astronomy

Jean Picard

Jean Picard is a astronomy topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand Jean Picard rather than just read about it. In short: Jean Picard (French pronunciation: [ʒɑ̃ pikaʁ]; 21 July 1620 – 12 July 1682) was a French priest, astronomer and pioneer in geodesy, born in La Flèche, where he studied at the Collège royal Henri le Grand. He is best known for accurately measuring the size of the Earth, through a survey of one degree of latitude along the Paris Meridian.

Key takeaways

Jean Picard belongs to astronomy; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect Jean Picard to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Jean Picard from memory before moving on to harder problems.

Reference excerpt

Jean Picard (French pronunciation: [ʒɑ̃ pikaʁ]; 21 July 1620 – 12 July 1682) was a French priest, astronomer and pioneer in geodesy, born in La Flèche, where he studied at the Collège royal Henri le Grand. He is best known for accurately measuring the size of the Earth, through a survey of one degree of latitude along the Paris Meridian.

Geodesy Picard was the first to measure the size of the Earth with notable accuracy in a 1669–1670 arc measurement survey, for which he is commemorated by a pyramid at Juvisy-sur-Orge. Guided by Maurolycus's methodology and Willebrord Snellius's mathematics approach, he measured one degree of latitude along the Paris Meridian using triangulation across thirteen points from Paris to Sourdon, near Amiens. His calculations showed 110.46 km (68.64 mi) per degree of latitude, implying a radius of 6,328.9 km (3,932.6 mi). a figure later used by Isaac Newton in developing his theory of universal gravitation. Modern measurements put the polar radius about 6,357 km (3,950 mi), meaning Picard's result was only 0.44% lower than today's accepted value. A testament to how improved instruments advanced astronomy and cartography alike.

Instruments

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 (96.5 cm) and was graduated to quarter-minutes. The sextant he used to find the meridian had a radius of six feet (1.8 m) and had 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.

Other work In 1670–71, Picard travelled to the site of Tycho Brahe's Danish observatory, Uraniborg, in order to assess its longitude 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 he was 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 light's visible spectrum. 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.

Legacy There is a lunar crater named after Picard, on the southwest quadrant of Mare Crisium. The PICARD mission, an orbiting solar observatory, is named after Picard.

Works

Mesure de la Terre (1671). Voyage d'Uranibourg (in French). Paris: Imprimerie nationale. 1680. Traité du nivellement (in French). Paris: Estienne Michallet. 1684.

See also List of Roman Catholic scientist-clerics Meridian arc Seconds pendulum

Notes

External links O'Connor, John J.; Robertson, Edmund F., "Jean Picard", MacTutor History of Mathematics Archive, University of St Andrews Herbermann, Charles, ed. (1913). "Jean Picard" . Catholic Encyclopedia. New York: Robert Appleton Company. А.А.Гурштейн "Звезды Парижа" 2016. [1] Digital exhibition about Jean Picard (in French) / Observatoire de Paris

Illustrations

Worked examples

Example 1 — a first encounter with Jean Picard

Start with the simplest possible case. Write down what Jean Picard claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In astronomy, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Jean Picard before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Jean Picard ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Jean Picard

In research: Jean Picard appears in astronomy research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses Jean Picard in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: Jean Picard is common in secondary-school and first-year university syllabi. It links to neighbouring topics 1620 births, 1682 deaths, 17th-century French Roman Catholic priests, so understanding it makes those chapters shorter.
In everyday life: Look for Jean Picard outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

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How to study Jean Picard in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Jean Picard means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain Jean Picard out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Jean Picard in simple terms?

Why does Jean Picard matter?

Because it connects several astronomy ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Jean Picard?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Jean Picard.