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Christiaan Huygens, FRS (/ˈhaɪɡənz, ˈhɔɪɡənz/[3] HY-guns or HOY-guns; Dutch: [ˈɦœyɣə(n)s] ( listen); Latin: Hugenius; 14 April 1629 – 8 July 1695) was a Dutch physicist, mathematician, astronomer and inventor, who is widely regarded as one of the greatest scientists of all time and a major figure in the scientific revolution. He is known particularly as a physicist, astronomer, probabilist and horologist. In physics, Huygens made groundbreaking contributions in optics and mechanics, while as an astronomer Huygens is chiefly known for his studies of the rings of Saturn
Saturn
and the discovery of its moon Titan. As an inventor, Huygens improved the design of the telescope with the invention of the Huygenian eyepiece. His most famous invention, however, was the invention of the pendulum clock in 1656, which was a breakthrough in timekeeping and became the most accurate timekeeper for almost 300 years[citation needed]. Because he was the first to use mathematical formulae to describe the laws of physics, Huygens has been called the first theoretical physicist and the founder of mathematical physics.[4][5] In 1659, Huygens was the first to derive the now standard formula for the centripetal force in his work De vi centrifuga, a formula that was published in 1673 in the Horologium Oscillatorium, his book on pendulums. The formula played a central role in classical mechanics and became known as the second of Newton's laws of motion. Huygens was also the first to formulate the correct laws of elastic collision in his work De motu corporum ex percussion, but his findings weren't published until after his death in 1703. In the field of optics, Huygens is best known for his wave theory of light, which he proposed in 1678 and described in 1690 in his Traité de la lumière, which is regarded as the first mathematical theory of light. His theory, however, was initially rejected in favor of Newton's corpuscular theory of light, which explained light in terms of corpuscules. Until Augustin-Jean Fresnel
Augustin-Jean Fresnel
adopted Huygens' principle
Huygens' principle
in 1818 and showed that it could explain the rectilinear propagation and diffraction effects of light. Today this principle is known as the Huygens–Fresnel principle. Huygens invented the pendulum clock in 1656, which he patented the following year. In addition to inventing it, Huygens continued his research on pendulums and wrote in 1673 an extensive analysis of the pendulum in his book Horologium Oscillatorium, a major work on pendulums and horology, which is regarded as one of the three most important works done in mechanics in the 17th century. While the first part of the book contains a description of clock designs, the most part of the book is an extensive analysis of pendulum motion and a theory of curves. In 1655, Huygens began grinding lenses with his brother Constantijn in order to build telescopes to conduct astronomical research. Huygens designed a 50 power refracting telescope with which he discovered that the ring of Saturn
Saturn
was 'a thin, flat ring, nowhere touching, and inclined to the ecliptic.' It was with this telescope that Huygens also discovered the first of Saturn's moons, Titan. Huygens eventually developed in 1662 what is now called the Huygenian eyepiece, a telescope with two lenses, which diminished the amount of dispersion. As a mathematician, Huygens was a pioneer on probability and wrote his first treatise on probability theory in 1657 with the work Van Rekeningh in Spelen van Gluck. Frans van Schooten, who was the private tutor of Huygens, translated the work as De ratiociniis in ludo aleae ('On Reasoning in Games of Chance'). The work is a systematic treatise on probability and deals with games of chance and in particular the problem of points. The modern concept of probability grew out of the use of expectation values by Huygens and Blaise Pascal
Blaise Pascal
(who encouraged him to write the work). The last years of Huygens, who never married, were characterized by loneliness and depression. As a rationalist, Huygens refused to believe in an immanent supreme being and couldn't accept the Christian faith of his upbringing. Although Huygens didn't believe in such a supernatural being, he did hypothesize on the possibility of extraterrestrial life in his Cosmotheoros, which was published shortly before his death in 1695. Huygens speculated that extraterrestrial life was possible on planets similar to Earth and wrote that the availability of water in liquid form was a necessity for life.

Contents

1 Early life 2 Student years 3 Early correspondence 4 Scientific debut 5 In France 6 Later life 7 Work in natural philosophy

7.1 Laws of motion, impact and gravitation 7.2 Optics 7.3 Horology

7.3.1 Pendulums 7.3.2 Balance spring
Balance spring
watch

7.4 Astronomy

7.4.1 Saturn's rings
Saturn's rings
and Titan 7.4.2 Mars
Mars
and Syrtis Major 7.4.3 Cosmotheoros

8 Portraits

8.1 During his lifetime 8.2 Statues

9 Named after Huygens

9.1 Science 9.2 Other

10 Works 11 See also 12 Notes 13 References 14 Further reading 15 External links

15.1 Primary sources, translations 15.2 Museums 15.3 Other

Early life[edit]

Portrait of Huygens' father (centre) and his five children (Christiaan at right). Mauritshuis, The Hague.

Christiaan Huygens. Cut from the engraving following the painting of Caspar Netscher
Caspar Netscher
by G. Edelinck, between 1684 and 1687.

Christiaan Huygens
Christiaan Huygens
was born on 14 April 1629 in The Hague, into a rich and influential Dutch family,[6][7] the second son of Constantijn Huygens. Christiaan was named after his paternal grandfather.[8][9] His mother was Suzanna van Baerle. She died in 1637, shortly after the birth of Huygens' sister.[10] The couple had five children: Constantijn (1628), Christiaan (1629), Lodewijk (1631), Philips (1632) and Suzanna (1637).[11] Constantijn Huygens
Constantijn Huygens
was a diplomat and advisor to the House of Orange, and also a poet and musician. His friends included Galileo Galilei, Marin Mersenne
Marin Mersenne
and René Descartes.[12] Huygens was educated at home until turning sixteen years old. He liked to play with miniatures of mills and other machines. His father gave him a liberal education: he studied languages and music, history and geography, mathematics, logic and rhetoric, but also dancing, fencing and horse riding.[8][11][13] In 1644 Huygens had as his mathematical tutor Jan Jansz de Jonge Stampioen, who set the 15-year-old a demanding reading list on contemporary science.[14] Descartes was impressed by his skills in geometry.[7] Student years[edit] His father sent Huygens to study law and mathematics at the University of Leiden, where he studied from May 1645 to March 1647.[8] Frans van Schooten was an academic at Leiden
Leiden
from 1646, and also a private tutor to Huygens and his elder brother, replacing Stampioen on the advice of Descartes.[15][16] Van Schooten brought his mathematical education up to date, in particular introducing him to the work of Fermat on differential geometry.[17] After two years, from March 1647, Huygens continued his studies at the newly founded Orange College, in Breda, where his father was a curator: the change occurred because of a duel between his brother Lodewijk and another student.[18] Constantijn Huygens
Constantijn Huygens
was closely involved in the new College, which lasted only to 1669; the rector was André Rivet.[19] Christiaan Huygens
Christiaan Huygens
lived at the home of the jurist Johann Henryk Dauber, and had mathematics classes with the English lecturer John Pell. He completed his studies in August 1649.[8] He then had a stint as a diplomat on a mission with Henry, Duke of Nassau. It took him to Bentheim, then Flensburg. He took off for Denmark, visited Copenhagen
Copenhagen
and Helsingør, and hoped to cross the Øresund
Øresund
to visit Descartes in Stockholm. It was not to be.[20] While his father Constantijn had wished his son Christiaan to be a diplomat, it also was not to be. In political terms, the First Stadtholderless Period that began in 1650 meant that the House of Orange was not in power, removing Constantijn's influence. Further, he realised that his son had no interest in such a career.[21] Early correspondence[edit]

Correspondance

Huygens generally wrote in French or Latin.[22] While still a college student at Leiden
Leiden
he began a correspondence with the intelligencer Mersenne, who died quite soon afterwards in 1648.[8] Mersenne wrote to Constantijn on his son's talent for mathematics, and flatteringly compared him to Archimedes
Archimedes
(3 January 1647). The letters show the early interests of Huygens in mathematics. In October 1646 there is the suspension bridge, and the demonstration that a catenary is not a parabola.[23] In 1647/8 they cover the claim of Grégoire de Saint-Vincent to squaring the circle; rectification of the ellipse; projectiles, and the vibrating string.[24] Some of Mersenne's concerns at the time, such as the cycloid (he sent Evangelista Torricelli's treatise on the curve), the centre of oscillation, and the gravitational constant, were matters Huygens only took seriously towards the end of the 17th century.[25] Mersenne had also written on musical theory. Huygens preferred meantone temperament; he innovated in 31 equal temperament, which was not itself a new idea but known to Francisco de Salinas, using logarithms to investigate it further and show its close relation to the meantone system.[26] In 1654, Huygens returned to his father's house in The Hague, and was able to devote himself entirely to research.[8] The family had another house, not far away at Hofwijck, and he spent time there during the summer. His scholarly life did not allow him to escape bouts of depression.[27]

The garden plan at Hofwijck, 1653

Subsequently, Huygens developed a broad range of correspondents, though picking up the threads after 1648 was hampered by the five-year Fronde
Fronde
in France. Visiting Paris in 1655, Huygens called on Ismael Boulliau to introduce himself. Then Boulliau took him to see Claude Mylon.[28] The Parisian group of savants that had gathered around Mersenne held together into the 1650s, and Mylon, who had assumed the secretarial role, took some trouble from then on to keep Huygens in touch.[29] Through Pierre de Carcavi Huygens corresponded in 1656 with Pierre de Fermat, whom he admired greatly, though this side of idolatry. The experience was bittersweet and even puzzling, since it became clear that Fermat had dropped out of the research mainstream, and his priority claims could probably not be made good in some cases. Besides, Huygens was looking by then to apply mathematics, while Fermat's concerns ran to purer topics.[30] Scientific debut[edit] Huygens was often slow to publish his results and discoveries. In the early days his mentor Frans van Schooten
Frans van Schooten
was cautious for the sake of his reputation.[31] The first work Huygens put in print was Theoremata de quadratura (1651) in the field of quadrature. It included material discussed with Mersenne some years before, such as the fallacious nature of the squaring of the circle by Grégoire de Saint-Vincent. His preferred methods were those of Archimedes
Archimedes
and Fermat.[17] Quadrature was a live issue in the 1650s, and through Mylon, Huygens intervened in the discussion of the mathematics of Thomas Hobbes. Persisting in trying to explain the errors Hobbes had fallen into, he made an international reputation.[32]

The catenary in a manuscript of Huygens.

Huygens studied spherical lenses from a theoretical point of view in 1652–3, obtaining results that remained unpublished until Isaac Barrow (1669). His aim was to understand telescopes.[33] He began grinding his own lenses in 1655, collaborating with his brother Constantijn.[34] He designed in 1662 what is now called the Huygenian eyepiece, with two lenses, as a telescope ocular.[35][36] Lenses were also a common interest through which Huygens could meet socially in the 1660s with Baruch Spinoza, who ground them professionally. They had rather different outlooks on science, Spinoza
Spinoza
being the more committed Cartesian, and some of their discussion survives in correspondence.[37] He encountered the work of Antoni van Leeuwenhoek, another lens grinder, in the field of microscopy which interested his father.[38] Huygens wrote the first treatise on probability theory, De ratiociniis in ludo aleae ("On Reasoning in Games of Chance", 1657).[39] He had been told of recent work in the field by Fermat, Blaise Pascal
Blaise Pascal
and Girard Desargues
Girard Desargues
two years earlier, in Paris.[40] Frans van Schooten translated the original Dutch manuscript "Van Rekeningh in Spelen van Geluck" into Latin and published it in his Exercitationum mathematicarum. It deals with games of chance, in particular the problem of points. Huygens took as intuitive his appeals to concepts of a "fair game" and equitable contract, and used them set up a theory of expected values.[41] In 1662 Sir Robert Moray sent Huygens John Graunt's life table, and in time Huygens and his brother Lodewijk worked on life expectancy.[42] On 3 May 1661, Huygens observed the planet Mercury transit over the Sun, using the telescope of instrument maker Richard Reeve in London, together with astronomer Thomas Streete and Reeve.[43] Streete then debated the published record of the transit of Hevelius, a controversy mediated by Henry Oldenburg.[44] Huygens passed to Hevelius
Hevelius
a manuscript of Jeremiah Horrocks
Jeremiah Horrocks
on the transit of Venus, 1639, which thereby was printed for the first time in 1662.[45] In that year Huygens, who played the harpsichord, took an interest in music, and Simon Stevin's theories on it; he showed very little concern to publish his theories on consonance, some of which were lost for centuries.[46][47] The Royal Society of London
Royal Society of London
elected him a Fellow in 1663.[48] In France[edit] The Montmor Academy
Montmor Academy
was the form the old Mersenne circle took after the mid-1650s.[49] Huygens took part in its debates, and supported its "dissident" faction who favoured experimental demonstration to curtail fruitless discussion, and opposed amateurish attitudes.[50] During 1663 he made what was his third visit to Paris; the Montmor Academy closed down, and Huygens took the chance to advocate a more Baconian programme in science. In 1666 he moved to Paris and earned a position at Louis XIV's new French Academy of Sciences.[51] In Paris Huygens had an important patron and correspondent in Jean-Baptiste Colbert.[52] However, his relationship with the Academy was not always easy, and in 1670 Huygens, seriously ill, chose Francis Vernon to carry out a donation of his papers to the Royal Society
Royal Society
in London, should he die.[53] Then the Franco-Dutch War
Franco-Dutch War
took place (1672–8). England's part in it (1672–4) is thought to have damaged his relationship with the Royal Society.[54] Robert Hooke
Robert Hooke
for the Royal Society
Royal Society
lacked the urbanity to handle the situation, in 1673.[55]

Christiaan Huygens, relief by Jean-Jacques Clérion, around 1670?

Denis Papin
Denis Papin
was assistant to Huygens from 1671.[56] One of their projects, which did not bear fruit directly, was the gunpowder engine.[57] Papin moved to England in 1678, and continued to work in this area.[58] Using the Paris Observatory
Paris Observatory
(completed in 1672), Huygens made further astronomical observations. In 1678 he introduced Nicolaas Hartsoeker
Nicolaas Hartsoeker
to French scientists such as Nicolas Malebranche and Giovanni Cassini. It was in Paris, also, that Huygens met the young diplomat Gottfried Leibniz, there in 1672 on a vain mission to meet Arnauld de Pomponne, the French Foreign Minister. At this time Leibniz was working on a calculating machine, and he moved on to London in early 1673 with diplomats from Mainz; but from March 1673 Leibniz was tutored in mathematics by Huygens.[59] Huygens taught him analytical geometry; an extensive correspondence ensued, in which Huygens showed reluctance to accept the advantages of infinitesimal calculus.[60] Later life[edit] Huygens moved back to The Hague
The Hague
in 1681 after suffering serious depressive illness. In 1684, he published Astroscopia Compendiaria on his new tubeless aerial telescope. He attempted to return to France in 1685 but the revocation of the Edict of Nantes precluded this move. His father died in 1687, and he inherited Hofwijck, which he made his home the following year.[21]

Hofwijck, home to Christiaan Huygens
Christiaan Huygens
from 1688

On his third visit to England, in 1689, Huygens met Isaac Newton
Isaac Newton
on 12 June. They spoke about Iceland spar, and subsequently corresponded about resisted motion.[61] Huygens observed the acoustical phenomenon now known as flanging in 1693.[62] He died in The Hague
The Hague
on 8 July 1695, and was buried in the Grote Kerk.[63] Huygens never married.[64] Work in natural philosophy[edit] Huygens has been called the leading European natural philosopher between Descartes and Newton.[65] He adhered to the tenets of the mechanical philosophy of his time. In particular he sought explanations of the force of gravity that avoided action at a distance.[66] In common with Robert Boyle
Robert Boyle
and Jacques Rohault, Huygens adhered to what has been called, more explicitly, "experimentally oriented corpuscular-mechanical" natural philosophy. In the analysis of the Scientific Revolution
Scientific Revolution
this appears as a mainstream position, at least from the founding of the Royal Society
Royal Society
to the emergence of Newton, and was sometimes labelled "Baconian", while not being inductivist or identifying with the views of Francis Bacon
Francis Bacon
in a simple-minded way.[67] After his first visit to England in 1661, when he attended a meeting of the Gresham College group in April and learned directly about Boyle's air pump experiments, Huygens spent time in late 1661 and early 1662 replicating the work. It proved a long process, brought to the surface an experimental issue ("anomalous suspension") and the theoretical issue of horror vacui, and ended in July 1663 as Huygens became a Fellow of the Royal Society. It has been said that Huygens finally accepted Boyle's view of the void, as against the Cartesian denial of it;[68] and also (in Leviathan and the Air Pump) that the replication of results trailed off messily.[69] Newton's influence on John Locke
John Locke
was mediated by Huygens, who assured Locke that Newton's mathematics was sound, leading to Locke's acceptance of a "corpuscular-mechanical" physics.[70] Laws of motion, impact and gravitation[edit] The general approach of the mechanical philosophers was to postulate theories of the kind now called "contact action". Huygens adopted this method, but not without seeing its difficulties and failures.[71] Leibniz, his student in Paris, abandoned the theory.[72] Seeing the universe this way made the theory of collisions central to physics. The requirements of the mechanical philosophy, in the view of Huygens, were stringent. Matter in motion made up the universe, and only explanations in those terms could be truly intelligible. While he was influenced by the Cartesian approach, he was less doctrinaire.[73] He studied elastic collisions in the 1650s but delayed publication for over a decade.[17]

Depiction from Huygens, Oeuvres Complètes: a boating metaphor underlay the way of thinking about relative motion, and so simplifying the theory of colliding bodies

Huygens concluded quite early that Descartes's laws for the elastic collision of two bodies must be wrong, and he formulated the correct laws.[74] An important step was his recognition of the Galilean invariance of the problems.[75] His views then took many years to be circulated. He passed them on in person to William Brouncker and Christopher Wren
Christopher Wren
in London, in 1661.[76] What Spinoza
Spinoza
wrote to Henry Oldenburg about them, in 1666 which was during the Second
Second
Anglo-Dutch War, was guarded.[77] Huygens had actually worked them out in a manuscript De motu corporum ex percussione in the period 1652–6. The war ended in 1667, and Huygens announced his results to the Royal Society in 1668. He published them in the Journal des sçavans
Journal des sçavans
in 1669.[17] Huygens stated what is now known as the second of Newton's laws of motion in a quadratic form.[78] In 1659 he derived the now standard formula for the centripetal force, exerted on an object describing a circular motion, for instance by the string to which it is attached. In modern notation:

F

c

=

m  

v

2

r

displaystyle F_ c = frac m v^ 2 r

with m the mass of the object, v the velocity and r the radius. The publication of the general formula for this force in 1673 was a significant step in studying orbits in astronomy. It enabled the transition from Kepler's third law
Kepler's third law
of planetary motion, to the inverse square law of gravitation.[79] The interpretation of Newton's work on gravitation by Huygens differed, however, from that of Newtonians such as Roger Cotes; he did not insist on the a priori attitude of Descartes, but neither would he accept aspects of gravitational attractions that were not attributable in principle to contact of particles.[80] The approach used by Huygens also missed some central notions of mathematical physics, which were not lost on others. His work on pendulums came very close to the theory of simple harmonic motion; but the topic was covered fully for the first time by Newton, in Book II of his Principia Mathematica (1687).[81] In 1678 Leibniz picked out of Huygens's work on collisions the idea of conservation law that Huygens had left implicit.[82] Optics[edit] Huygens is remembered especially for his wave theory of light, which he first communicated in 1678 to the Paris Académie des sciences. It was published in 1690 in his Traité de la lumière[83] (Treatise on light[84]), making it the first mathematical theory of light. He refers to Ignace-Gaston Pardies, whose manuscript on optics helped him on his wave theory.[85] A basic principle of Huygens is that the speed of light is finite, a point which had been the subject of an experimental demonstration by Olaus Roemer (1679 at the Paris Observatory), but which Huygens is presumed to have believed already.[86] The theory is kinematic and its scope largely restricted to geometrical optics. It covers little of what would now be termed physical optics. It deals with wavefronts and their normal rays, with propagation conceived by means of spherical waves emitted along the wave front (see also Huygens–Fresnel principle).[87] It was justified as an ether theory, involving transmission via perfectly elastic particles, a revision of the view of Descartes. The nature of light was therefore a longitudinal wave.[86] Huygens had experimented in 1672 with double refraction (birefringence) in Icelandic spar (calcite), a phenomenon discovered in 1669 by Rasmus Bartholin. At first he could not elucidate what he found.[36] He later explained it[84] with his wave front theory and concept of evolutes. He also developed ideas on caustics.[88] Newton in his Opticks
Opticks
of 1704 proposed instead a corpuscular theory of light. The theory of Huygens was not accepted by some, because longitudinal waves cannot show birefringence. The interference experiments of Thomas Young vindicated a wave theory in 1801: the results could not be explained with light particles. The solution to the problem Huygens had faced was then resolved by a transverse wave theory.[89] For a view from modern physics see wave–particle duality. Huygens investigated the use of lenses in projectors. He is credited as the inventor of the magic lantern, described in correspondence of 1659.[90] There are others to whom such a lantern device has been attributed, such as Giambattista della Porta, and Cornelis Drebbel: the point at issue is the use of a lens for better projection. Athanasius Kircher
Athanasius Kircher
has also been credited for that.[91] Horology[edit] Huygens designed more accurate clocks than were available at the time. In 1656, inspired by earlier research into pendulums by Galileo Galilei, he invented the pendulum clock, which was a breakthrough in timekeeping and became the most accurate timekeeper for the next 275 years until the 1930s. Huygens contracted the construction of his clock designs to Salomon Coster in The Hague, with a local patent (octroy). He was less successful elsewhere: Pierre Séguier
Pierre Séguier
refused him any French rights, Simon Douw of Rotterdam
Rotterdam
copied the design in 1658, and Ahasuerus Fromanteel
Ahasuerus Fromanteel
also, in London.[92] The oldest known Huygens-style pendulum clock is dated 1657 and can be seen at the Museum Boerhaave
Museum Boerhaave
in Leiden.[93][94][95][96] Huygens motivation for inventing the pendulum clock was to create an accurate marine chronometer that could be used to find longitude by celestial navigation during sea voyages. Exploiting the invention at sea proved troublesome, however, because the rocking motion of the ship disturbed the motion of the pendulum. In 1660 Lodewijk Huygens made a trial on a voyage to Spain, and reported that heavy weather made the clock useless. Alexander Bruce elbowed into the field in 1662, and Huygens called in Sir Robert Moray and the Royal Society
Royal Society
to mediate and preserve some of his rights.[97] Trials continued into the 1660s, the best news coming from a Royal Navy captain Robert Holmes operating against the Dutch possessions in 1664.[98] Lisa Jardine
Lisa Jardine
[99] doubts that Holmes reported the results of the trial accurately, and Samuel Pepys expressed his doubts at the time: The said master [i.e. the captain of Holmes' ship] affirmed, that the vulgar reckoning proved as near as that of the watches, which [the clocks], added he, had varied from one another unequally, sometimes backward, sometimes forward, to 4, 6, 7, 3, 5 minutes; as also that they had been corrected by the usual account. One for the French Academy on an expedition to Cayenne
Cayenne
ended badly. Jean Richer suggested correction for the figure of the Earth. By the time of the Dutch East India Company expedition of 1686 to the Cape of Good Hope, Huygens was able to supply the correction retrospectively.[100] Pendulums[edit]

Spring driven pendulum clock, designed by Huygens, built by instrument maker Salomon Coster (1657),[101] and copy of the Horologium Oscillatorium,[102] Museum Boerhaave, Leiden

In 1673 Huygens published Horologium Oscillatorium sive de motu pendulorum, his major work on pendulums and horology. It had been observed by Mersenne and others that pendulums are not quite isochronous: their period depends on their width of swing, with wide swings taking slightly longer than narrow swings.[103][104] Huygens analyzed this problem by finding the curve down which a mass will slide under the influence of gravity in the same amount of time, regardless of its starting point; the so-called tautochrone problem. By geometrical methods which were an early use of calculus, he showed it to be a cycloid, rather than the circular arc of a pendulum's bob, and therefore that pendulums are not isochronous. He also solved a problem posed by Mersenne: how to calculate the period of a pendulum made of an arbitrarily shaped swinging rigid body. This involved discovering the center of oscillation and its reciprocal relationship with the pivot point. In the same work, he analysed the conical pendulum, consisting of a weight on a cord moving in a circle, using the concept of centrifugal force.

Detail of illustration from Horologium Oscillatorium (1658), by Huygens

Huygens clock, Rijksmuseum, Amsterdam

Huygens was the first to derive the formula for the period of an ideal mathematical pendulum (with massless rod or cord and length much longer than its swing), in modern notation:

T = 2 π

l g

displaystyle T=2pi sqrt frac l g

with T the period, l the length of the pendulum and g the gravitational acceleration. By his study of the oscillation period of compound pendulums Huygens made pivotal contributions to the development of the concept of moment of inertia.[78] Huygens also observed coupled oscillations: two of his pendulum clocks mounted next to each other on the same support often became synchronized, swinging in opposite directions. He reported the results by letter to the Royal Society, and it is referred to as "an odd kind of sympathy" in the Society's minutes.[105][106] This concept is now known as entrainment.

Experimental setup of Huygens synchronization of two clocks

Balance spring
Balance spring
watch[edit] Huygens developed a balance spring watch in the same period as, though independently of, Robert Hooke. Controversy over the priority persisted for centuries. A Huygens watch employed a spiral balance spring; but he used this form of spring initially only because the balance in his first watch rotated more than one and a half turns. He later used spiral springs in more conventional watches, made for him by Thuret in Paris from around 1675.

Huygens' explanation for the aspects of Saturn, Systema Saturnium, 1659.

Such springs were essential in modern watches with a detached lever escapement because they can be adjusted for isochronism. Watches in the time of Huygens and Hooke, however, employed the very undetached verge escapement. It interfered with the isochronal properties of any form of balance spring, spiral or otherwise. In February 2006, a long-lost copy of Hooke's handwritten notes from several decades of Royal Society
Royal Society
meetings was discovered in a cupboard in Hampshire, England. The balance-spring priority controversy appears, by the evidence contained in those notes, to be settled in favour of Hooke's claim.[107][108] In 1675, Huygens patented a pocket watch. The watches which were made in Paris from c. 1675 and following the Huygens plan are notable for lacking a fusee for equalizing the mainspring torque. The implication is that Huygens thought that his spiral spring would isochronise the balance, in the same way that he thought that the cycloidally shaped suspension curbs on his clocks would isochronise the pendulum. Astronomy[edit]

Huygens' telescope without tube. Picture from his 1684 Astroscopia Compendiaria tubi optici molimine liberata (compound telescopes without a tube)

Saturn's rings
Saturn's rings
and Titan[edit] In 1655, Huygens proposed that Saturn
Saturn
was surrounded by a solid ring, "a thin, flat ring, nowhere touching, and inclined to the ecliptic." Using a 50 power refracting telescope that he designed himself, Huygens also discovered the first of Saturn's moons, Titan.[109] In the same year he observed and sketched the Orion Nebula. His drawing, the first such known of the Orion nebula, was published in Systema Saturnium in 1659. Using his modern telescope he succeeded in subdividing the nebula into different stars. The brighter interior now bears the name of the Huygenian region in his honour.[110] He also discovered several interstellar nebulae and some double stars. Mars
Mars
and Syrtis Major[edit] In 1659, Huygens was the first to observe a surface feature on another planet, Syrtis Major, a volcanic plain on Mars. He used repeated observations of the movement of this feature over the course of a number of days to estimate the length of day on Mars, which he did quite accurately to 24 1/2 hours. This figure is only a few minutes off of the actual length of the Martian day of 24 hours, 37 minutes.[111] Cosmotheoros[edit] Shortly before his death in 1695, Huygens completed Cosmotheoros, published posthumously in 1698. In it he speculated on the existence of extraterrestrial life, on other planets, which he imagined was similar to that on Earth. Such speculations were not uncommon at the time, justified by Copernicanism
Copernicanism
or the plenitude principle. But Huygens went into greater detail,[112] though without the benefit of understanding Newton's laws of gravitation, or the fact that oxygen is necessary for life and distinct from other atmospheric gases.[113] The work, translated into English in its year of publication, has been seen as in the fanciful tradition of Francis Godwin, John Wilkins
John Wilkins
and Cyrano de Bergerac, and fundamentally Utopian; and also to owe in its concept of planet to cosmography in the sense of Peter Heylin.[114][115] Huygens wrote that availability of water in liquid form was essential for life and that the properties of water must vary from planet to planet to suit the temperature range. He took his observations of dark and bright spots on the surfaces of Mars
Mars
and Jupiter to be evidence of water and ice on those planets.[116] He argued that extraterrestrial life is neither confirmed nor denied by the Bible, and questioned why God would create the other planets if they were not to serve a greater purpose than that of being admired from Earth. Huygens postulated that the great distance between the planets signified that God had not intended for beings on one to know about the beings on the others, and had not foreseen how much humans would advance in scientific knowledge.[117] It was also in this book that Huygens published his method for estimating stellar distances. He made a series of smaller holes in a screen facing the sun, until he estimated the light was of the same intensity as that of the star Sirius. He then calculated that the angle of this hole was

1

/

27 , 664

displaystyle 1/27,664

th the diameter of the Sun, and thus it was about 30,000 times as far away, on the (incorrect) assumption that Sirius
Sirius
is as luminous as our sun. The subject of photometry remained in its infancy until Pierre Bouguer and Johann Heinrich Lambert.[118] Portraits[edit] During his lifetime[edit]

1639 – His father Constantijn Huygens
Constantijn Huygens
in the midst of his five children by Adriaen Hanneman, painting with medaillons, Mauritshuis, The Hague 1671 – Portrait by Caspar Netscher, Museum Boerhaave, Leiden, loan from Haags Historisch Museum ~1675 – Possible depiction of Huygens on l'French: Établissement de l' Académie des Sciences
Académie des Sciences
et fondation de l'observatoire, 1666 by Henri Testelin. Colbert presents the members of the newly founded Académie des Sciences to king Louis XIV
Louis XIV
of France. Musée National du Château et des Trianons de Versailles, Versailles 1679 – Medaillon portrait in relief by the French sculptor Jean-Jacques Clérion 1686 – Portrait in pastel by Bernard Vaillant, Museum Hofwijck, Voorburg between 1684 and 1687 – Engraving
Engraving
by G. Edelinck
G. Edelinck
after the painting by Caspar Netscher 1688 – Portrait by Pierre Bourguignon (painter), Royal Netherlands Academy of Arts and Sciences, Amsterdam

Statues[edit]

Rotterdam

Delft

Leiden

Haarlem

Voorburg

Named after Huygens[edit] Science[edit]

The Huygens probe: The lander for the Saturnian moon Titan, part of the Cassini–Huygens
Cassini–Huygens
mission to Saturn Asteroid 2801 Huygens A crater on Mars Mons Huygens, a mountain on the Moon Huygens Software, a microscope image processing package. A two element eyepiece designed by him. An early step in the development of the achromatic lens, since it corrects some chromatic aberration. The Huygens–Fresnel principle, a simple model to understand disturbances in wave propagation. Huygens wavelets, the fundamental mathematical basis for scalar diffraction theory

Other[edit]

Huygens Lyceum, High School located in Eindhoven, Netherlands. The Christiaan Huygens, a ship of the Nederland Line. Huygens Scholarship Programme for international students and Dutch students W.I.S.V. Christiaan Huygens: Dutch study guild for the studies Mathematics
Mathematics
and Computer Science
Science
at the Delft University of Technology Huygens Laboratory: Home of the Physics
Physics
department at Leiden University, Netherlands Huygens Supercomputer: National Supercomputer facility of the Netherlands, located at SARA in Amsterdam The Huygens-building in Noordwijk, Netherlands, first building on the Space
Space
Business park opposite Estec (ESA) The Huygens-building at the Radboud University Nijmegen, the Netherlands. One of the major buildings of the science department at the university of Nijmegen. Christiaan Huygensplein, a square in Amsterdam

Works[edit]

Possible depiction of Huygens right of center, detail from L'établissement de l' Académie des Sciences
Académie des Sciences
et fondation de l'observatoire, 1666 by Henri Testelin. Colbert presents the members of the newly founded Académie des Sciences
Académie des Sciences
to king Louis XIV
Louis XIV
of France, around 1675.

1649 – De iis quae liquido supernatant (About the parts above the water, unpublished) 1651 – Cyclometriae 1651 – Theoremata de quadratura hyperboles, ellipsis et circuli, in Oeuvres Complètes, Tome XI, link from Internet Archive. 1654 – De circuli magnitudine inventa 1656 – De Saturni Luna observatio nova (About the new observation of the moon of Saturn
Saturn
– discovery of Titan) 1656 – De motu corporum ex percussione, published only in 1703 1657 – De ratiociniis in ludo aleae = Van reeckening in spelen van geluck (translated by Frans van Schooten) 1659 – Systema saturnium (on the planet Saturn) 1659 – De vi centrifuga (Concerning the centrifugal force), published in 1703 1673 – Horologium oscillatorium sive de motu pendularium (theory and design of the pendulum clock, dedicated to Louis XIV
Louis XIV
of France) 1684 – Astroscopia Compendiaria tubi optici molimine liberata (compound telescopes without a tube) 1685 – Memoriën aengaende het slijpen van glasen tot verrekijckers (How to grind telescope lenses) 1686 – Old Dutch: Kort onderwijs aengaende het gebruijck der horologiën tot het vinden der lenghten van Oost en West (How to use clocks to establish the longitude) 1690 – Traité de la lumière 1690 – Discours de la cause de la pesanteur (Discourse about gravity, from 1669?) 1691 – Lettre touchant le cycle harmonique (Rotterdam, concerning the 31-tone system) 1698 – Cosmotheoros (solar system, cosmology, life in the universe) 1703 – Opuscula posthuma including

De motu corporum ex percussione (Concerning the motions of colliding bodies – contains the first correct laws for collision, dating from 1656). Descriptio automati planetarii (description and design of a planetarium)

1724 – Novus cyclus harmonicus (Leiden, after Huygens' death) 1728 – Christiani Hugenii Zuilichemii, dum viveret Zelhemii toparchae, opuscula posthuma ... (pub. 1728) Alternate title: Opera reliqua, concerning optics and physics 1888–1950 – Huygens, Christiaan. Oeuvres complètes. The Hague Complete work, editors D. Bierens de Haan
D. Bierens de Haan
(tome=deel 1–5), J. Bosscha (6–10), D.J. Korteweg (11–15), A.A. Nijland (15), J.A. Vollgraf (16–22).

Tome I: Correspondance 1638–1656 (1888). Tome II: Correspondance 1657–1659 (1889). Tome III: Correspondance 1660–1661 (1890). Tome IV: Correspondance 1662–1663 (1891). Tome V: Correspondance 1664–1665 (1893). Tome VI: Correspondance 1666–1669 (1895). Tome VII: Correspondance 1670–1675 (1897). Tome VIII: Correspondance 1676–1684 (1899). Tome IX: Correspondance 1685–1690 (1901). Tome X: Correspondance 1691–1695 (1905). Tome XI: Travaux mathématiques 1645–1651 (1908). Tome XII: Travaux mathématiques pures 1652–1656 (1910). Tome XIII, Fasc. I: Dioptrique 1653, 1666 (1916). Tome XIII, Fasc. II: Dioptrique 1685–1692 (1916). Tome XIV: Calcul des probabilités. Travaux de mathématiques pures 1655–1666 (1920). Tome XV: Observations astronomiques. Système de Saturne. Travaux astronomiques 1658–1666 (1925). Tome XVI: Mécanique jusqu’à 1666. Percussion. Question de l'existence et de la perceptibilité du mouvement absolu. Force centrifuge (1929). Tome XVII: L’horloge à pendule de 1651 à 1666. Travaux divers de physique, de mécanique et de technique de 1650 à 1666. Traité des couronnes et des parhélies (1662 ou 1663) (1932). Tome XVIII: L'horloge à pendule ou à balancier de 1666 à 1695. Anecdota (1934). Tome XIX: Mécanique théorique et physique de 1666 à 1695. Huygens à l'Académie royale des sciences (1937). Tome XX: Musique et mathématique. Musique. Mathématiques de 1666 à 1695 (1940). Tome XXI: Cosmologie (1944). Tome XXII: Supplément à la correspondance. Varia. Biographie de Chr. Huygens. Catalogue de la vente des livres de Chr. Huygens (1950).

See also[edit]

History
History
of the internal combustion engine List of largest optical telescopes historically Fokker Organ

Notes[edit]

^ I. Bernard Cohen; George E. Smith (25 April 2002). The Cambridge Companion to Newton. Cambridge University Press. p. 69. ISBN 978-0-521-65696-2. Retrieved 15 May 2013.  ^ Niccolò Guicciardini
Niccolò Guicciardini
(2009). Isaac Newton
Isaac Newton
on mathematical certainty and method. MIT Press. p. 344. ISBN 978-0-262-01317-8. Retrieved 15 May 2013.  ^ "Huygens". Random House Webster's Unabridged Dictionary. ^ Dijksterhuis E.J (1950) De mechanisering van het wereldbeeld. Meulenhoff, Amsterdam. ^ Andriesse, C.D. (2005) Huygens: The Man Behind the Principle. Cambridge University Press. Cambridge: 6 ^ "Christiaan Huygens." Encyclopedia of World Biography. 2004. Encyclopedia.com. (14 December 2012). http://www.encyclopedia.com/doc/1G2-3404703173.html ^ a b http://www.saburchill.com/HOS/astronomy/016.html ^ a b c d e f "Huygens, Christiaan (Also Huyghens, Christian)." Complete Dictionary of Scientific Biography. 2008. Encyclopedia.com. (14 December 2012). http://www.encyclopedia.com/doc/1G2-2830902105.html ^ R. Dugas and P. Costabel, "Chapter Two, The Birth of a new Science" in The Beginnings of Modern Science, edited by Rene Taton, 1958,1964, Basic Books, Inc. ^ Strategic Affection? Gift Exchange in Seventeenth- Century
Century
Holland, by Irma Thoen, pg 127 ^ a b Constantijn Huygens, Lord of Zuilichem (1596–1687), by Adelheid Rech ^ The Heirs Of Archimedes: Science
Science
and the Art Of War Through the Age of Enlightenment, by Brett D. Steele, pg. 20 ^ entoen.nu: Christiaan Huygens
Christiaan Huygens
1629–1695 Science
Science
in the Golden Age ^ Jozef T. Devreese (31 October 2008). 'Magic Is No Magic': The Wonderful World of Simon Stevin. WIT Press. pp. 275–6. ISBN 978-1-84564-391-1. Retrieved 24 April 2013.  ^ H. N. Jahnke (2003). A history of analysis. American Mathematical Soc. p. 47. ISBN 978-0-8218-9050-9. Retrieved 12 May 2013.  ^ Margret Schuchard (2007). Bernhard Varenius: (1622–1650). BRILL. p. 112. ISBN 978-90-04-16363-8. Retrieved 12 May 2013.  ^ a b c d Dictionary, p. 470. ^ Christiaan Huygens
Christiaan Huygens
– A family affair, by Bram Stoffele, pg 80. ^ C. D. Andriesse (25 August 2005). Huygens: The Man Behind the Principle. Cambridge University Press. pp. 80–. ISBN 978-0-521-85090-2. Retrieved 23 April 2013.  ^ C. D. Andriesse (25 August 2005). Huygens: The Man Behind the Principle. Cambridge University Press. pp. 85–6. ISBN 978-0-521-85090-2. Retrieved 10 May 2013.  ^ a b Dictionary, p. 469. ^ Lynn Thorndike (1 March 2003). History
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Thought. Cambridge University Press. pp. 61–2. ISBN 978-0-521-09084-1. Retrieved 24 April 2013.  ^ https://www.houstonpublicmedia.org/articles/shows/engines-of-our-ingenuity/engines-podcast/2017/04/05/194011/engines-of-our-ingenuity-1329-life-in-outer-space-in-1698/ ^ Postmus, Bouwe (1987). "Plokhoy's A way pronouned: Mennonite Utopia or Millennium?". In Dominic Baker-Smith and Cedric Charles Barfoot. Between dream and nature: essays on utopia and dystopia. Amsterdam: Rodopi. pp. 86–8. ISBN 978-90-6203-959-3. Retrieved 24 April 2013. CS1 maint: Uses editors parameter (link) ^ Juliet Cummins; David Burchell (2007). Science, Literature, and Rhetoric
Rhetoric
in Early Modern England. Ashgate Publishing, Ltd. pp. 194–5. ISBN 978-0-7546-5781-1. Retrieved 24 April 2013.  ^ "Johar Huzefa (2009) Nothing But The Facts – Christiaan Huygens". Brighthub.com. 28 September 2009. Retrieved 13 June 2010.  ^ Jacob, Margaret (2010). The Scientific Revolution. Boston: Bedford/St. Martin's. pp. 29, 107–114.  ^ Russell Mccormmach (2012). Weighing the World: The Reverend John Michell of Thornhill. Springer. pp. 129–31. ISBN 978-94-007-2022-0. Retrieved 12 May 2013. 

References[edit]

Bell, A. E. (1947). Christian Huygens and the Development of Science in the Seventeenth Century. Edward Arnold & Co, London.  Daniel Garber (2003). The Cambridge History
History
of Seventeenth-century Philosophy (2 vols.). Cambridge University Press. ISBN 978-0-521-53720-9. Retrieved 11 May 2013.  Alan E. Shapiro (1973) Kinematic Optics: A Study of the Wave
Wave
Theory of Light in the Seventeenth Century, Archive for History
History
of Exact Sciences 11(2/3): 134–266 via Jstor Wiep van Bunge et al. (editors), The Dictionary of Seventeenth and Eighteenth- Century
Century
Dutch Philosophers (2003), Thoemmes Press (two volumes), article Huygens, Christiaan, p. 468–77.

Further reading[edit]

Andriesse, C.D., 2005, Huygens: The Man Behind the Principle. Foreword by Sally Miedema. Cambridge University Press. Boyer, C.B. (1968) A History
History
of Mathematics, New York. Dijksterhuis, E. J. (1961) The Mechanization of the World Picture: Pythagoras to Newton Hooijmaijers, H. (2005) Telling time – Devices for time measurement in Museum Boerhaave
Museum Boerhaave
– A Descriptive Catalogue, Leiden, Museum Boerhaave. Struik, D.J. (1948) A Concise History
History
of Mathematics Van den Ende, H. et al. (2004) Huygens's Legacy, The golden age of the pendulum clock, Fromanteel Ltd, Castle Town, Isle of Man. Yoder, J G. (2005) "Book on the pendulum clock" in Ivor Grattan-Guinness, ed., Landmark Writings in Western Mathematics. Elsevier: 33–45. Christiaan Huygens
Christiaan Huygens
(1629–1695) : Library of Congress Citations. Retrieved 2005-03-30.

External links[edit]

Wikimedia Commons has media related to Christiaan Huygens.

Wikiquote has quotations related to: Christiaan Huygens

Wikisource
Wikisource
has the text of the 1911 Encyclopædia Britannica article Huygens, Christiaan.

Primary sources, translations[edit]

Works by Christiaan Huygens
Christiaan Huygens
at Project Gutenberg:

C. Huygens (translated by Silvanus P. Thompson, 1912), Treatise on Light; Errata.

Works by or about Christiaan Huygens
Christiaan Huygens
at Internet Archive Works by Christiaan Huygens
Christiaan Huygens
at LibriVox
LibriVox
(public domain audiobooks) Correspondence of Christiaan Huygens
Christiaan Huygens
at Early Modern Letters Online De Ratiociniis in Ludo Aleae or The Value of all Chances in Games of Fortune, 1657 Christiaan Huygens' book on probability theory. An English translation published in 1714. Text pdf file. Horologium oscillatorium (German translation, pub. 1913) or Horologium oscillatorium (English translation by Ian Bruce) on the pendulum clock ΚΟΣΜΟΘΕΩΡΟΣ (Cosmotheoros). (English translation of Latin, pub. 1698; subtitled The celestial worlds discover'd: or, Conjectures concerning the inhabitants, plants and productions of the worlds in the planets.) C. Huygens (translated by Silvanus P. Thompson), Traité de la lumière or Treatise on light, London: Macmillan, 1912, archive.org/details/treatiseonlight031310mbp; New York: Dover, 1962; Project Gutenberg, 2005, gutenberg.org/ebooks/14725; Errata Systema Saturnium 1659 text a digital edition of Smithsonian Libraries On Centrifugal Force
Force
(1703) Huygens' work at WorldCat The Correspondence of Christiaan Huygens
Christiaan Huygens
in EMLO Christiaan Huygens
Christiaan Huygens
biography and achievements Portraits of Christiaan Huygens Huygens's books, in digital facsimile from the Linda Hall Library:

(1659) Systema Saturnium (Latin) (1684) Astroscopia compendiaria (Latin) (1690) Traité de la lumiére (French) (1698) ΚΟΣΜΟΘΕΩΡΟΣ, sive De terris cœlestibus (Latin)

Museums[edit]

Huygensmuseum Hofwijck
Hofwijck
in Voorburg, Netherlands, where Huygens lived and worked. Huygens Clocks exhibition from the Science
Science
Museum, London LeidenUniv.nl, Exhibition on Huygens in University Library Leiden
Leiden
(in Dutch)

Other[edit]

O'Connor, John J.; Robertson, Edmund F., "Christiaan Huygens", MacTutor History
History
of Mathematics
Mathematics
archive, University of St Andrews . Huygens and music theory Huygens–Fokker Foundation
Huygens–Fokker Foundation
—on Huygens' 31 equal temperament and how it has been used Christiaan Huygens
Christiaan Huygens
on the 25 Dutch Guilder banknote of the 1950s. Christiaan Huygens
Christiaan Huygens
at the Mathematics
Mathematics
Genealogy Project How to pronounce "Huygens"

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Christiaan Huygens

Books

Systema Saturnium (1659) De Vi Centrifiga (1659) Horologium Oscillatorium (1673) Traité de la Lumiére (1692) Cosmotheoros (1698)

In science and natural philosophy

Centripetal acceleration Coupled oscillation Conception of the standardization of the temperature scale Early history of classical mechanics Early history of calculus Huygens' law Huygens' lemniscate Huygens' principle
Huygens' principle
(Huygens–Fresnel principle) Huygens' construction Huygens' tritone Huygens' wavelet Huygens' wave theory Huygens–Steiner theorem Hypothesis
Hypothesis
of intelligent extraterrestrial life Isochrone curve
Isochrone curve
(tautochrone curve) Foundations of differential geometry of curves (mathematical notions of the evolute and involute of the curve) Scientific foundations of horology Mathematical and physical investigations of properties of the pendulum Modern conception of centrifugal and centripetal forces Music theory
Music theory
of microtones (31 equal temperament) Polarization of light
Polarization of light
(Iceland spar) Rings of Saturn Titan (moon) Theoretical foundations of wave optics (wave theory of light)

In technology

Inventions by Huygens Aerial telescope Cycloidal pendulum Huygens' engine 1 Huygens' eyepiece Magic lantern 2 Spiral balance spring Precision timekeeping
Precision timekeeping
(pendulum clock and spiral-hairspring watch)

Recognitions

List of things named after Christiaan Huygens 2801 Huygens Cassini–Huygens

Huygens probe

Mons Huygens Huygens (crater) Huygens-Fokker Foundation Huygens Gap Huygens Ringlet Horologium (constellation)

Other topics

Cosmos: A Personal Voyage - Episode 6: "Travellers' Tales" (1980 documentary TV series by Carl Sagan) Clocks and Culture, 1300–1700 (1967 history book by Carlo Cipolla) Revolution in Time: Clocks and the Making of the Modern World (1983 history book by David Landes) Scientific Revolution Golden Age of Dutch science and technology Science
Science
and technology in the Dutch Republic Académie des Sciences

Related people

Huygens family Galileo Galilei René Descartes Salomon Coster Antonie van Leeuwenhoek Gottfried Wilhelm Leibniz Isaac Newton Robert Hooke Denis Papin Augustin-Jean Fresnel Thomas Young

1 A rudimentary prototype of internal combustion piston engine. 2 An early practical type of image projector and a precursor to both the modern slide projector and the movie projector.

Wikiquote Wikisource
Wikisource
texts

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Inner large (with trojans)

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Telesto Calypso

Dione

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Outer large

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Norse group

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Gallic group

Albiorix Bebhionn Erriapus Tarvos

Rings of Saturn Cassini–Huygens Themis Chiron S/2004 S 6 S/2004 S 4 S/2004 S 3 In fiction

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Titan

General

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Lists

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Lakes and seas

Seas

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Lakes

Abaya Lacus Bolsena Lacus Feia Lacus Hammar Lacus Jingpo Lacus Kivu Lacus Koitere Lacus Ladoga Lacus Mackay Lacus Müggel Lacus Neagh Lacus Ontario Lacus Sotonera Lacus Albano Lacus

Rivers

Vid Flumina

Dry lakes

Eyre Lacuna Ngami Lacuna Woytchugga Lacuna

Features

Adiri Arrakis Planitia Dilmun Doom Mons Erebor Mons Ganesa Macula Guabonito Irensaga Montes Mayda Insula Menrva Mezzoramia Mindolluin Montes Misty Montes Mithrim Montes Perkunas Virgae Shangri-La Shikoku Facula Sotra Patera Taniquetil Montes Tsegihi Tui Regio Xanadu

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Cassini–Huygens

Huygens

Proposed

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Enceladus
and Titan Journey to Enceladus
Enceladus
and Titan TALISE Titan Mare Explorer Titan Saturn
Saturn
System Mission Oceanus

See also

Colonization of Titan

Other topics

Memorials on Titan Titan in fiction

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Spacecraft missions to Saturn

Orbiters

Cassini–Huygens

timeline retirement

Landers

Huygens (Titan)

Flybys

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Proposed missions

AVIATR Dragonfly Enceladus
Enceladus
Life Finder ( Enceladus
Enceladus
only) Enceladus
Enceladus
Explorer ( Enceladus
Enceladus
only) Explorer of Enceladus
Enceladus
and Titan Journey to Enceladus
Enceladus
and Titan Kronos Life Investigation For Enceladus
Enceladus
( Enceladus
Enceladus
only) Oceanus (Titan only) Saturn
Saturn
Atmospheric Entry Probe Saturn
Saturn
Ring Observer SPRITE TALISE (Titan only) Titan Mare Explorer
Titan Mare Explorer
(Titan only) Titan Saturn
Saturn
System Mission

Former plans

Soviet mission plan

There are no ongoing missions to Saturn

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Extraterrestrial life

Events and objects

ALH84001 Cells in the stratosphere CI1 fossils Murchison meteorite Nakhla meteorite Polonnaruwa meteorite Red rain in Kerala Shergotty meteorite Viking lander biological experiments Yamato 000593

Signals of interest

CP 1919 (misidentified pulsar) CTA-102 (misidentified quasar) Fast radio burst (unknown origin) Wow! signal
Wow! signal
(inconclusive) KIC 8462852
KIC 8462852
(unusual light fluctuations) SHGb02+14a (radio source) HD 164595
HD 164595
signal (unknown origin)

Life in the Universe

Earliest known life forms Life on Enceladus Life on Europa Life on Mars Life on Titan Life on Venus

Planetary habitability

Catalog of Nearby Habitable Systems Circumstellar habitable zone Earth analog Extraterrestrial liquid water Galactic habitable zone Habitability of binary star systems Habitability of orange dwarf systems Habitability of red dwarf systems Natural satellite habitability Planetary habitability

Space
Space
missions

Beagle 2 Biological Oxidant and Life Detection BioSentinel Curiosity Darwin Enceladus
Enceladus
Explorer Enceladus
Enceladus
Life Finder Europa Clipper ExoMars ExoLance EXPOSE Foton-M3 Icebreaker Life Journey to Enceladus
Enceladus
and Titan Laplace-P Life Investigation For Enceladus Living Interplanetary Flight Experiment Mars
Mars
Geyser Hopper Mars
Mars
sample return mission Mars
Mars
2020 Northern Light Opportunity SpaceX Red Dragon Spirit Tanpopo Titan Mare Explorer Venus In Situ Explorer Viking 1 Viking 2

Interstellar communication

Active SETI Allen Telescope
Telescope
Array Arecibo message Arecibo Observatory Berkeley SETI Research Center Bracewell probe Breakthrough Initiatives

Breakthrough Listen Breakthrough Message

Communication with extraterrestrial intelligence Gauss's Pythagorean right triangle proposal Lincos language NIROSETI Pioneer plaque Project Cyclops Project Ozma Project Phoenix SERENDIP Search for extraterrestrial intelligence SETI@home setiQuest Voyager Golden Record Water hole Xenolinguistics

Exhibitions

The Science
Science
of Aliens

Hypotheses

Ancient astronauts Aestivation hypothesis Aurelia and Blue Moon Cosmic pluralism Directed panspermia Drake equation Extraterrestrial hypothesis Fermi paradox Great Filter Hypothetical types of biochemistry Interplanetary contamination Kardashev scale Mediocrity principle Neocatastrophism Panspermia Planetarium
Planetarium
hypothesis Rare Earth hypothesis Zoo hypothesis

Related topics

Astrobiology Astroecology Biosignature Rejection of Earth-based abiogenesis (Fred Hoyle) Brookings Report Planetary protection Potential cultural impact of extraterrestrial contact Exotheology Extraterrestrials in fiction Extremophile Nexus for Exoplanet System Science Noogenesis San Marino Scale Technosignature UFO religion Xenoarchaeology

v t e

Time

Key concepts

Past

history deep time

Present Future Futures studies Far future in religion Far future in science fiction and popular culture Timeline
Timeline
of the far future Eternity Eternity
Eternity
of the world

Measurement and standards

Chronometry

UTC UT TAI Unit of time Planck time Second Minute Hour Day Week Month Season Year Decade Century Millennium Tropical year Sidereal year Samvatsara

Measurement systems

Time
Time
zone Six-hour clock 12-hour clock 24-hour clock Daylight saving time Solar time Sidereal time Metric time Decimal time Hexadecimal time

Calendars

Gregorian Julian Hebrew Islamic Lunar Solar Hijri Mayan Intercalation Leap second Leap year

Clocks

Horology History
History
of timekeeping devices Main types

astrarium atomic

quantum

marine sundial sundial markup schema watch water-based

Chronology History

Astronomical chronology Big History Calendar
Calendar
era Chronicle Deep time Periodization Regnal year Timeline

Religion Mythology

Dreamtime Kāla Kalachakra Prophecy Time
Time
and fate deities Wheel of time Immortality

Philosophy of time

A-series and B-series B-theory of time Causality Duration Endurantism Eternal return Eternalism Event Multiple time dimensions Perdurantism Presentism Static interpretation of time Temporal finitism Temporal parts The Unreality of Time

Human experience and use of time

Accounting period Chronemics Fiscal year Generation time Mental chronometry Music Procrastination Punctuality Temporal database Term Time
Time
discipline Time
Time
management Time
Time
perception

Specious present

Time-tracking software Time-use research Time-based currency
Time-based currency
(time banking) Time
Time
value of money Time
Time
clock Timesheet Yesterday – Today – Tomorrow

Time
Time
in

Geology

Geological time

age chron eon epoch era period

Geochronology Geological history of Earth

Physics

Absolute time and space Arrow of time Chronon Coordinate time Imaginary time Planck epoch Planck time Proper time Rate Spacetime Theory of relativity Time
Time
dilation

gravitational

Time
Time
domain Time
Time
translation symmetry Time
Time
reversal symmetry

other subject areas

Chronological dating Chronobiology Circadian rhythms Dating methodologies in archaeology Time
Time
geography

Related topics

Carpe diem Clock
Clock
position Space System time Tempus fugit Time
Time
capsule Time
Time
complexity Time
Time
signature Time
Time
travel

Time
Time
portal Category

v t e

Time
Time
measurement and standards

Chronometry Orders of magnitude Metrology

International standards

Coordinated Universal Time

offset

UT ΔT DUT1 International Earth Rotation and Reference Systems Service ISO 31-1 ISO 8601 International Atomic Time 6-hour clock 12-hour clock 24-hour clock Barycentric Coordinate Time Barycentric Dynamical Time Civil time Daylight saving time Geocentric Coordinate Time International Date Line Leap second Solar time Terrestrial Time Time
Time
zone 180th meridian

Obsolete standards

Ephemeris time Greenwich Mean Time Prime meridian

Time
Time
in physics

Absolute time and space Spacetime Chronon Continuous signal Coordinate time Cosmological decade Discrete time and continuous time Planck time Proper time Theory of relativity Time
Time
dilation Gravitational time dilation Time
Time
domain Time
Time
translation symmetry T-symmetry

Horology

Clock Astrarium Atomic clock Complication History
History
of timekeeping devices Hourglass Marine chronometer Marine sandglass Radio clock Watch Water clock Sundial Dialing scales Equation of time History
History
of sundials Sundial
Sundial
markup schema

Calendar

Astronomical Dominical letter Epact Equinox Gregorian Hebrew Hindu Intercalation Islamic Julian Leap year Lunar Lunisolar Solar Solstice Tropical year Weekday determination Weekday names

Archaeology and geology

Chronological dating Geologic time scale International Commission on Stratigraphy

Astronomical chronology

Galactic year Nuclear timescale Precession Sidereal time

Other units of time

Flick Shake Jiffy Second Minute Moment Hour Day Week Fortnight Month Year Olympiad Lustrum Decade Century Saeculum Millennium

Related topics

Chronology Duration

music

Mental chronometry Metric time System time Time
Time
value of money Timekeeper

v t e

Microtonal music

Composers

Easley Blackwood Jr. Heinz Bohlen Wendy Carlos Julián Carrillo Mildred Couper John Eaton Alois Hába Lou Harrison Christiaan Huygens Charles Ives Ben Johnston Joel Mandelbaum Joe Maneri John Schneider Ezra Sims Nicola Vicentino Elaine Walker Ivan Wyschnegradsky

Inventors of microtonal instruments

Glenn Branca Ivor Darreg Adriaan Fokker Yuri Landman Harry Partch

Tunings and scales

Non-octave- repeating scales

Alpha scale Beta scale Gamma scale Delta scale Lambda scale (Bohlen–Pierce scale)

Equal temperament

15 17 19 22 24 31 34 41 53 58 72

Just intonation

Harry Partch's 43-tone scale Triple diatonic

Concepts and techniques

Limit Otonality and Utonality Semitone Sonido 13 Xenharmonicity

Groups and publications

Boston Microtonal Society Genesis of a Music Huygens-Fokker Foundation Tonalsoft Xenharmonic Bulletin

Compositions

Beauty in the Beast quarter tone pieces just pieces Mother Sonata for Microtonal Piano Suite for Microtonal Piano Twelve Microtonal Etudes for Electronic Music Media

Other topics

Enharmonic keyboard Generalized keyboard Modernism (music)

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The Age of Enlightenment

Topics

Atheism Capitalism Civil liberties Counter-Enlightenment Critical thinking Deism Democracy Empiricism Encyclopédistes Enlightened absolutism Free markets Haskalah Humanism Human rights Liberalism Liberté, égalité, fraternité Methodological skepticism Nationalism Natural philosophy Objectivity Rationality Rationalism Reason Reductionism Sapere aude Science Scientific method Socialism Universality Weimar Classicism

Thinkers

France

Jean le Rond d'Alembert Étienne Bonnot de Condillac Marquis de Condorcet Denis Diderot Claude Adrien Helvétius Baron d'Holbach Georges-Louis Leclerc Montesquieu François Quesnay Jean-Jacques Rousseau Marquis de Sade Voltaire

Germany

Johann Wolfgang von Goethe Johann Georg Hamann Johann Gottfried von Herder Friedrich Heinrich Jacobi Immanuel Kant Gotthold Ephraim Lessing Moses Mendelssohn Friedrich Schiller Thomas Wizenmann

Greece

Neophytos Doukas Theoklitos Farmakidis Rigas Feraios Theophilos Kairis Adamantios Korais

Ireland

Robert Boyle Edmund Burke

Italy

Cesare Beccaria Gaetano Filangieri Antonio Genovesi Pietro Verri

The Netherlands

Spinoza Hugo Grotius Balthasar Bekker Bernard Nieuwentyt Frederik van Leenhof Christiaan Huygens Antonie van Leeuwenhoek Jan Swammerdam

Poland

Tadeusz Czacki Hugo Kołłątaj Stanisław Konarski Ignacy Krasicki Julian Ursyn Niemcewicz Stanisław August Poniatowski Jędrzej Śniadecki Stanisław Staszic Józef Wybicki Andrzej Stanisław Załuski Józef Andrzej Załuski

Portugal

Sebastião José de Carvalho e Melo

Russia

Catherine II

Spain

Charles III Benito Jerónimo Feijóo y Montenegro

United Kingdom (Scotland)

Francis Bacon Jeremy Bentham Joseph Black James Boswell Adam Ferguson Edward Gibbon Robert Hooke David Hume Francis Hutcheson Samuel Johnson John Locke Isaac Newton Thomas Reid Adam Smith Mary Wollstonecraft

United States

Benjamin Franklin Thomas Jefferson James Madison George Mason Thomas Paine

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WorldCat Identities VIAF: 9894043 LCCN: n79134100 ISNI: 0000 0001 0868 7618 GND: 118639749 SELIBR: 250110 SUDOC: 030533023 BNF: cb12192922r (data) BPN: 19453564 BIBSYS: 90379757 ULAN: 500026922 MGP: 125561 NLA: 35216514 NDL: 00468723 BNE: XX949106 RKD: 40

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