latitudes which are used in special applications.

Radius segment in a circle or sphere (from its center to its perimeter or surface) and its length

In classical geometry, a radius of a circle or sphere is any of the line segments from its center to its perimeter, and in more modern usage, it is also their length. The name comes from the Latin radius, meaning ray but also the spoke of a chariot wheel. The plural of radius can be either radii or the conventional English plural radiuses. The typical abbreviation and mathematical variable name for radius is r. By extension, the diameter d is defined as twice the radius:

Isaac Newton Influential British physicist and mathematician

Sir Isaac Newton was an English mathematician, physicist, astronomer, theologian, and author who is widely recognised as one of the most influential scientists of all time, and a key figure in the scientific revolution. His book Philosophiæ Naturalis Principia Mathematica, first published in 1687, laid the foundations of classical mechanics. Newton also made seminal contributions to optics, and shares credit with Gottfried Wilhelm Leibniz for developing the infinitesimal calculus.

The polar radius has now been measured at just over 6357 km. This was an error only 0.44% less than the modern value. This was another example of advances in astronomy and its tools making possible advances in cartography.

Astronomy natural science that deals with the study of celestial objects

Astronomy is a natural science that studies celestial objects and phenomena. It applies mathematics, physics, and chemistry in an effort to explain the origin of those objects and phenomena and their evolution. Objects of interest include planets, moons, stars, nebulae, galaxies, and comets; the phenomena also includes supernova explosions, gamma ray bursts, quasars, blazars, pulsars, and cosmic microwave background radiation. More generally, all phenomena that originate outside Earth's atmosphere are within the purview of astronomy. A related but distinct subject is physical cosmology, which is the study of the Universe as a whole.

Cartography The study and practice of making maps

Cartography is the study and practice of making maps. Combining science, aesthetics, and technique, cartography builds on the premise that reality can be modeled in ways that communicate spatial information effectively.


Picard was the first to attach a telescope with crosswires (developed by William Gascoigne) to a quadrant, and one of the first to use a micrometer screw on his instruments. The quadrant he used to determine the size of the Earth had a radius of 38 inches and was graduated to quarter-minutes. The sextant he used to find the meridian had a radius of six feet, and was equipped with a micrometer to enable minute adjustments. These equipment improvements made the margin of error only ten seconds, as opposed to Tycho Brahe's four minutes of error. This made his measurements 24 times as accurate.

Telescope Optical instrument that makes distant objects appear magnified

A telescope is an optical instrument that makes distant objects appear magnified by using an arrangement of lenses or curved mirrors and lenses, or various devices used to observe distant objects by their emission, absorption, or reflection of electromagnetic radiation. The first known practical telescopes were refracting telescopes invented in the Netherlands at the beginning of the 17th century, by using glass lenses. They were used for both terrestrial applications and astronomy.

William Gascoigne (scientist) English astronomer, mathematician and instrument maker

William Gascoigne was an English astronomer, mathematician and maker of scientific instruments from Middleton, Leeds who invented the micrometer. He was one of a group of astronomers in the north of England who followed the astronomy of Johannes Kepler which included, Jeremiah Horrocks and William Crabtree.

Quadrant (instrument) navigation instrument

A quadrant is an instrument that is used to measure angles up to 90°. Different versions of this instrument could be used to calculate various readings, such as longitude, latitude, and time of day. It was originally proposed by Ptolemy as a better kind of astrolabe. Several different variations of the instrument were later produced by medieval Muslim astronomers.

Other work

Picard also travelled to Tycho Brahe's Danish observatory, Uraniborg, in order to assess its position accurately so that Tycho's readings could be compared to others.

Tycho Brahe Danish astronomer and alchemist

Tycho Brahe was a Danish nobleman, astronomer, and writer known for his accurate and comprehensive astronomical and planetary observations. He was born in the then Danish peninsula of Scania. Well known in his lifetime as an astronomer, astrologer and alchemist, he has been described as "the first competent mind in modern astronomy to feel ardently the passion for exact empirical facts." His observations were some five times more accurate than the best available observations at the time.

Uraniborg historic observatory

Uraniborg was a Danish astronomical observatory and alchemy laboratory established and operated by Tycho Brahe. It was built c. 1576 – c. 1580 on Hven, an island in the Øresund between Zealand and Scania, which was part of Denmark at the time. It was expanded with the underground facility Stjerneborg on an adjacent site.

Picard collaborated and corresponded with many scientists, including Isaac Newton, Christiaan Huygens, Ole Rømer, Rasmus Bartholin, Johann Hudde, [1] and even his main competitor, Giovanni Cassini, although Cassini was often less than willing to return the gesture. These correspondences led to Picard's contributions to areas of science outside the field of geodesy, such as the aberration of light he observed while in Uraniborg, or his discovery of mercurial phosphorescence upon his observance of the faint glowing of a barometer. [2] This discovery led to Newton's studies of light's visible spectrum.

Picard also developed what became the standard method for measuring the right ascension of a celestial object. [3] [4] In this method, the observer records the time at which the object crosses the observer's meridian. Picard made his observations using the precision pendulum clock that Dutch physicist Christiaan Huygens had recently developed.


See also


  1. Johann (or Jan) van Waveren Hudde (1628–1704), mayor of Amsterdam, mathematician, lens maker. See:
  2. "Experience faire à l'Observatoire sur la Barometre simple touchant un nouveau Phenomene qu'on y a découvert" (Experiment done at the [Paris] observatory on a simple barometer concerning a new phenomenon that was discovered there), Le Journal des Sçavans [later: Journal des Savants ], page 112 (Paris edition) or page 126 (Amsterdam edition) (25 May 1676). Available on-line (in French) at: Gallica. See also: "Sur la lumière du baromètre" [On the light of the barometer], Histoire de l'Académie Royale des sciences de Paris, pages 202203 (1694). For further information, see: Barometric light.
  3. Picard did not conceive the method of measuring a celestial body's right ascension by recording the time at which the body crossed the observer’s meridian. According to French astronomer Camille Guillaume Bigourdan (1851-1932), the French astronomers Adrien Auzout (1622-1691) and Jacques Buot (or Buhot) (<1623-1678), the Dutch physicist Christiaan Huygens (1629-1695), the Czech physician/astronomer Hagecius (1525-1600) had all suggested the method ; even the ancient Greek astronomer Hipparchus (190 B.C.E.-120 B.C.E.) had hinted at it. However, the method had never been put into practice because it required both a telescope in place of the traditional sight of a quadrant and a very accurate clock. Picard was the first astronomer to actually employ the method. [G. Bigourdan (1917) "Sur l'emplacement et les coordonées de l'Observatoire de la porte Montmartre" (On the site and coordinates of the observatory by the Montmartre gate), Comptes rendus, vol. 164, pages 537-543.] In October 1669, Picard sent, to the Royal Academy of Sciences in Paris, a report of his celestial observations during the preceding year, which included the observation of two bright stars, Regulus and Arcturus, while the sun was still in the sky. The report was recorded in the Registres des Procès-verbaux de l‘Académie des Sciences. On reading the report, it becomes apparent that Picard had been using clocks to determine the right ascension of stars. French astronomer Pierre Charles Le Monnier (1715-1799) records an extract of Picard’s report and then remarks: "Cette Observation est remarquable, étant inoüi qu'on eût jamais pris la Hauteur Méridienne des Etoiles fixes non seulment en plein Soleil, mais pas même encore dans la force du Crépuscle ; desorte qu'il est maintenant facile (continue M. Picard) de trouver immédiatement les Ascensions droites des Etoiles fixes non seulment par les Horloges à Pendule, mais aussi par l'Observation du Vertical du Soleil au mème temps qu'on observera la hauteur Méridienne d'une Etoile fixe." (This observation is remarkable, it being unheard of that one has ever taken the meridian altitude of fixed stars not only in full sun, but still not in the force of twilight; so it is now easy (continues Mr. Picard) to find immediately the right ascensions of the fixed stars not only by pendulum clocks but also by observation of the vertical of the sun at the same time that one observes the meridian altitude of a fixed star.) [Pierre-Charles Le Monnier, Histoire céleste, ou Recueil de toutes les observations astronomiques faites par ordre du Roi … (Paris, France: Briasson, 1741), page 40.]
  4. Wolf, Abraham, A History of Science, Technology, and Philosophy in the 16th and 17th Centuries, vol. 2 (London, England: George Allen and Unwin, 1950), page 172.

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