Jean Picard
Encyclopedia
Jean-Felix Picard was a French
astronomer
and priest born in La Flèche
, where he studied at the Jesuit Collège Royal Henry-Le-Grand. He was the first person to measure the size of the Earth to a reasonable degree of accuracy in a survey conducted in 1669–70, 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. His measurements produced a result of 110.46 km for one degree of latitude, which gives a corresponding terrestrial radius
of 6328.9 km. 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. 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 more accurate. Isaac Newton
was to use this value in his theory of universal gravitation.
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'.
Picard collaborated and corresponded with many scientists, including Isaac Newton
, Christiaan Huygens, Ole Rømer, Rasmus Bartholin
, Johann Hudde, 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
. This discovery led to Newton's studies of spectrometry.
Picard also developed what became the standard method for measuring the right ascension
of a celestial object. 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.
His book "Mesure de la Terre" was published in 1671.
There is a lunar crater
named after Picard, on the northwest quadrant of Mare Crisium
.
The PICARD
mission, an orbiting solar observatory, is named after Picard.
France
The French Republic , The French Republic , The French Republic , (commonly known as France , is a unitary semi-presidential republic in Western Europe with several overseas territories and islands located on other continents and in the Indian, Pacific, and Atlantic oceans. Metropolitan France...
astronomer
Astronomer
An astronomer is a scientist who studies celestial bodies such as planets, stars and galaxies.Historically, astronomy was more concerned with the classification and description of phenomena in the sky, while astrophysics attempted to explain these phenomena and the differences between them using...
and priest born in La Flèche
La Flèche
La Flèche is a municipality located in the French department of Sarthe and the region of Pays de la Loire in the Loire Valley. This is the sub-prefecture of the South-Sarthe, the chief district and the chief city of a canton. This is the second most populous city of the department. The city is part...
, where he studied at the Jesuit Collège Royal Henry-Le-Grand. He was the first person to measure the size of the Earth to a reasonable degree of accuracy in a survey conducted in 1669–70, for which he is honored with a pyramid at Juvisy-sur-Orge
Juvisy-sur-Orge
Juvisy-sur-Orge is a commune in the Essonne department in Île-de-France in northern France.Inhabitants of Juvisy-sur-Orge are known as Juvisiens.-Geography:Neighboring communes:* Athis-Mons* Draveil* Savigny-sur-Orge* Viry-Châtillon...
. Guided by Maurolycus's methodology and Snellius
Willebrord Snellius
Willebrord Snellius was a Dutch astronomer and mathematician. In the west, especially the English speaking countries, his name has been attached to the law of refraction of light for several centuries, but it is now known that this law was first discovered by Ibn Sahl in 984...
's mathematics for doing so, Picard achieved this by measuring one degree of latitude along the Paris Meridian
Paris Meridian
The Paris Meridian is a meridian line running through the Paris Observatory in Paris, France—now longitude 2°20′14.025″ east. It was a long-standing rival to Greenwich as the prime meridian of the world, as was the Meridian of Antwerp in Antwerp, Belgium....
using triangulation along thirteen triangles stretching from Paris to the clocktower of Sourdon, near Amiens. His measurements produced a result of 110.46 km for one degree of latitude, which gives a corresponding terrestrial radius
Radius
In classical geometry, a radius of a circle or sphere is any line segment from its center to its perimeter. By extension, the radius of a circle or sphere is the length of any such segment, which is half the diameter. If the object does not have an obvious center, the term may refer to its...
of 6328.9 km. 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. Picard was the first to attach a telescope with crosswires (developed by William Gascoigne
William Gascoigne (scientist)
William Gascoigne was an English astronomer, mathematician and maker of scientific instruments from Middleton near Leeds who invented the micrometer...
) to a quadrant
Quadrant (instrument)
A quadrant is an instrument that is used to measure angles up to 90°. 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.-Types of quadrants:...
, 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
Tycho Brahe
Tycho Brahe , born Tyge Ottesen Brahe, was a Danish nobleman known for his accurate and comprehensive astronomical and planetary observations...
's four minutes of error. This made his measurements 24 times more accurate. Isaac Newton
Isaac Newton
Sir Isaac Newton PRS was an English physicist, mathematician, astronomer, natural philosopher, alchemist, and theologian, who has been "considered by many to be the greatest and most influential scientist who ever lived."...
was to use this value in his theory of universal gravitation.
Picard also travelled to Tycho Brahe
Tycho Brahe
Tycho Brahe , born Tyge Ottesen Brahe, was a Danish nobleman known for his accurate and comprehensive astronomical and planetary observations...
's Danish observatory, Uraniborg
Uraniborg
Uranienborg was a Danish astronomical observatory operated by Tycho Brahe; built circa 1576-1580 on Hven, an island in the Øresund between Zealand and Scania, which at that time was part of Denmark. The observatory was shortly after its construction expanded with an underground facility,...
, in order to assess its position accurately so that Tycho's readings could be compared to others'.
Picard collaborated and corresponded with many scientists, including Isaac Newton
Isaac Newton
Sir Isaac Newton PRS was an English physicist, mathematician, astronomer, natural philosopher, alchemist, and theologian, who has been "considered by many to be the greatest and most influential scientist who ever lived."...
, Christiaan Huygens, Ole Rømer, Rasmus Bartholin
Rasmus Bartholin
Rasmus Bartholin was a Danish scientist and physician. As part of his studies, he travelled in Europe for ten years. Professor at the University of Copenhagen, first in Geometry, later in Medicine...
, Johann Hudde, 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
Aberration of light
The aberration of light is an astronomical phenomenon which produces an apparent motion of celestial objects about their real locations...
he observed while in Uraniborg, or his discovery of mercurial phosphorescence
Phosphorescence
Phosphorescence is a specific type of photoluminescence related to fluorescence. Unlike fluorescence, a phosphorescent material does not immediately re-emit the radiation it absorbs. The slower time scales of the re-emission are associated with "forbidden" energy state transitions in quantum...
upon his observance of the faint glowing of a barometer
Barometer
A barometer is a scientific instrument used in meteorology to measure atmospheric pressure. Pressure tendency can forecast short term changes in the weather...
. This discovery led to Newton's studies of spectrometry.
Picard also developed what became the standard method for measuring the right ascension
Right ascension
Right ascension is the astronomical term for one of the two coordinates of a point on the celestial sphere when using the equatorial coordinate system. The other coordinate is the declination.-Explanation:...
of a celestial object. In this method, the observer records the time at which the object crosses the observer's meridian
Meridian (astronomy)
This article is about the astronomical concept. For other uses of the word, see Meridian.In the sky, a meridian is an imaginary great circle on the celestial sphere. It passes through the north point on the horizon, through the celestial pole, up to the zenith, through the south point on the...
. Picard made his observations using the precision pendulum clock
Pendulum clock
A pendulum clock is a clock that uses a pendulum, a swinging weight, as its timekeeping element. The advantage of a pendulum for timekeeping is that it is a resonant device; it swings back and forth in a precise time interval dependent on its length, and resists swinging at other rates...
that Dutch physicist Christiaan Huygens had recently developed.
His book "Mesure de la Terre" was published in 1671.
There is a lunar crater
Picard (crater)
Picard is a lunar impact crater that lies in Mare Crisium. To the west is the almost completely flooded crater Yerkes. Due east of Picard is the tiny Curtis. being slightly larger than Peirce to the north-northwest...
named after Picard, on the northwest quadrant of Mare Crisium
Mare Crisium
Mare Crisium is a lunar mare located in the Moon's Crisium basin, just northeast of Mare Tranquillitatis. This basin is of the Pre-Imbrian period, 4.55 to 3.85 billion years ago. This mare is in diameter, and 176,000 km2 in area. It has a very flat floor, with a ring of wrinkled ridges...
.
The PICARD
PICARD (spacecraft)
PICARD is a satellite dedicated to the simultaneous measurement of the absolute total and spectral solar irradiance, the diameter and solar shape, and to the Sun's interior probing by the helioseismology method. These measurements obtained throughout the mission will allow study of their variations...
mission, an orbiting solar observatory, is named after Picard.