Coordinates	12°2′36″N77°1′42″N
name	Tycho Ottesen Brahe
birth date	14 December 1546
birth place	Knutstorp Castle, Scania
death date	24 October 1601 (aged 54)
death place	Prague
education	Private
occupation	Nobleman, Astronomer
fields	Astronomy, Cosmology
religion	Lutheran
spouse	Kirstine Barbara Jørgensdatter
parents	Otte Brahe and Beate Bille
children	8
nationality	Danish
signature	Tycho Brahe Signature.svg }}

Tycho Brahe () (14 December 1546 – 24 October 1601), born Tyge Ottesen Brahe, was a Danish nobleman known for his accurate and comprehensive astronomical and planetary observations. Coming from Scania, then part of Denmark, now part of modern-day Sweden, Tycho was well known in his lifetime as an astronomer and alchemist.

In his ''De nova stella'' (On the new star) of 1573, he refuted the theory of the celestial spheres by showing the celestial heavens were not in an immutable or unchanging state of perfection as previously assumed by Aristotle and Ptolemy. His precise measurements indicated that "new stars" (novae or also now known as supernovae), in particular that of 1572, lacked the parallax expected in sub-lunar phenomena, and were therefore not "atmospheric" tail-less comets as previously believed, but occurred above the atmosphere and moon. Using similar measurements he showed that comets were also not atmospheric phenomena, as previously thought, and must pass through the supposed "immutable" celestial spheres.

Tycho Brahe was granted an estate on the island of Hven and the funding to build the Uraniborg, an early research institute, where he built large astronomical instruments and took many careful measurements, and later Stjerneborg, underground, when he discovered that his instruments in the former were not sufficiently steady. Something of an autocrat on the island he nevertheless founded manufactories such as paper-making to provide material for printing his results. Something akin to a research institute was founded which John Napier attended. After disagreements with the new Danish king in 1597, he was invited by the Bohemian king and Holy Roman emperor Rudolph II to Prague, where he became the official imperial astronomer. He built the new observatory at Benátky nad Jizerou. Here, from 1600 until his death in 1601, he was assisted by Johannes Kepler. Kepler later used Tycho's astronomical results to develop his own theories of astronomy.

As an astronomer, Tycho worked to combine what he saw as the geometrical benefits of the Copernican system with the philosophical benefits of the Ptolemaic system into his own model of the universe, the Tychonic system. Furthermore, he was the last of the major naked eye astronomers, working without telescopes for his observations.

Tycho is credited with the most accurate astronomical observations of his time, and the data were used by his assistant, Johannes Kepler, to derive the laws of planetary motion. No one before Tycho had attempted to make so many planetary observations.

Life

Early years

Tycho was born at his family's ancestral seat of Knutstorp Castle (Danish: ''Knudstrup borg''; Swedish: ''Knutstorps borg''), about eight kilometres north of Svalöv in then Danish Scania, now Swedish, to Otte Brahe and Beate Bille. His twin brother died before being baptized. Tycho wrote a Latin ode to his dead twin, which was printed in 1572 as his first published work. He also had two sisters, one older (Kirstine Brahe) and one younger (Sophia Brahe).

Otte Brahe, Tycho's father, was a nobleman and an important figure at the court of the Danish king. His mother, Beate Bille, came from an important family that had produced leading churchmen and politicians. Both parents are buried under the floor of Kågeröd Church, four kilometres east of Knutstorp. An epitaph, originally from Knutstorp, but now on a plaque near the church door, shows the whole family, including Tycho as a boy.

Tycho later wrote that when he was around age two, his uncle, Danish nobleman Jørgen Thygesen Brahe, "without the knowledge of my parents took me away with him while I was in my earliest youth to become a scholar". Apparently, this did not lead to dispute, nor did his parents attempt to get him back. According to one source, Tycho's parents had promised to hand over a boy child to Jørgen and his wife, who were childless, but had not honoured this promise. Jørgen seems to have taken matters into his own hands and took the child away to his own residence, Tosterup Castle. Jørgen Brahe inherited considerable wealth from his parents, which in terms of the social structure of the time made him eligible for a royal appointment as county sheriff. He was successively sheriff to Tranekjær (1542–49), Odensegaard (1549–52), Vordingborg Castle (1552–57), and finally (1555 until his death in 1565) to Queen Dorothea at Nykøbing Castle on Falster.

Tycho attended Latin school from ages 6 to 12, but the name of the school is not known. At age 12, on 19 April 1559, Tycho began studies at the University of Copenhagen. There, following his uncle's wishes, he studied law, but also studied a variety of other subjects and became interested in astronomy. The solar eclipse of 21 August 1560, especially the fact that it had been predicted, so impressed him that he began to make his own studies of astronomy, helped by some of the professors. He purchased an ephemeris and books on astronomy, including Johannes de Sacrobosco's ''De sphaera mundi'', Petrus Apianus's ''Cosmographia seu descriptio totius orbis'' and Regiomontanus's ''De triangulis omnimodis''. Jørgen Thygesen Brahe, however, wanted Tycho to educate himself in order to become a civil servant, and sent him on a study tour of Europe in early 1562. Tycho was given the young Anders Sørensen Vedel as mentor, whom he eventually talked into allowing the pursuit of astronomy during the tour. At age 17, Tycho wrote:

I've studied all available charts of the planets and stars and none of them match the others. There are just as many measurements and methods as there are astronomers and all of them disagree. What's needed is a long term project with the aim of mapping the heavens conducted from a single location over a period of several years.

Tycho realized that progress in astronomy required systematic, rigorous observation, night after night, using the most accurate instruments obtainable. This program became his life's work. Tycho improved and enlarged existing instruments, and built entirely new ones. His sister Sophia assisted Tycho in many of his measurements. Tycho was the last major astronomer to work without the aid of a telescope, soon to be turned skyward by Galileo and others.

Tycho jealously guarded his large body of celestial measurements, which Kepler "usurped" following Tycho's death.

Tycho's nose

While studying at University of Rostock in Germany, on 29 December 1566 Tycho lost part of his nose in a duel against fellow Danish nobleman Manderup Parsbjerg. Tycho had earlier quarrelled with Parsbjerg at a wedding dance at professor Lucas Bacmeister's house on the 10th, and again on the 27th. The duel two days later (in the dark) resulted in Tycho losing the bridge of his nose. From this event Tycho became interested in medicine and alchemy. For the rest of his life, he was said to have worn a replacement made of silver and gold, using a paste to keep it attached. Some people, such as Fredric Ihren and Cecil Adams have suggested that the false nose also had copper. Ihren wrote that when Tycho's tomb was opened in 24 June 1901 green marks were found on his skull, suggesting copper. Cecil Adams also mentions a green colouring and that medical experts examined the remains. Some historians have speculated that he wore a number of different prosthetics for different occasions, noting that a copper nose would have been more comfortable and less heavy than a precious metal one.

Death of his uncle

His uncle and foster father, Jørgen Brahe, died in 1565 of pneumonia after rescuing Frederick II of Denmark from drowning. In April 1567, Tycho returned home from his travels and his father wanted him to take up law, but Tycho was allowed to make trips to Rostock, then on to Augsburg (where he built a great quadrant), Basel, and Freiburg. At the end of 1570 he was informed about his father's ill health, so he returned to Knutstorp Castle, where his father died on 9 May 1571. Soon after, his other uncle, Steen Bille, helped him build an observatory and alchemical laboratory at Herrevad Abbey.

Family life

Towards the end of 1571, Tycho fell in love with Kirsten, daughter of Jørgen Hansen, the Lutheran minister in Knudstrup. She was a commoner, and Tycho never formally married her. However, under Danish law, when a nobleman and a common woman lived together openly as husband and wife, and she wore the keys to the household at her belt like any true wife, their alliance became a binding morganatic marriage after three years. The husband retained his noble status and privileges; the wife remained a commoner. Their children were legitimate in the eyes of the law, but they were commoners like their mother and could not inherit their father's name, coat of arms, or landholdings.

Kirsten Jørgensdatter gave birth to their first daughter, Kirstine (named after Tycho's late sister, who died at 13) on 12 October 1573. Together they had eight children, six of whom lived to adulthood. In 1574, they moved to Copenhagen where their daughter Magdalene was born. Kirsten and Tycho lived together for almost thirty years until Tycho's death.

Tycho's Elk (Moose)

Tycho was said to own one percent of the entire wealth of Denmark at one point in the 1580s and he often held large social gatherings in his castle. He kept a dwarf named Jepp (whom Tycho believed to be clairvoyant) as a court jester who sat under the table during dinner. Pierre Gassendi wrote that Tycho also had a tame elk (moose) and that his mentor the Landgrave Wilhelm of Hesse-Kassel (Hesse-Cassel) asked whether there was an animal faster than a deer. Tycho replied, writing that there was none, but he could send his tame elk. When Wilhelm replied he would accept one in exchange for a horse, Tycho replied with the sad news that the elk had just died on a visit to entertain a nobleman at Landskrona. Apparently during dinner the elk had drunk a lot of beer, fallen down the stairs, and died.

Death

Tycho suddenly contracted a bladder or kidney ailment after attending a banquet in Prague, and died eleven days later, on 24 October 1601. According to Kepler's first hand account, Tycho had refused to leave the banquet to relieve himself because it would have been a breach of etiquette. After he had returned home he was no longer able to urinate, except, eventually, in very small quantities and with excruciating pain. The night before he died he suffered from a delirium during which he was frequently heard to exclaim that he hoped he would not seem to have lived in vain. Before dying, he urged Kepler to finish the ''Rudolphine Tables'' and expressed the hope that he would do so by adopting Tycho's own planetary system, rather than that of Copernicus. A contemporary physician attributed his death to a kidney stone, but no kidney stones were found during an autopsy performed after his body was exhumed in 1901, and the 20th century medical assessment is that it is more likely to have resulted from uremia.

Recent investigations have suggested that Tycho did not die from urinary problems but instead from mercury poisoning—extremely toxic levels of it have been found in hairs from his moustache. The results were, however, not conclusive. Prague City Hall approved a request by Danish scientists to exhume the remains in February 2010, and a team of Czech and Danish scientists from Aarhus University arrived in November 2010, to take bone, hair and clothing samples for analysis.

Tycho's body is currently interred in a tomb in the Church of Our Lady in front of Týn, in Old Town Square near the Prague Astronomical Clock.

Career: observing the heavens

The 1572 supernova

On 11 November 1572, Tycho observed (from Herrevad Abbey) a very bright star, now named SN 1572, which had unexpectedly appeared in the constellation Cassiopeia. Because it had been maintained since antiquity that the world beyond the Moon's orbit was eternally unchangeable (celestial immutability was a fundamental axiom of the Aristotelian world-view), other observers held that the phenomenon was something in the terrestrial sphere below the Moon. However, in the first instance Tycho observed that the object showed no daily parallax against the background of the fixed stars. This implied it was at least farther away than the Moon and those planets that do show such parallax. He also found the object did not change its position relative to the fixed stars over several months as all planets did in their periodic orbital motions, even the outer planets for which no daily parallax was detectable. This suggested it was not even a planet, but a fixed star in the stellar sphere beyond all the planets. In 1573 he published a small book, ''De nova stella'' thereby coining the term nova for a "new" star (we now classify this star as a supernova and we know that it is 7500 light-years from Earth). This discovery was decisive for his choice of astronomy as a profession. Tycho was strongly critical of those who dismissed the implications of the astronomical appearance, writing in the preface to ''De nova stella'': "O crassa ingenia. O caecos coeli spectatores" ("Oh thick wits. Oh blind watchers of the sky").

Tycho's discovery was the inspiration for Edgar Allan Poe's poem, "Al Aaraaf". In 1998, ''Sky & Telescope'' magazine published an article by Donald W. Olson, Marilynn S. Olson and Russell L. Doescher arguing, in part, that Tycho's supernova was also the same "star that's westward from the pole" in Shakespeare's ''Hamlet''.

Tycho's observatories

In 1574, Tycho published the observations made in 1572 from his first observatory at Herrevad Abbey. He then started lecturing on astronomy, but gave it up and left Denmark in spring 1575 to tour abroad. He first visited William IV, Landgrave of Hesse-Kassel's observatory at Kassel, then went on to Frankfurt, Basel and Venice. Upon his return he intended to relocate to Basel, but King Frederick II of Denmark, desiring to keep the distinguished scientist, offered Tycho the island of Hven in Oresund and funding to set up an observatory. Purportedly, Tycho and King Frederick II of Denmark shared a very close relationship, rumored to be homosexual in nature, which later aggravated relations with Frederick's son Christian IV. Tycho first built Uraniborg in 1576 (with a laboratory for his alchemical experiments in its cellar) and then Stjerneborg in 1581. Unusual for the time, Tycho established Uraniborg as a research centre, where almost 100 students and artisans worked from 1576 to 1597.

After Frederick died in 1588 and his 11-year-old son, Christian IV, succeeded him, Tycho's influence steadily declined. After several unpleasant disagreements, Tycho left Hven in 1597.

He moved to Prague in 1599. Sponsored by Rudolf II, Holy Roman Emperor, Tycho built a new observatory in a castle in Benátky nad Jizerou, 50 km from Prague, and worked there for one year. The emperor then brought him back to Prague, where he stayed until his death. Tycho received financial support from several nobles in addition to the emperor, including Oldrich Desiderius Pruskowsky von Pruskow, to whom he dedicated his famous "Mechanica". In return for their support, Tycho's duties included preparing astrological charts and predictions for his patrons on events such as births, weather forecasting, and astrological interpretations of significant astronomical events, such as the supernova of 1572 (sometimes called Tycho's supernova) and the Great Comet of 1577.

Tycho's observational astronomy

Tycho's observations of stellar and planetary positions were noteworthy both for their accuracy and quantity. His celestial positions were much more accurate than those of any predecessor or contemporary. Rawlins (1993, §B2) asserts of Tycho's Star Catalog D, "In it, Tycho achieved, on a mass scale, a precision far beyond that of earlier catalogers. Cat D represents an unprecedented confluence of skills: instrumental, observational, & computational—all of which combined to enable Tycho to place most of his hundreds of recorded stars to an accuracy of ordermag 1'!"

He aspired to a level of accuracy in his estimated positions of celestial bodies of being consistently within 1 arcminute of their real celestial locations, and also claimed to have achieved this level. But in fact many of the stellar positions in his star catalogues were less accurate than that. The median errors for the stellar positions in his final published catalog were about 1'.5, indicating that only half of the entries were more accurate than that, with an overall mean error in each coordinate of around 2'. Although the stellar observations as recorded in his observational logs were more accurate, varying from 32.3" to 48.8" for different instruments, systematic errors of as much as 3' were introduced into some of the stellar positions Tycho published in his star catalog - due for instance, to his application of an erroneous ancient value of parallax and his neglect of polestar refraction. Incorrect transcription in the final published star catalogue, by scribes in Brahe's employ, was the source of even larger errors, sometimes by many degrees.

After his death, his records of the motion of the planet Mars provided evidence to support Kepler's discovery of the ellipse and area laws of planetary motion. Kepler's application of these two laws to obtain astronomical tables of unprecedented accuracy (the ''Rudolphine Tables'') provided powerful support for his heliocentric model of the solar system.

Tycho himself was not a Copernican, but proposed a system in which the Sun and Moon orbited the Earth, while the other planets orbited the Sun. His system provided a safe position for astronomers who were dissatisfied with older models but were reluctant to accept the Earth's motion. It gained a considerable following after 1616 when Rome decided officially that the heliocentric model was contrary to both philosophy and Scripture, and could be discussed only as a computational convenience that had no connection to fact. His system also offered a major innovation: while both the geocentric model and the heliocentric model as set forth by Copernicus relied on the idea of transparent rotating crystalline spheres to carry the planets in their orbits, Tycho eliminated the spheres entirely.

Celestial objects observed near the horizon and above appear with a greater altitude than the real one, due to atmospheric refraction, and one of Tycho's most important innovations was that he worked out and published the very first tables for the systematic correction of this possible source of error. But as advanced as they were, they attributed no refraction whatever above 45 degrees altitude for solar refraction, and none for starlight above 20 degrees altitude.

To perform the huge number of multiplications needed to produce much of his astronomical data, Tycho relied heavily on the then-new technique of ''prosthaphaeresis'', an algorithm for approximating products based on trigonometric identities that predated logarithms.

Tycho's geo-heliocentric astronomy

Kepler tried, but was unable, to persuade Tycho to adopt the heliocentric model of the solar system. Tycho believed in geocentrism because he held the Earth was just too sluggish to be continuously in motion and also believed that if the Earth orbited the Sun annually there should be an observable stellar parallax over any period of six months, during which the angular orientation of a given star would change. This parallax does exist, but is so small it was not detected until the 1830s, when Friedrich Bessel discovered a stellar parallax of 0.314 arcseconds of the star 61 Cygni in 1838. Tycho advocated an alternative to the Ptolemaic geocentric system, a geo-heliocentric system now known as the Tychonic system. In such a system, the Sun annually circles a central Earth (regarded as essentially different from the planets), while the five planets orbit the Sun.

Tycho was not the first to propose a geoheliocentric system. It used to be thought that Heraclides in the 4th century BC had suggested that Mercury and Venus revolve around the Sun, which in turn (along with the other planets) revolves around the Earth. Ambrosius Theodosius Macrobius (395–423 AD) later described this as the "Egyptian System," stating that "it did not escape the skill of the Egyptians," though there is no other evidence it was known in ancient Egypt. The difference was that Tycho's system had all the planets (with the exception of Earth) revolving around the Sun, instead of just the interior planets of Mercury and Venus. In this regard, he was anticipated in the 15th century by the Kerala school astronomer Nilakantha Somayaji, whose geoheliocentric system also had all the planets revolving around the Sun. The difference to both these systems was that Tycho's model of the Earth does not rotate daily, as Heraclides and Nilakantha claimed, but is static.

Another crucial difference between Tycho's 1587 geo-heliocentric model and those of other geo-heliocentric astronomers, such as Paul Wittich, Reimarus Ursus, Helisaeus Roeslin and David Origanus, was that the orbits of Mars and the Sun intersected. This was because Tycho had come to believe the distance of Mars from the Earth at opposition (that is, when Mars is on the opposite side of the sky from the Sun) was less than that of the Sun from the Earth. Tycho believed this because he came to believe Mars had a greater daily parallax than the Sun. But in 1584 in a letter to a fellow astronomer, Brucaeus, he had claimed that Mars had been further than the Sun at the opposition of 1582, because he had observed that Mars had little or no daily parallax. He said he had therefore rejected Copernicus's model because it predicted Mars would be at only two-thirds the distance of the Sun. But he apparently later changed his mind to the opinion that Mars at opposition was indeed nearer the Earth than the Sun was, but apparently without any valid observational evidence in any discernible Martian parallax. Such intersecting Martian and solar orbits meant that there could be no solid rotating celestial spheres, because they could not possibly interpenetrate. Arguably this conclusion was independently supported by the conclusion that the comet of 1577 was superlunary, because it showed less daily parallax than the Moon and thus must pass through any celestial spheres in its transit.

Tychonic astronomy after Tycho

Galileo's 1610 telescopic discovery that Venus shows a full set of phases refuted the pure geocentric Ptolemaic model. After that it seems 17th century astronomy then mostly converted to geo-heliocentric planetary models that could explain these phases just as well as the heliocentric model could, but without the latter's disadvantage of the failure to detect any annual stellar parallax that Tycho and others regarded as refuting it. The three main geo-heliocentric models were the Tychonic, the Capellan with just Mercury and Venus orbiting the Sun such as favoured by Francis Bacon, for example, and the extended Capellan model of Riccioli with Mars also orbiting the Sun whilst Saturn and Jupiter orbit the fixed Earth. But the Tychonic model was probably the most popular, albeit probably in what was known as 'the semi-Tychonic' version with a daily rotating Earth. This model was advocated by Tycho's ex-assistant and disciple Longomontanus in his 1622 ''Astronomia Danica'' that was the intended completion of Tycho's planetary model with his observational data, and which was regarded as the canonical statement of the complete Tychonic planetary system.

A conversion of astronomers to geo-rotational geo-heliocentric models with a daily rotating Earth such as that of Longomontanus may have been precipitated by Francesco Sizzi's 1613 discovery of annually periodic seasonal variations of sunspot trajectories across the sun's disc. They appear to oscillate above and below its apparent equator over the course of the four seasons. This seasonal variation is explained much better by the hypothesis of a daily rotating Earth together with that of the sun's axis being tilted throughout its supposed annual orbit than by that of a daily orbiting sun, if not even refuting the latter hypothesis because it predicts a daily vertical oscillation of a sunspot's position, contrary to observation. This discovery and its import for heliocentrism, but not for geo-heliocentrism, is discussed in the Third Day of Galileo's 1632 ''Dialogo''. However, prior to that discovery, in the late 16th century the geo-heliocentric models of Ursus and Roslin had featured a daily rotating Earth, unlike Tycho's geo-static model, as indeed had that of Heraclides in antiquity, for whatever reason.

The fact that Longomontanus's book was republished in two later editions in 1640 and 1663 no doubt reflected the popularity of Tychonic astronomy in the 17th century. Its adherents included John Donne and the atomist and astronomer Pierre Gassendi.

The ardent anti-heliocentric French astronomer Jean-Baptiste Morin devised a Tychonic planetary model with elliptical orbits published in 1650 in a simplified, Tychonic version of the ''Rudolphine Tables''. Some acceptance of the Tychonic system persisted through the 17th century and in places until the early 18th century; it was supported (after a 1633 decree about the Copernican controversy) by "a flood of pro-Tycho literature" of Jesuit origin. Among pro-Tycho Jesuits, Ignace Pardies declared in 1691 that it was still the commonly accepted system, and Francesco Blanchinus reiterated that as late as 1728. Persistence of the Tychonic system, especially in Catholic countries, has been attributed to its satisfaction of a need (relative to Catholic doctrine) for "a safe synthesis of ancient and modern". After 1670, even many Jesuit writers only thinly disguised their Copernicanism. But in Germany, Holland, and England, the Tychonic system "vanished from the literature much earlier".

James Bradley's discovery of stellar aberration, published 1729, eventually gave direct evidence excluding the possibility of all forms of geocentrism including Tycho's. Stellar aberration could only be satisfactorily explained on the basis that the Earth is in annual orbit around the Sun, with an orbital velocity that combines with the finite speed of the light coming from an observed star or planet, to affect the apparent direction of the body observed.

Tycho's lunar theory

Tycho's distinctive contributions to lunar theory include his discovery of the variation of the Moon's longitude. This represents the largest inequality of longitude after the equation of the center and the evection. He also discovered librations in the inclination of the plane of the lunar orbit, relative to the ecliptic (which is not a constant of about 5° as had been believed before him, but fluctuates through a range of over a quarter of a degree), and accompanying oscillations in the longitude of the lunar node. These represent perturbations in the Moon's ecliptic latitude. Tycho's lunar theory doubled the number of distinct lunar inequalities, relative to those anciently known, and reduced the discrepancies of lunar theory to about 1/5 of their previous amounts. It was published posthumously by Kepler in 1602, and Kepler's own derivative form appears in Kepler's Rudolphine Tables of 1627.

Legacy

Although Tycho's planetary model was soon discredited, his astronomical observations were an essential contribution to the scientific revolution. The traditional view of Tycho is that he was primarily an empiricist who set new standards for precise and objective measurements. This appraisal originated in Pierre Gassendi's 1654 biography, ''Tychonis Brahe, equitis Dani, astronomorum coryphaei, vita''. It was furthered by Johann Dreyer's biography in 1890, which was long the most influential work on Tycho. According to historian of science Helge Kragh, this assessment grew out of Gassendi's opposition to Aristotelianism and Cartesianism, and fails to account for the diversity of Tycho's activities.

Tycho considered astrology to be a subject of great importance. In addition to his contributions to astronomy, he was famous in his own time also for his contributions to medicine; his herbal medicines were in use as late as the 1900s. Although the research community Tycho created in Uraniborg did not survive him, while it existed it was both a research center and an institution of education, functioning as a graduate school for Danish and foreign students in both astronomy and medicine. Tycho's success as a scientist also depended on his adroit political skills, to obtain patronage and funding for his work.

The crater Tycho on the Moon is named after him, as is the crater Tycho Brahe on Mars. The Tycho Brahe Planetarium in Copenhagen is also named after him.

HEAT1X-TYCHO BRAHE is the name of a manned private spacecraft to be launched by Copenhagen Suborbitals. Other things named after him include a bar in Zagreb and a ferry operating between Sweden and Denmark. Tycho Brahe is also the alias of one of the main characters of Penny Arcade.

See also

December 1573 lunar eclipse

History of trigonometry

Regiomontanus

Notes

References

Brahe, Tycho. ''Tychonis Brahe Dani Opera Omnia'' (in Latin). 15 vols. 1913–1929. Edited by J. L. E. Dreyer.

Brahe, Tycho. 'Astronomiæ instauratæ mechanica', 1598 European Digital Library Treasure

Bricka, Carl Frederik, ''Dansk Biografisk Lexikon'', vol. II [Beccau - Brandis], 1888. Online edition

Hoskin, M. (ed.) ''The Cambridge Concise History of Astronomy'' CUP 1999

Olson, Donald W.; Olson, Marilynn S.; Doescher, Russell L., "The Stars of ''Hamlet''," ''Sky & Telescope'' (November 1998)

Pannekoek, A. ''A History of Astronomy'' Allen & Unwin 1961

Pledge, H. ''Science since 1500'' 1939

Rybka, P. ''Katalog Gwiazdowy Heweliusza'', Warsaw 1984.

Skautrup, Peter, 1941 Den jyske lov: Text med oversattelse og ordbog. Aarhus: Universitets-forlag.

Swerdlow, N. M. ''Astronomy in the Renaissance'' in Walker 1996

Thoren, V. ''Tycho Brahe'' in Taton & Wilson CUP 1989

Walker, C. (ed.) ''Astronomy before the telescope'' British Museum Press 1996

Wesley, W. G. "The Accuracy of Tycho Brahe's Instruments," ''Journal for the History of Astronomy'', 9 (1978)

Wittendorff, Alex. 1994. ''Tyge Brahe''. Copenhagen: G. E. C. Gad.

Further reading

Kitty Ferguson: ''The nobleman and his housedog: Tycho Brahe and Johannes Kepler: the strange partnership that revolutionised science.'' London: Review, 2002 ISBN 0-7472-7022-8 (published in the US as: ''Tycho & Kepler: the unlikely partnership that forever changed our understanding of the heavens.'' New York: Walker, 2002 ISBN 0-8027-1390-4)

Joshua Gilder and Anne-Lee Gilder ''Heavenly intrigue''. New York: Doubleday, 2004 ISBN 0-385-50844-1

Arthur Koestler: ''The Sleepwalkers: A History of Man's Changing Vision of the Universe''. Hutchinson, 1959; reprinted in Arkana, 1989

Godfred Hartmann. ''Urania. Om mennesket Tyge Brahe''. Copenhagen: Gyldendal, 1989 ISBN 87-00-62763-1

Wilson & Taton. ''Planetary astronomy from the Renaissance to the rise of astrophysics'' 1989 CUP (articles by Thoren, Jarell and Schofield on the nature and history of the Tychonic astronomical model)

(analysis of individual instrument accuracies) (critical analysis of Tycho's 1004 star catalogue D. Printing date: 2009\1\12)

External links

The opening of Tycho Brahe's tomb Aarhus University.

Tycho Brahe Homepage

Brahe, Tycho MacTutor History of Mathematics

Tycho Brahe pages by Adam Mosley at Starry Messenger: An Electronic History of Astronomy, University of Cambridge

The Noble Dane: Images of Tycho Brahe. The Museum of the History of Science, Oxford, exhibits Eduard Ender's painting and other Tycho material.

Astronomiae instauratae mechanica, 1602 edition - Full digital facsimile, Lehigh University.

Astronomiae instauratae mechanica, 1602 edition - Full digital facsimile, Smithsonian Institution.

Astronomiae instauratae mechanica, 1598 edition - Full digital facsimile, the Danish Royal Library. Includes Danish and English translations.

Electronic facsimile editions of the rare book collection at the Vienna Institute of Astronomy

Brahe Bio at Skyscript

The Galileo Project article on Tycho Brahe

The Observations of Tycho Brahe

''Learned Tico Brahae, His Astronomicall Coniectur'', 1632 - Full digital facsimile, Linda Hall Library.

The play Rudolf II, by Edward Einhorn, features Tycho Brahe as a character

Tycho Brahe: the master of naked eye astronomy - background and hands on activities

Coat-of-arms of Tycho Brahe

Tycho Brahe museum, Ven, Sweden

* Category:1546 births Category:1601 deaths Category:16th-century astronomers Category:16th-century Latin-language writers Category:16th-century Danish people Category:16th-century German people Category:16th-century Czech people Category:16th-century Austrian people Category:Danish alchemists Category:Danish astrologers Category:Danish astronomers Category:Scientific instrument makers Category:Supernova discoverers Category:Danish Lutherans Category:Christian astrologers Category:Knights of the Elephant Category:University of Copenhagen alumni Category:University of Rostock alumni Category:University of Leipzig alumni Category:Danish expatriates in Germany Category:Danish expatriates in Austria Category:Danish expatriates in the Czech lands Category:People from Copenhagen

ar:تيخو براهي an:Tycho Brahe bn:টাইকো ব্রাহে zh-min-nan:Tycho Brahe be:Ціха Браге be-x-old:Тыха Брагэ bs:Tycho Brahe br:Tycho Brahe bg:Тихо Брахе ca:Tycho Brahe cs:Tycho Brahe cy:Tycho Brahe da:Tycho Brahe de:Tycho Brahe et:Tycho Brahe el:Τυχό Μπραχέ es:Tycho Brahe eo:Tycho Brahe eu:Tycho Brahe fa:تیکو براهه fr:Tycho Brahe ga:Tycho Brahe gl:Tycho Brahe ko:튀코 브라헤 hi:टैको ब्राहे hr:Tycho Brahe io:Tycho Brahe id:Tycho Brahe ia:Tycho Brahe is:Tycho Brahe it:Tycho Brahe he:טיכו ברהה jv:Tycho Brahe sw:Tycho Brahe la:Tycho Brahe lv:Tiho Brahe lb:Tycho Brahe lt:Tychas Brahė hu:Tycho Brahe mk:Тихо Брахе ml:ടൈക്കോ ബ്രാഹെ mr:टायको ब्राहे arz:تايخو برايى nl:Tycho Brahe ja:ティコ・ブラーエ no:Tycho Brahe nn:Tycho Brahe pms:Tycho Brahe nds:Tycho Brahe pl:Tycho Brahe pt:Tycho Brahe ro:Tycho Brahe ru:Браге, Тихо sah:Тихо Браге sco:Tycho Brahe scn:Tycho Brahe simple:Tycho Brahe sk:Tycho Brahe sl:Tycho Brahe sr:Тихо Брахе sh:Tycho Brahe fi:Tyko Brahe sv:Tycho Brahe tl:Tycho Brahe ta:டைக்கோ பிரா tt:Тихо Браге th:ไทโค บราเฮ tr:Tycho Brahe uk:Тихо Браге vi:Tycho Brahe vo:Tycho Brahe war:Tycho Brahe wuu:Tycho Brahe yi:טיכא בראהע zh-yue:第谷 bat-smg:Tycho Brahe zh:第谷·布拉赫

Brahe (originally ''Bragde'') is the name of a Scanian noble family that was influential in both Danish and Swedish history but has its family roots in Swedish origin. The first member of the family is speculated to have been Verner Braghde from Halland. Better documented is Peder Axelsen Brahe who appears in late 14th century records. He fathered two sons, Thorkild and Axel Axel Pedersen Brahe. What later became the Danish branch descended from Axel and what later became the Swedish, descended from Thorkild's daughter, Johanna Torkildsdotter Brahe.

Per Brahe was in 1561 granted dignity as a count by Eric XIV of Sweden and in 1620 was the family introduced on the Swedish House of Knights (''Riddarhuset'') as the first counts. The family died out in 1930, after which the foremost comital family became Lewenhaupt.

Danish family

Jørgen Thygesen Brahe (1515–1565): holder of a Seignory

Otte Brahe (1517–1571): nobleman, governor and member of the Rigsraad

Tycho Brahe (1546–1601): nobleman, astronomer, astrologer and alchemist

Jørgen Ottesen Brahe (1553–1601): holder of a Seignory

Sophia Brahe (1556–1643): horticulturalist, healer, historian and astronomer

Swedish family

Per Brahe the Elder (1520–1590): statesman

* Erik Brahe (1552–1614): Count of Visingsborg

* Gustaf Brahe (1558–1615), ''riksråd'' of Sweden – loyal to king Sigismund – and later, Polish general

* Magnus Brahe (1564–1633): Lord High Steward of Sweden

**Ebba Brahe (1596–1674): lady-in-waiting and mistress of future King Gustavus Adolphus, wife of Jakob De la Gardie

*Abraham Brahe (1569–1630): Swedish Count

**Per Brahe the Younger (1602–1680): soldier and statesman

**Nils Brahe (1604–1632): general in the Swedish army

***Nils Brahe (1633–1699): Swedish Count

Erik Brahe (1722–1756): Marshal and Colonel

Magnus Fredrik Brahe (1756–1826):Swedish Count,

* Magnus Brahe (1790–1844): statesman and soldier

References

Other sources

Carlsson, Gottfrid ''Brahe (släkt)'' ''Svenskt biografiskt lexikon'', bd 5, s. 637-641.

Weibull, Lauritz (1904) ''Sophia Brahe. Bidrag till den genealogiska forskningen i Danmark'' (Historical Journal för Skåne Country, s. 38-71)

External links

Danmarks Adels Aarbog - Register 1884-2002

Category:Swedish-language surnames Category:Swedish nobility Category:Danish nobility Category:Danish people of Swedish descent

da:Brahe fr:Brahe nl:Brahe ru:Браге sl:Brahe sv:Brahe

Coordinates	12°2′36″N77°1′42″N
Name	Johannes Kepler
Birth date	December 27, 1571
Birth place	Free Imperial City of Weil der Stadt near Stuttgart, HRE (now part of the Stuttgart Region of Baden-Württemberg, Germany)
Residence	Württemberg; Styria; Bohemia; Upper Austria
Death date	November 15, 1630
Death place	Regensburg, Electorate of Bavaria, HRE (now Germany)
Field	Astronomy, astrology, mathematics and natural philosophy
Work institutions	University of Linz
Alma mater	University of Tübingen
Advisor	Michael Maestlin
Known for	Kepler's laws of planetary motionKepler conjecture
Religion	Lutheran
Signature	Unterschrift Kepler.svg
Footnotes	}}

Johannes Kepler (; December 27, 1571 – November 15, 1630) was a German mathematician, astronomer and astrologer. A key figure in the 17th century scientific revolution, he is best known for his eponymous laws of planetary motion, codified by later astronomers, based on his works ''Astronomia nova'', ''Harmonices Mundi'', and ''Epitome of Copernican Astronomy''. These works also provided one of the foundations for Isaac Newton's theory of universal gravitation.

During his career, Kepler was a mathematics teacher at a seminary school in Graz, Austria, where he became an associate of Prince Hans Ulrich von Eggenberg. Later he became an assistant to astronomer Tycho Brahe, and eventually the imperial mathematician to Emperor Rudolf II and his two successors Matthias and Ferdinand II. He was also a mathematics teacher in Linz, Austria, and an adviser to General Wallenstein. Additionally, he did fundamental work in the field of optics, invented an improved version of the refracting telescope (the Keplerian Telescope), and mentioned the telescopic discoveries of his contemporary Galileo Galilei.

Kepler lived in an era when there was no clear distinction between astronomy and astrology, but there was a strong division between astronomy (a branch of mathematics within the liberal arts) and physics (a branch of natural philosophy). Kepler also incorporated religious arguments and reasoning into his work, motivated by the religious conviction and belief that God had created the world according to an intelligible plan that is accessible through the natural light of reason. Kepler described his new astronomy as "celestial physics", as "an excursion into Aristotle's ''Metaphysics''", and as "a supplement to Aristotle's ''On the Heavens''", transforming the ancient tradition of physical cosmology by treating astronomy as part of a universal mathematical physics.

Early years

Johannes Kepler was born on December 27, 1571, at the Free Imperial City of Weil der Stadt (now part of the Stuttgart Region in the German state of Baden-Württemberg, 30 km west of Stuttgart's center). His grandfather, Sebald Kepler, had been Lord Mayor of that town but, by the time Johannes was born, he had two brothers and one sister and the Kepler family fortune was in decline. His father, Heinrich Kepler, earned a precarious living as a mercenary, and he left the family when Johannes was five years old. He was believed to have died in the Eighty Years' War in the Netherlands. His mother Katharina Guldenmann, an inn-keeper's daughter, was a healer and herbalist who was later tried for witchcraft. Born prematurely, Johannes claimed to have been a weak and sickly child. He was, however, a brilliant child; he often impressed travelers at his grandfather's inn with his phenomenal mathematical faculty.

He was introduced to astronomy at an early age, and developed a love for it that would span his entire life. At age six, he observed the Great Comet of 1577, writing that he "was taken by [his] mother to a high place to look at it." At age nine, he observed another astronomical event, a lunar eclipse in 1580, recording that he remembered being "called outdoors" to see it and that the moon "appeared quite red". However, childhood smallpox left him with weak vision and crippled hands, limiting his ability in the observational aspects of astronomy.

In 1589, after moving through grammar school, Latin school, and seminary at Maulbronn, Kepler attended Tübinger Stift at the University of Tübingen. There, he studied philosophy under Vitus Müller and theology under Jacob Heerbrand (a student of Philipp Melanchthon at Wittenberg), who also taught Michael Maestlin while he was a student, until he became Chancellor at Tübingen in 1590. He proved himself to be a superb mathematician and earned a reputation as a skillful astrologer, casting horoscopes for fellow students. Under the instruction of Michael Maestlin, Tübingen's professor of mathematics from 1583 to 1631, Despite his desire to become a minister, near the end of his studies Kepler was recommended for a position as teacher of mathematics and astronomy at the Protestant school in Graz (later the University of Graz). He accepted the position in April 1594, at the age of 23.

Graz (1594–1600)

''Mysterium Cosmographicum''

Johannes Kepler's first major astronomical work, ''Mysterium Cosmographicum'' (''The Cosmographic Mystery''), was the first published defense of the Copernican system. Kepler claimed to have had an epiphany on July 19, 1595, while teaching in Graz, demonstrating the periodic conjunction of Saturn and Jupiter in the zodiac; he realized that regular polygons bound one inscribed and one circumscribed circle at definite ratios, which, he reasoned, might be the geometrical basis of the universe. After failing to find a unique arrangement of polygons that fit known astronomical observations (even with extra planets added to the system), Kepler began experimenting with 3-dimensional polyhedra. He found that each of the five Platonic solids could be uniquely inscribed and circumscribed by spherical orbs; nesting these solids, each encased in a sphere, within one another would produce six layers, corresponding to the six known planets—Mercury, Venus, Earth, Mars, Jupiter, and Saturn. By ordering the solids correctly—octahedron, icosahedron, dodecahedron, tetrahedron, cube—Kepler found that the spheres could be placed at intervals corresponding (within the accuracy limits of available astronomical observations) to the relative sizes of each planet’s path, assuming the planets circle the Sun. Kepler also found a formula relating the size of each planet’s orb to the length of its orbital period: from inner to outer planets, the ratio of increase in orbital period is twice the difference in orb radius. However, Kepler later rejected this formula, because it was not precise enough.

As he indicated in the title, Kepler thought he had revealed God’s geometrical plan for the universe. Much of Kepler’s enthusiasm for the Copernican system stemmed from his theological convictions about the connection between the physical and the spiritual; the universe itself was an image of God, with the Sun corresponding to the Father, the stellar sphere to the Son, and the intervening space between to the Holy Spirit. His first manuscript of ''Mysterium'' contained an extensive chapter reconciling heliocentrism with biblical passages that seemed to support geocentrism.

With the support of his mentor Michael Maestlin, Kepler received permission from the Tübingen university senate to publish his manuscript, pending removal of the Bible exegesis and the addition of a simpler, more understandable description of the Copernican system as well as Kepler’s new ideas. ''Mysterium'' was published late in 1596, and Kepler received his copies and began sending them to prominent astronomers and patrons early in 1597; it was not widely read, but it established Kepler’s reputation as a highly skilled astronomer. The effusive dedication, to powerful patrons as well as to the men who controlled his position in Graz, also provided a crucial doorway into the patronage system.

Though the details would be modified in light of his later work, Kepler never relinquished the Platonist polyhedral-spherist cosmology of ''Mysterium Cosmographicum''. His subsequent main astronomical works were in some sense only further developments of it, concerned with finding more precise inner and outer dimensions for the spheres by calculating the eccentricities of the planetary orbits within it. In 1621 Kepler published an expanded second edition of ''Mysterium'', half as long again as the first, detailing in footnotes the corrections and improvements he had achieved in the 25 years since its first publication.

In terms of the impact of ''Mysterium'', it can be seen as an important first step in modernizing Copernicus' theory. There is no doubt that Copernicus' "De Revolutionibus" seeks to advance a sun-centered system, but in this book he had to resort to Ptolemaic devices (viz., epicycles and eccentric circles) in order to explain the change in planets' orbital speed. Furthermore, Copernicus continued to use as a point of reference the center of the earth's orbit rather than that of the sun, as he says, "as an aid to calculation and in order not to confuse the reader by diverging too much from Ptolemy." Therefore, although the thesis of the "Mysterium Cosmographicum" was in error, modern astronomy owes much to this work "since it represents the first step in cleansing the Copernican system of the remnants of the Ptolemaic theory still clinging to it."

Marriage to Barbara Müller

In December 1595, Kepler was introduced to Barbara Müller, a 23-year-old widow (twice over) with a young daughter, Gemma van Dvijneveldt, and he began courting her. Müller, heir to the estates of her late husbands, was also the daughter of a successful mill owner. Her father Jobst initially opposed a marriage despite Kepler's nobility; though he had inherited his grandfather's nobility, Kepler's poverty made him an unacceptable match. Jobst relented after Kepler completed work on ''Mysterium'', but the engagement nearly fell apart while Kepler was away tending to the details of publication. However, church officials—who had helped set up the match—pressured the Müllers to honor their agreement. Barbara and Johannes were married on April 27, 1597.

In the first years of their marriage, the Keplers had two children (Heinrich and Susanna), both of whom died in infancy. In 1602, they had a daughter (Susanna); in 1604, a son (Friedrich); and in 1607, another son (Ludwig).

Other research

Following the publication of ''Mysterium'' and with the blessing of the Graz school inspectors, Kepler began an ambitious program to extend and elaborate his work. He planned four additional books: one on the stationary aspects of the universe (the Sun and the fixed stars); one on the planets and their motions; one on the physical nature of planets and the formation of geographical features (focused especially on Earth); and one on the effects of the heavens on the Earth, to include atmospheric optics, meteorology and astrology.

He also sought the opinions of many of the astronomers to whom he had sent ''Mysterium'', among them Reimarus Ursus (Nicolaus Reimers Bär)—the imperial mathematician to Rudolph II and a bitter rival of Tycho Brahe. Ursus did not reply directly, but republished Kepler's flattering letter to pursue his priority dispute over (what is now called) the Tychonic system with Tycho. Despite this black mark, Tycho also began corresponding with Kepler, starting with a harsh but legitimate critique of Kepler's system; among a host of objections, Tycho took issue with the use of inaccurate numerical data taken from Copernicus. Through their letters, Tycho and Kepler discussed a broad range of astronomical problems, dwelling on lunar phenomena and Copernican theory (particularly its theological viability). But without the significantly more accurate data of Tycho's observatory, Kepler had no way to address many of these issues.

Instead, he turned his attention to chronology and "harmony," the numerological relationships among music, mathematics and the physical world, and their astrological consequences. By assuming the Earth to possess a soul (a property he would later invoke to explain how the sun causes the motion of planets), he established a speculative system connecting astrological aspects and astronomical distances to weather and other earthly phenomena. By 1599, however, he again felt his work limited by the inaccuracy of available data—just as growing religious tension was also threatening his continued employment in Graz. In December of that year, Tycho invited Kepler to visit him in Prague; on January 1, 1600 (before he even received the invitation), Kepler set off in the hopes that Tycho's patronage could solve his philosophical problems as well as his social and financial ones.

Prague (1600–1612)

Work for Tycho Brahe

On February 4, 1600, Kepler met Tycho Brahe and his assistants Franz Tengnagel and Longomontanus at Benátky nad Jizerou (35 km from Prague), the site where Tycho's new observatory was being constructed. Over the next two months he stayed as a guest, analyzing some of Tycho's observations of Mars; Tycho guarded his data closely, but was impressed by Kepler's theoretical ideas and soon allowed him more access. Kepler planned to test his theory from ''Mysterium Cosmographicum'' based on the Mars data, but he estimated that the work would take up to two years (since he was not allowed to simply copy the data for his own use). With the help of Johannes Jessenius, Kepler attempted to negotiate a more formal employment arrangement with Tycho, but negotiations broke down in an angry argument and Kepler left for Prague on April 6. Kepler and Tycho soon reconciled and eventually reached an agreement on salary and living arrangements, and in June, Kepler returned home to Graz to collect his family.

Political and religious difficulties in Graz dashed his hopes of returning immediately to Tycho; in hopes of continuing his astronomical studies, Kepler sought an appointment as mathematician to Archduke Ferdinand. To that end, Kepler composed an essay—dedicated to Ferdinand—in which he proposed a force-based theory of lunar motion: "In Terra inest virtus, quae Lunam ciet" ("There is a force in the earth which causes the moon to move"). Though the essay did not earn him a place in Ferdinand's court, it did detail a new method for measuring lunar eclipses, which he applied during the July 10 eclipse in Graz. These observations formed the basis of his explorations of the laws of optics that would culminate in ''Astronomiae Pars Optica''.

On August 2, 1600, after refusing to convert to Catholicism, Kepler and his family were banished from Graz. Several months later, Kepler returned, now with the rest of his household, to Prague. Through most of 1601, he was supported directly by Tycho, who assigned him to analyzing planetary observations and writing a tract against Tycho's (by then deceased) rival, Ursus. In September, Tycho secured him a commission as a collaborator on the new project he had proposed to the emperor: the ''Rudolphine Tables'' that should replace the ''Prutenic Tables'' of Erasmus Reinhold. Two days after Tycho's unexpected death on October 24, 1601, Kepler was appointed his successor as imperial mathematician with the responsibility to complete his unfinished work. The next 11 years as imperial mathematician would be the most productive of his life.

Advisor to Emperor Rudolph II

Kepler's primary obligation as imperial mathematician was to provide astrological advice to the emperor. Though Kepler took a dim view of the attempts of contemporary astrologers to precisely predict the future or divine specific events, he had been casting detailed horoscopes for friends, family and patrons since his time as a student in Tübingen. In addition to horoscopes for allies and foreign leaders, the emperor sought Kepler's advice in times of political trouble (though Kepler's recommendations were based more on common sense than the stars). Rudolph was actively interested in the work of many of his court scholars (including numerous alchemists) and kept up with Kepler's work in physical astronomy as well.

Officially, the only acceptable religious doctrines in Prague were Catholic and Utraquist, but Kepler's position in the imperial court allowed him to practice his Lutheran faith unhindered. The emperor nominally provided an ample income for his family, but the difficulties of the over-extended imperial treasury meant that actually getting hold of enough money to meet financial obligations was a continual struggle. Partly because of financial troubles, his life at home with Barbara was unpleasant, marred with bickering and bouts of sickness. Court life, however, brought Kepler into contact with other prominent scholars (Johannes Matthäus Wackher von Wackhenfels, Jost Bürgi, David Fabricius, Martin Bachazek, and Johannes Brengger, among others) and astronomical work proceeded rapidly.

''Astronomiae Pars Optica''

As he slowly continued analyzing Tycho's Mars observations—now available to him in their entirety—and began the slow process of tabulating the ''Rudolphine Tables'', Kepler also picked up the investigation of the laws of optics from his lunar essay of 1600. Both lunar and solar eclipses presented unexplained phenomena, such as unexpected shadow sizes, the red color of a total lunar eclipse, and the reportedly unusual light surrounding a total solar eclipse. Related issues of atmospheric refraction applied to ''all'' astronomical observations. Through most of 1603, Kepler paused his other work to focus on optical theory; the resulting manuscript, presented to the emperor on January 1, 1604, was published as ''Astronomiae Pars Optica'' (''The Optical Part of Astronomy''). In it, Kepler described the inverse-square law governing the intensity of light, reflection by flat and curved mirrors, and principles of pinhole cameras, as well as the astronomical implications of optics such as parallax and the apparent sizes of heavenly bodies. He also extended his study of optics to the human eye, and is generally considered by neuroscientists to be the first to recognize that images are projected inverted and reversed by the eye's lens onto the retina. The solution to this dilemma was not of particular importance to Kepler as he did not see it as pertaining to optics, although he did suggest that the image was later corrected "in the hollows of the brain" due to the "activity of the Soul." Today, ''Astronomiae Pars Optica'' is generally recognized as the foundation of modern optics (though the law of refraction is conspicuously absent).

The Supernova of 1604

In October 1604, a bright new evening star (SN 1604) appeared, but Kepler did not believe the rumors until he saw it himself. Kepler began systematically observing the star. Astrologically, the end of 1603 marked the beginning of a fiery trigon, the start of the ca. 800-year cycle of great conjunctions; astrologers associated the two previous such periods with the rise of Charlemagne (ca. 800 years earlier) and the birth of Christ (ca. 1600 years earlier), and thus expected events of great portent, especially regarding the emperor. It was in this context, as the imperial mathematician and astrologer to the emperor, that Kepler described the new star two years later in his ''De Stella Nova''. In it, Kepler addressed the star's astronomical properties while taking a skeptical approach to the many astrological interpretations then circulating. He noted its fading luminosity, speculated about its origin, and used the lack of observed parallax to argue that it was in the sphere of fixed stars, further undermining the doctrine of the immutability of the heavens (the idea accepted since Aristotle that the celestial spheres were perfect and unchanging). The birth of a new star implied the variability of the heavens. In an appendix, Kepler also discussed the recent chronology work of the Polish historian Laurentius Suslyga; he calculated that, if Suslyga was correct that accepted timelines were four years behind, then the Star of Bethlehem—analogous to the present new star—would have coincided with the first great conjunction of the earlier 800-year cycle.

''Astronomia nova''

The extended line of research that culminated in ''Astronomia nova'' (''A New Astronomy'')—including the first two laws of planetary motion—began with the analysis, under Tycho's direction, of Mars' orbit. Kepler calculated and recalculated various approximations of Mars' orbit using an equant (the mathematical tool that Copernicus had eliminated with his system), eventually creating a model that generally agreed with Tycho's observations to within two arcminutes (the average measurement error). But he was not satisfied with the complex and still slightly inaccurate result; at certain points the model differed from the data by up to eight arcminutes. The wide array of traditional mathematical astronomy methods having failed him, Kepler set about trying to fit an ovoid orbit to the data.

Within Kepler's religious view of the cosmos, the Sun (a symbol of God the Father) was the source of motive force in the solar system. As a physical basis, Kepler drew by analogy on William Gilbert's theory of the magnetic soul of the Earth from ''De Magnete'' (1600) and on his own work on optics. Kepler supposed that the motive power (or motive ''species'') radiated by the Sun weakens with distance, causing faster or slower motion as planets move closer or farther from it. Perhaps this assumption entailed a mathematical relationship that would restore astronomical order. Based on measurements of the aphelion and perihelion of the Earth and Mars, he created a formula in which a planet's rate of motion is inversely proportional to its distance from the Sun. Verifying this relationship throughout the orbital cycle, however, required very extensive calculation; to simplify this task, by late 1602 Kepler reformulated the proportion in terms of geometry: ''planets sweep out equal areas in equal times''—Kepler's second law of planetary motion.

He then set about calculating the entire orbit of Mars, using the geometrical rate law and assuming an egg-shaped ovoid orbit. After approximately 40 failed attempts, in early 1605 he at last hit upon the idea of an ellipse, which he had previously assumed to be too simple a solution for earlier astronomers to have overlooked. Finding that an elliptical orbit fit the Mars data, he immediately concluded that ''all planets move in ellipses, with the sun at one focus''—Kepler's first law of planetary motion. Because he employed no calculating assistants, however, he did not extend the mathematical analysis beyond Mars. By the end of the year, he completed the manuscript for ''Astronomia nova'', though it would not be published until 1609 due to legal disputes over the use of Tycho's observations, the property of his heirs.

''Dioptrice'', ''Somnium'' manuscript and other work

In the years following the completion of ''Astronomia Nova'', most of Kepler's research was focused on preparations for the ''Rudolphine Tables'' and a comprehensive set of ephemerides (specific predictions of planet and star positions) based on the table (though neither would be completed for many years). He also attempted (unsuccessfully) to begin a collaboration with Italian astronomer Giovanni Antonio Magini. Some of his other work dealt with chronology, especially the dating of events in the life of Jesus, and with astrology, especially criticism of dramatic predictions of catastrophe such as those of Helisaeus Roeslin.

Kepler and Roeslin engaged in series of published attacks and counter-attacks, while physician Philip Feselius published a work dismissing astrology altogether (and Roeslin's work in particular). In response to what Kepler saw as the excesses of astrology on the one hand and overzealous rejection of it on the other, Kepler prepared ''Tertius Interveniens'' (''Third-party Interventions''). Nominally this work—presented to the common patron of Roeslin and Feselius—was a neutral mediation between the feuding scholars, but it also set out Kepler's general views on the value of astrology, including some hypothesized mechanisms of interaction between planets and individual souls. While Kepler considered most traditional rules and methods of astrology to be the "evil-smelling dung" in which "an industrious hen" scrapes, there was "also perhaps a good little grain" to be found by the conscientious scientific astrologer.

In the first months of 1610, Galileo Galilei—using his powerful new telescope—discovered four satellites orbiting Jupiter. Upon publishing his account as ''Sidereus Nuncius'' (''Starry Messenger''), Galileo sought the opinion of Kepler, in part to bolster the credibility of his observations. Kepler responded enthusiastically with a short published reply, ''Dissertatio cum Nuncio Sidereo'' (''Conversation with the Starry Messenger''). He endorsed Galileo's observations and offered a range of speculations about the meaning and implications of Galileo's discoveries and telescopic methods, for astronomy and optics as well as cosmology and astrology. Later that year, Kepler published his own telescopic observations of the moons in ''Narratio de Jovis Satellitibus'', providing further support of Galileo. To Kepler's disappointment, however, Galileo never published his reactions (if any) to ''Astronomia Nova''.

After hearing of Galileo's telescopic discoveries, Kepler also started a theoretical and experimental investigation of telescopic optics using a telescope borrowed from Duke Ernest of Cologne. The resulting manuscript was completed in September 1610 and published as ''Dioptrice'' in 1611. In it, Kepler set out the theoretical basis of double-convex converging lenses and double-concave diverging lenses—and how they are combined to produce a Galilean telescope—as well as the concepts of real vs. virtual images, upright vs. inverted images, and the effects of focal length on magnification and reduction. He also described an improved telescope—now known as the ''astronomical'' or ''Keplerian telescope''—in which two convex lenses can produce higher magnification than Galileo's combination of convex and concave lenses.

Around 1611, Kepler circulated a manuscript of what would eventually be published (posthumously) as ''Somnium'' (''The Dream''). Part of the purpose of ''Somnium'' was to describe what practicing astronomy would be like from the perspective of another planet, to show the feasibility of a non-geocentric system. The manuscript, which disappeared after changing hands several times, described a fantastic trip to the moon; it was part allegory, part autobiography, and part treatise on interplanetary travel (and is sometimes described as the first work of science fiction). Years later, a distorted version of the story may have instigated the witchcraft trial against his mother, as the mother of the narrator consults a demon to learn the means of space travel. Following her eventual acquittal, Kepler composed 223 footnotes to the story—several times longer than the actual text—which explained the allegorical aspects as well as the considerable scientific content (particularly regarding lunar geography) hidden within the text.

Work in mathematics and physics

As a New Year's gift that year, he also composed for his friend and some-time patron Baron Wackher von Wackhenfels a short pamphlet entitled ''Strena Seu de Nive Sexangula'' (''A New Year's Gift of Hexagonal Snow''). In this treatise, he published the first description of the hexagonal symmetry of snowflakes and, extending the discussion into a hypothetical atomistic physical basis for the symmetry and posed what later became known as the Kepler conjecture, a statement about the most efficient arrangement for packing spheres. Kepler was one of the pioneers of the mathematical applications of infinitesimals, see Law of Continuity.

Personal and political troubles

In 1611, the growing political-religious tension in Prague came to a head. Emperor Rudolph—whose health was failing—was forced to abdicate as King of Bohemia by his brother Matthias. Both sides sought Kepler's astrological advice, an opportunity he used to deliver conciliatory political advice (with little reference to the stars, except in general statements to discourage drastic action). However, it was clear that Kepler's future prospects in the court of Matthias were dim.

Also in that year, Barbara Kepler contracted Hungarian spotted fever, then began having seizures. As Barbara was recovering, Kepler's three children all fell sick with smallpox; Friedrich, 6, died. Following his son's death, Kepler sent letters to potential patrons in Württemberg and Padua. At the University of Tübingen in Württemberg, concerns over Kepler's perceived Calvinist heresies in violation of the Augsburg Confession and the Formula of Concord prevented his return. The University of Padua—on the recommendation of the departing Galileo—sought Kepler to fill the mathematics professorship, but Kepler, preferring to keep his family in German territory, instead travelled to Austria to arrange a position as teacher and district mathematician in Linz. However, Barbara relapsed into illness and died shortly after Kepler's return.

Kepler postponed the move to Linz and remained in Prague until Rudolph's death in early 1612, though between political upheaval, religious tension, and family tragedy (along with the legal dispute over his wife's estate), Kepler could do no research. Instead, he pieced together a chronology manuscript, ''Eclogae Chronicae'', from correspondence and earlier work. Upon succession as Holy Roman Emperor, Matthias re-affirmed Kepler's position (and salary) as imperial mathematician but allowed him to move to Linz.

Linz and elsewhere (1612–1630)

In Linz, Kepler's primary responsibilities (beyond completing the ''Rudolphine Tables'') were teaching at the district school and providing astrological and astronomical services. In his first years there, he enjoyed financial security and religious freedom relative to his life in Prague—though he was excluded from Eucharist by his Lutheran church over his theological scruples. His first publication in Linz was ''De vero Anno'' (1613), an expanded treatise on the year of Christ's birth; he also participated in deliberations on whether to introduce Pope Gregory's reformed calendar to Protestant German lands; that year he also wrote the influential mathematical treatise ''Nova stereometria doliorum vinariorum'', on measuring the volume of containers such as wine barrels (though it would not be published until 1615).

Second marriage

On October 30, 1613, Kepler married the 24-year-old Susanna Reuttinger. Following the death of his first wife Barbara, Kepler had considered 11 different matches. He eventually returned to Reuttinger (the fifth match) who, he wrote, "won me over with love, humble loyalty, economy of household, diligence, and the love she gave the stepchildren." The first three children of this marriage (Margareta Regina, Katharina, and Sebald) died in childhood. Three more survived into adulthood: Cordula (b. 1621); Fridmar (b. 1623); and Hildebert (b. 1625). According to Kepler's biographers, this was a much happier marriage than his first.

''Epitome of Copernican Astronomy'', calendars and the witch trial of his mother

Since completing the ''Astronomia nova'', Kepler had intended to compose an astronomy textbook. In 1615, he completed the first of three volumes of ''Epitome astronomia Copernicanae'' (''Epitome of Copernican Astronomy''); the first volume (books I-III) was printed in 1617, the second (book IV) in 1620, and the third (books V-VII) in 1621. Despite the title, which referred simply to heliocentrism, Kepler's textbook culminated in his own ellipse-based system. The ''Epitome'' became Kepler's most influential work. It contained all three laws of planetary motion and attempted to explain heavenly motions through physical causes. Though it explicitly extended the first two laws of planetary motion (applied to Mars in ''Astronomia nova'') to all the planets as well as the Moon and the Medicean satellites of Jupiter, it did not explain how elliptical orbits could be derived from observational data.

As a spin-off from the ''Rudolphine Tables'' and the related ''Ephemerides'', Kepler published astrological calendars, which were very popular and helped offset the costs of producing his other work—especially when support from the Imperial treasury was withheld. In his calendars—six between 1617 and 1624—Kepler forecast planetary positions and weather as well as political events; the latter were often cannily accurate, thanks to his keen grasp of contemporary political and theological tensions. By 1624, however, the escalation of those tensions and the ambiguity of the prophecies meant political trouble for Kepler himself; his final calendar was publicly burned in Graz.

In 1615, Ursula Reingold, a woman in a financial dispute with Kepler's brother Christoph, claimed Kepler's mother Katharina had made her sick with an evil brew. The dispute escalated, and in 1617, Katharina was accused of witchcraft; witchcraft trials were relatively common in central Europe at this time. Beginning in August 1620 she was imprisoned for fourteen months. She was released in October 1621, thanks in part to the extensive legal defense drawn up by Kepler. The accusers had no stronger evidence than rumors, along with a distorted, second-hand version of Kepler's ''Somnium'', in which a woman mixes potions and enlists the aid of a demon. Katharina was subjected to ''territio verbalis'', a graphic description of the torture awaiting her as a witch, in a final attempt to make her confess. Throughout the trial, Kepler postponed his other work to focus on his "harmonic theory". The result, published in 1619, was ''Harmonices Mundi'' ("Harmony of the Worlds").

''Harmonices Mundi''

Kepler was convinced "that the geometrical things have provided the Creator with the model for decorating the whole world." In ''Harmony'', he attempted to explain the proportions of the natural world—particularly the astronomical and astrological aspects—in terms of music. The central set of "harmonies" was the ''musica universalis'' or "music of the spheres," which had been studied by Pythagoras, Ptolemy and many others before Kepler; in fact, soon after publishing ''Harmonices Mundi'', Kepler was embroiled in a priority dispute with Robert Fludd, who had recently published his own harmonic theory.

Kepler began by exploring regular polygons and regular solids, including the figures that would come to be known as Kepler's solids. From there, he extended his harmonic analysis to music, meteorology and astrology; harmony resulted from the tones made by the souls of heavenly bodies—and in the case of astrology, the interaction between those tones and human souls. In the final portion of the work (Book V), Kepler dealt with planetary motions, especially relationships between orbital velocity and orbital distance from the Sun. Similar relationships had been used by other astronomers, but Kepler—with Tycho's data and his own astronomical theories—treated them much more precisely and attached new physical significance to them.

Among many other harmonies, Kepler articulated what came to be known as the third law of planetary motion. He then tried many combinations until he discovered that (approximately) "''The square of the periodic times are to each other as the cubes of the mean distances''." Although he gives the date of this epiphany (March 8, 1618), he does not give any details about how he arrived at this conclusion. However, the wider significance for planetary dynamics of this purely kinematical law was not realized until the 1660s. For when conjoined with Christian Huygens' newly discovered law of centrifugal force it enabled Isaac Newton, Edmund Halley and perhaps Christopher Wren and Robert Hooke to demonstrate independently that the presumed gravitational attraction between the Sun and its planets decreased with the square of the distance between them. This refuted the traditional assumption of scholastic physics that the power of gravitational attraction remained constant with distance whenever it applied between two bodies, such as was assumed by Kepler and also by Galileo in his mistaken universal law that gravitational fall is uniformly accelerated, and also by Galileo's student Borrelli in his 1666 celestial mechanics.

''Rudolphine Tables'' and his last years

In 1623, Kepler at last completed the ''Rudolphine Tables'', which at the time was considered his major work. However, due to the publishing requirements of the emperor and negotiations with Tycho Brahe's heir, it would not be printed until 1627. In the meantime religious tension—the root of the ongoing Thirty Years' War—once again put Kepler and his family in jeopardy. In 1625, agents of the Catholic Counter-Reformation placed most of Kepler's library under seal, and in 1626 the city of Linz was besieged. Kepler moved to Ulm, where he arranged for the printing of the ''Tables'' at his own expense.

In 1628, following the military successes of the Emperor Ferdinand's armies under General Wallenstein, Kepler became an official advisor to Wallenstein. Though not the general's court astrologer per se, Kepler provided astronomical calculations for Wallenstein's astrologers and occasionally wrote horoscopes himself. In his final years, Kepler spent much of his time traveling, from the imperial court in Prague to Linz and Ulm to a temporary home in Sagan, and finally to Regensburg. Soon after arriving in Regensburg, Kepler fell ill. He died on November 15, 1630, and was buried there; his burial site was lost after the Swedish army destroyed the churchyard. Only Kepler's self-authored poetic epitaph survived the times:

:''Mensus eram coelos, nunc terrae metior umbras'' :''Mens coelestis erat, corporis umbra iacet.''

:I measured the skies, now the shadows I measure :Skybound was the mind, earthbound the body rests.

Reception of his astronomy

Kepler's laws were not immediately accepted. Several major figures such as Galileo and René Descartes completely ignored Kepler's ''Astronomia nova.'' Many astronomers, including Kepler's teacher, Michael Maestlin, objected to Kepler's introduction of physics into his astronomy. Some adopted compromise positions. Ismael Boulliau accepted elliptical orbits but replaced Kepler's area law with uniform motion in respect to the empty focus of the ellipse while Seth Ward used an elliptical orbit with motions defined by an equant.

Several astronomers tested Kepler's theory, and its various modifications, against astronomical observations. Two transits of Venus and Mercury across the face of the sun provided sensitive tests of the theory, under circumstances when these planets could not normally be observed. In the case of the transit of Mercury in 1631, Kepler had been extremely uncertain of the parameters for Mercury, and advised observers to look for the transit the day before and after the predicted date. Pierre Gassendi observed the transit on the date predicted, a confirmation of Kepler's prediction. This was the first observation of a transit of Mercury. However, his attempt to observe the transit of Venus just one month later, was unsuccessful due to inaccuracies in the Rudolphine Tables. Gassendi did not realize that it was not visible from most of Europe, including Paris. Jeremiah Horrocks, who observed the 1639 Venus transit, had used his own observations to adjust the parameters of the Keplerian model, predicted the transit, and then built apparatus to observe the transit. He remained a firm advocate of the Keplerian model.

''Epitome of Copernican Astronomy'' was read by astronomers throughout Europe, and following Kepler's death it was the main vehicle for spreading Kepler's ideas. Between 1630 and 1650, it was the most widely used astronomy textbook, winning many converts to ellipse-based astronomy. However, few adopted his ideas on the physical basis for celestial motions. In the late 17th century, a number of physical astronomy theories drawing from Kepler's work—notably those of Giovanni Alfonso Borelli and Robert Hooke—began to incorporate attractive forces (though not the quasi-spiritual motive species postulated by Kepler) and the Cartesian concept of inertia. This culminated in Isaac Newton's ''Principia Mathematica'' (1687), in which Newton derived Kepler's laws of planetary motion from a force-based theory of universal gravitation.

Historical and cultural legacy

Beyond his role in the historical development of astronomy and natural philosophy, Kepler has loomed large in the philosophy and historiography of science. Kepler and his laws of motion were central to early histories of astronomy such as Jean Etienne Montucla’s 1758 ''Histoire des mathématiques'' and Jean-Baptiste Delambre's 1821 ''Histoire de l’astronomie moderne''. These and other histories written from an Enlightenment perspective treated Kepler's metaphysical and religious arguments with skepticism and disapproval, but later Romantic-era natural philosophers viewed these elements as central to his success. William Whewell, in his influential ''History of the Inductive Sciences'' of 1837, found Kepler to be the archetype of the inductive scientific genius; in his ''Philosophy of the Inductive Sciences'' of 1840, Whewell held Kepler up as the embodiment of the most advanced forms of scientific method. Similarly, Ernst Friedrich Apelt—the first to extensively study Kepler's manuscripts, after their purchase by Catherine the Great—identified Kepler as a key to the "Revolution of the sciences". Apelt, who saw Kepler's mathematics, aesthetic sensibility, physical ideas, and theology as part of a unified system of thought, produced the first extended analysis of Kepler's life and work.

Modern translations of a number of Kepler's books appeared in the late-nineteenth and early-twentieth centuries, the systematic publication of his collected works began in 1937 (and is nearing completion in the early 21st century), and Max Caspar's Kepler biography was published in 1948. However, Alexandre Koyré's work on Kepler was, after Apelt, the first major milestone in historical interpretations of Kepler's cosmology and its influence. In the 1930s and 1940s Koyré, and a number of others in the first generation of professional historians of science, described the "Scientific Revolution" as the central event in the history of science, and Kepler as a (perhaps the) central figure in the revolution. Koyré placed Kepler's theorization, rather than his empirical work, at the center of the intellectual transformation from ancient to modern world-views. Since the 1960s, the volume of historical Kepler scholarship has expanded greatly, including studies of his astrology and meteorology, his geometrical methods, the role of his religious views in his work, his literary and rhetorical methods, his interaction with the broader cultural and philosophical currents of his time, and even his role as an historian of science.

The debate over Kepler's place in the Scientific Revolution has also produced a wide variety of philosophical and popular treatments. One of the most influential is Arthur Koestler's 1959 ''The Sleepwalkers'', in which Kepler is unambiguously the hero (morally and theologically as well as intellectually) of the revolution. Influential philosophers of science—such as Charles Sanders Peirce, Norwood Russell Hanson, Stephen Toulmin, and Karl Popper—have repeatedly turned to Kepler: examples of incommensurability, analogical reasoning, falsification, and many other philosophical concepts have been found in Kepler's work. Physicist Wolfgang Pauli even used Kepler's priority dispute with Robert Fludd to explore the implications of analytical psychology on scientific investigation. A well-received, if fanciful, historical novel by John Banville, ''Kepler'' (1981), explored many of the themes developed in Koestler's non-fiction narrative and in the philosophy of science. Somewhat more fanciful is a recent work of nonfiction, ''Heavenly Intrigue'' (2004), suggesting that Kepler murdered Tycho Brahe to gain access to his data. Kepler has acquired a popular image as an icon of scientific modernity and a man before his time; science popularizer Carl Sagan described him as "the first astrophysicist and the last scientific astrologer."

In Austria, Johannes Kepler left behind such a historical legacy that he was one of the motifs of a silver collector's coin: the 10-euro Johannes Kepler silver coin, minted on September 10, 2002. The reverse side of the coin has a portrait of Kepler, who spent some time teaching in Graz and the surrounding areas. Kepler was acquainted with Prince Hans Ulrich von Eggenberg personally, and he probably influenced the construction of Eggenberg Castle (the motif of the obverse of the coin). In front of him on the coin is the model of nested spheres and polyhedra from ''Mysterium Cosmographicum''.

In 2009, NASA named the Kepler Mission for Kepler's contributions to the field of astronomy.

In New Zealand's Fiordland National Park there is also a range of Mountains Named after Kepler, called the Kepler Mountains and a Three Day Walking Trail known as the Kepler Track through the Mountains of the same name.

Veneration

Kepler is honored together with Nicolaus Copernicus with a feast day on the liturgical calendar of the Episcopal Church (USA) on May 23.

Works

''Mysterium cosmographicum'' (''The Sacred Mystery of the Cosmos'') (1596)

''De Fundamentis Astrologiae Certioribus'' (''Concerning the More Certain Fundamentals of Astrology'') (1601)

''Astronomiae Pars Optica'' (''The Optical Part of Astronomy'') (1604)

''De Stella nova in pede Serpentarii'' (''On the New Star in Ophiuchus's Foot'') (1604)

''Astronomia nova'' (''New Astronomy'') (1609)

''Tertius Interveniens'' (''Third-party Interventions'') (1610)

''Dissertatio cum Nuncio Sidereo'' (''Conversation with the Starry Messenger'') (1610)

''Dioptrice'' (1611)

''De nive sexangula'' (''On the Six-Cornered Snowflake'') (1611)

''De vero Anno, quo aeternus Dei Filius humanam naturam in Utero benedictae Virginis Mariae assumpsit'' (1613)

''Eclogae Chronicae'' (1615, published with ''Dissertatio cum Nuncio Sidereo'')

''Nova stereometria doliorum vinariorum'' (''New Stereometry of Wine Barrels'') (1615)

''Epitome astronomiae Copernicanae'' (''Epitome of Copernican Astronomy'') (published in three parts from 1618–1621)

''Harmonice Mundi'' (''Harmony of the Worlds'') (1619)

''Mysterium cosmographicum'' (''The Sacred Mystery of the Cosmos'') 2nd Edition (1621)

''Tabulae Rudolphinae'' (''Rudolphine Tables'') (1627)

''Somnium'' (''The Dream'') (1634)

See also

Named in his honor

Kepler's laws of planetary motion for astronomical calculations

The Kepler Mission, a space photometer designed to search for Earth-like planets launched by NASA on March 6, 2009

The Johannes Kepler ATV, the second Automatic Transfer Vehicle (ATV) launched by ESA to resupply the ISS. The ATV launched in February 2011 and deorbited in June 2011.

The Kepler Solids, a set of geometrical constructions, two of which were described by him

The Kepler Mountains and the Kepler Track on the South Island of New Zealand

Kepler's Star, Supernova 1604, which he observed and described

Kepler, a crater on the moon

Kepler, a crater on Mars

1134 Kepler, an asteroid

Kepler, an opera by Philip Glass

Die Harmonie der Welt, an opera by Paul Hindemith

Johannes Kepler University Linz: In 1975, nine years after its founding, the College for Social and Economic Sciences Linz (Austria) was renamed Johannes Kepler University Linz in honor of Johannes Kepler, since he wrote his magnum opus ''Harmonice Mundi'' in Linz.

Kepler College, Seattle, Washington

Numerous schools, streets, observatories and others named after him, e.g.:

* Kepler Gymnasium (high school), Tübingen

* Keplerstraße in Hanau near Frankfurt am Main

* Keplerstraße in Munich, Germany

* Keplerstraße and Keplerbrücke in Graz, Austria

* Keplerplatz, a station on the U1 line of the Vienna U-Bahn rapid transit (Metro) system

Johannes Kepler Grammar School, at the site where Kepler lived in Prague

Kepler Launch Site

Notes and references

The most complete biography of Kepler is Max Caspar's ''Kepler''. Though there are a number of more recent biographies, most are based on Caspar's work with minimal original research; much of the information cited from Caspar can also be found in the books by Arthur Koestler, Kitty Ferguson, and James A. Connor. Owen Gingerich's ''The Eye of Heaven'' builds on Caspar's work to place Kepler in the broader intellectual context of early-modern astronomy. Many later studies have focused on particular elements of his life and work. Kepler's mathematics, cosmological, philosophical and historical views have been extensively analyzed in books and journal articles, though his astrological work—and its relationship to his astronomy—remains understudied.

==Sources==

Andersen, Hanne; Peter Barker; and Xiang Chen. ''The Cognitive Structure of Scientific Revolutions'', chapter 6: "The Copernican Revolution." New York: Cambridge University Press, 2006. ISBN 0-521-85575-6

Armitage, Angus. ''John Kepler'', Faber, 1966.

Banville, John. ''Kepler'', Martin, Secker and Warburg, London, 1981 (fictionalised biography)

Barker, Peter and Bernard R. Goldstein: "Theological Foundations of Kepler's Astronomy". ''Osiris'', Volume 16. ''Science in Theistic Contexts.'' University of Chicago Press, 2001, pp. 88–113

Caspar, Max. ''Kepler''; transl. and ed. by C. Doris Hellman; with a new introduction and references by Owen Gingerich; bibliographic citations by Owen Gingerich and Alain Segonds. New York: Dover, 1993. ISBN 0-486-67605-6

Connor, James A. ''Kepler's Witch: An Astronomer's Discovery of Cosmic Order Amid Religious War, Political Intrigue, and the Heresy Trial of His Mother''. HarperSanFrancisco, 2004. ISBN 0-06-052255-0

De Gandt, Francois. ''Force and Geometry in Newton's'' Principia, Translated by Curtis Wilson, Princeton University Press 1995. ISBN 0-691-03367-6

Dreyer, J. L. E. ''A History of Astronomy from Thales to Kepler''. Dover Publications Inc, 1967. ISBN 0-486-60079-3

Ferguson, Kitty. ''The nobleman and his housedog: Tycho Brahe and Johannes Kepler: the strange partnership that revolutionized science.'' London: Review, 2002. ISBN 0-7472-7022-8 – published in the US as: ''Tycho & Kepler: the unlikely partnership that forever changed our understanding of the heavens.'' New York: Walker, 2002. ISBN 0-8027-1390-4

Field, J. V.. ''Kepler's geometrical cosmology''. Chicago University Press, 1988. ISBN 0-226-24823-2

Gilder, Joshua and Anne-Lee Gilder: ''Heavenly Intrigue: Johannes Kepler, Tycho Brahe, and the Murder Behind One of History's Greatest Scientific Discoveries'', Doubleday (May 18, 2004). ISBN 0-385-50844-1 Reviews bookpage.com, crisismagazine.com

Gingerich, Owen. ''The Eye of Heaven: Ptolemy, Copernicus, Kepler''. American Institute of Physics, 1993. ISBN 0-88318-863-5 (Masters of modern physics; v. 7)

Gingerich, Owen: "Kepler, Johannes" in ''Dictionary of Scientific Biography'', Volume VII. Charles Coulston Gillispie, editor. New York: Charles Scribner's Sons, 1973

Jardine, Nick: "Koyré’s Kepler/Kepler's Koyré," ''History of Science'', Vol. 38 (2000), pp. 363–376

Kepler, Johannes. ''Johannes Kepler New Astronomy'' trans. W. Donahue, forward by O. Gingerich, Cambridge University Press 1993. ISBN 0-521-30131-9

Kepler, Johannes and Christian Frisch. ''Joannis Kepleri Astronomi Opera Omnia'' (''John Kepler, Astronomer; Complete Works''), 8 vols.(1858–1871). vol. 1, 1858, vol. 2, 1859, vol. 3,1860, vol. 6, 1866, vol. 7, 1868, Francofurti a.M. et Erlangae, Heyder & Zimmer, – Google Books

Kepler, Johannes, et al. ''Great Books of the Western World. Volume 16: Ptolemy, Copernicus, Kepler'', Chicago: Encyclopædia Britannica, Inc., 1952. (contains English translations by of Kepler's ''Epitome'', Books IV & V and ''Harmonices'' Book 5)

Koestler, Arthur. ''The Sleepwalkers: A History of Man's Changing Vision of the Universe.'' (1959). ISBN 0-14-019246-8

Koyré, Alexandre: ''Galilean Studies'' Harvester Press 1977. ISBN 0-85527-354-2

Koyré, Alexandre: ''The Astronomical Revolution: Copernicus-Kepler-Borelli'' Ithaca, NY: Cornell University Press, 1973. ISBN 0-8014-0504-1; Methuen, 1973. ISBN 0-416-76980-2; Hermann, 1973. ISBN 2-7056-5648-0

Kuhn, Thomas S. ''The Copernican Revolution: Planetary Astronomy in the Development of Western Thought''. Cambridge, MA: Harvard University Press, 1957. ISBN 0-674-17103-9

Lindberg, David C.: "The Genesis of Kepler's Theory of Light: Light Metaphysics from Plotinus to Kepler." ''Osiris'', N.S. 2. University of Chicago Press, 1986, pp. 5–42.

Lear, John. ''Kepler's Dream''. Berkeley: University of California Press, 1965

North, John. ''The Fontana History of Astronomy and Cosmology,'' Fontana Press, 1994. ISBN 0-00-686177-6

Pannekoek, Anton: ''A History of Astronomy'', Dover Publications Inc 1989. ISBN 0-486-65994-1

Pauli, Wolfgang. ''Wolfgang Pauli — Writings on physics and philosophy'', translated by Robert Schlapp and edited by P. Enz and Karl von Meyenn (Springer Verlag, Berlin, 1994). See section 21, ''The influence of archetypical ideas on the scientific theories of Kepler'', concerning Johannes Kepler and Robert Fludd (1574–1637). ISBN 3-540-56859-X

Schneer, Cecil: "Kepler's New Year's Gift of a Snowflake." ''Isis'', Volume 51, No. 4. University of Chicago Press, 1960, pp. 531–545.

Shapin, Steven. ''The Scientific Revolution''. Chicago: University of Chicago Press, 1996. ISBN 0-226-75020-5

Stephenson, Bruce. ''Kepler's physical astronomy''. New York: Springer, 1987. ISBN 0-387-96541-6 (Studies in the history of mathematics and physical sciences; 13); reprinted Princeton:Princeton Univ. Pr., 1994. ISBN 0-691-03652-7

Stephenson, Bruce. ''The Music of the Heavens: Kepler's Harmonic Astronomy'', Princeton University Press, 1994. ISBN 0-691-03439-7

Toulmin, Stephen and June Goodfield. ''The Fabric of the Heavens: The Development of Astronomy and Dynamics''. Pelican, 1963.

Voelkel, James R. ''The Composition of Kepler's Astronomia nova'', Princeton University Press, 2001. ISBN 0-691-00738-1

Westfall, Richard S.. ''The Construction of Modern Science: Mechanism and Mechanics''. John Wiley and Sons, 1971. ISBN 0-471-93531-X; reprinted Cambridge University Press, 1978. ISBN 0-521-29295-6

Westfall, Richard S. ''Never at Rest: A Biography of Isaac Newton''. Cambridge University Press, 1981. ISBN 0-521-23143-4

Wolf, A. ''A History of Science, Technology and Philosophy in the 16th and 17th centuries''. George Allen & Unwin, 1950.

External links

JohannesKepler.Info Kepler information and community website, launched on December 27, 2009

''Harmonices mundi'' ("The Harmony of the Worlds") in fulltext facsimile; Carnegie-Mellon University

''De Stella Nova in Pede Serpentarii'' ("On the new star in Ophiuchus's foot") in full text facsimile at Linda Hall Library

(1920 book, part of ''Men of Science'' series)

Electronic facsimile-editions of the rare book collection at the Vienna Institute of Astronomy

Audio – Cain/Gay (2010) Astronomy Cast Johannes Kepler and His Laws of Planetary Motion

Christianson, Gale E., Kepler's Somnium: Science Fiction and the Renaissance Scientist

Kollerstrom, Nicholas, Kepler's Belief in Astrology

References for Johannes Kepler

Plant, David, Kepler and the "Music of the Spheres"

Kepler, Napier, and the Third Law at MathPages

Calderón Urreiztieta, Carlos. Harmonice Mundi • Animated and multimedia version of Book V

Reading the mind of God 1997 drama based on his life by Patrick Gabridge

Johannes Kepler 2010 drama based on his life by Robert Lalonde

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Coordinates	12°2′36″N77°1′42″N
name	Carl Sagan
birth date	November 09, 1934
birth place	Brooklyn, New York City, U.S.
residence	United States
nationality	American
death date	December 20, 1996
death place	Seattle, Washington, U.S.
death cause	Pneumonia
education	Rahway High School
alma mater	University of Chicago,Cornell University
field	Astronomy, Astrophysics, Cosmology, Astrobiology, Space science, Planetary science
work institutions	Cornell University Harvard University Smithsonian Astrophysical Observatory University of California, Berkeley
alma mater	University of Chicago (B.A.), (B.Sc.), (M.Sc.), (Ph.D.)
known for	Search for Extra-Terrestrial Intelligence (SETI) ''Cosmos: A Personal Voyage'' ''Cosmos'' Voyager Golden Record Pioneer plaque ''Contact'' ''Pale Blue Dot''
prizes	Oersted Medal (1990) NASA Distinguished Public Service Medal (twice) Pulitzer Prize for General Non-Fiction (1978) National Academy of Sciences Public Welfare Medal (1994) }}

Carl Edward Sagan () (November 9, 1934 December 20, 1996) was an American astronomer, astrophysicist, cosmologist, author, science popularizer, and science communicator in the space and natural sciences. During his lifetime, he published more than 600 scientific papers and popular articles and was author, co-author, or editor of more than 20 books. In his works, he advocated skeptical inquiry and the scientific method. He pioneered exobiology and promoted the Search for Extra-Terrestrial Intelligence (SETI).

Sagan became world-famous for his popular science books and for the award-winning 1980 television series ''Cosmos: A Personal Voyage'', which he narrated and co-wrote. A book to accompany the program was also published. Sagan also wrote the novel ''Contact'', the basis for the 1997 film of the same name.

Early life

Carl Sagan was born in Brooklyn, New York City, to a Ukrainian Jewish family. His father, Sam Sagan, was an immigrant garment worker from Kamenets-Podolsk, Ukraine; his mother, Rachel Molly Gruber, a housewife. Carl was named in honor of Rachel's biological mother, Chaiya Clara, in Sagan's words, "the mother she never knew." Sagan graduated from Rahway High School in Rahway, New Jersey, in 1951.

He had one sister, Carol, and the family lived in a modest apartment near the Atlantic Ocean, in Bensonhurst, a Brooklyn neighborhood. According to Sagan, they were Reform Jews, the most liberal of the three main Jewish groups. Both Sagan and his sister agree that their father was not especially religious, but that their mother "definitely believed in God, and was active in the temple ... and served only Kosher meat." During the height of the Depression, his father had to accept a job as a theater usher.

According to biographer Keay Davidson, Sagan's "inner war" was a result of his close relations with both his parents, who were in many ways "opposites." Sagan traced his later analytical urges to his mother, a woman who had known "extreme poverty as a child," and had grown up almost homeless in New York City during World War I and the 1920s. She had her own intellectual ambitions as a young woman, but they were blocked by social restrictions, because of her poverty, her being a woman and wife, and her Jewish religion. Davidson notes that she therefore "worshiped her only son, Carl. He would fulfill her unfulfilled dreams."

However, his "sense of wonder" came from his father, who was a "quiet and soft-hearted escapee from the Czar." In his free time, he gave apples to the poor, or helped soothe labor-management tensions within New York's "tumultuous" garment industry. Although he was "awed" by Carl's "brilliance, his boyish chatter about stars and dinosaurs," he took his son's inquisitiveness in stride, as part of his growing up. In his later years as a writer and scientist, Sagan would often draw on his childhood memories to illustrate scientific points, as he did in his book, ''Shadows of Forgotten Ancestors''. Sagan describes his parents' influence on his later thinking:

:''My parents were not scientists. They knew almost nothing about science. But in introducing me simultaneously to skepticism and to wonder, they taught me the two uneasily cohabiting modes of thought that are central to the scientific method.''

1939 World's Fair

Sagan recalls that one of his best experiences was when he was four or five years old, his parents took him to the 1939 New York World's Fair. The exhibits became a turning point in his life. He later recalled the moving map of the "America of Tomorrow" exhibit: "It showed beautiful highways and cloverleaves and little General Motors cars all carrying people to skyscrapers, buildings with lovely spires, flying buttresses — and it looked great!" At other exhibits, he remembered how a flashlight that shined on a photoelectric cell created a cracking sound, and how the sound from a tuning fork became a wave on an oscilloscope. He also witnessed the future media technology that would replace radio: television. Sagan wrote:

:''Plainly, the world held wonders of a kind I had never guessed. How could a tone become a picture and light become a noise?''

He also saw one of the Fair's most publicized events, the burial of a time capsule at Flushing Meadows, which contained mementos of the 1930s to be recovered by Earth's descendants in a future millennium. "The time capsule thrilled Carl," writes Davidson. As an adult, Sagan and his colleagues created similar time capsules, but ones that would be sent out into the galaxy. These were the Pioneer plaque and the ''Voyager Golden Record'' records, all of which were spinoffs of Sagan's memories of the World Fair.

World War II

During World War II, Sagan's family worried about the fate of their European relatives. Sagan, however, was generally unaware of the details of the ongoing war. He writes, "Sure, we had relatives who were caught up in the Holocaust. Hitler was not a popular fellow in our household ... But on the other hand, I was fairly insulated from the horrors of the war." His sister, Carol, said that their mother "above all wanted to protect Carl ... She had an extraordinarily difficult time dealing with World War II and the Holocaust." Sagan's book, ''The Demon-Haunted World'' (1996), included his memories of this conflicted period in his life, where his family dealt with the realities of the war in Europe, but tried to prevent it from undermining his optimistic spirit.

Inquisitiveness about nature

Soon after entering elementary school, he began to express a strong inquisitiveness about nature. Sagan recalled taking his first trips to the public library alone, at the age of five, when his mother got him a library card. He wanted to learn what stars were, since none of his friends or their parents could give him a clear answer: :''I went to the librarian and asked for a book about stars ... And the answer was stunning. It was that the Sun was a star but really close. The stars were suns, but so far away they were just little points of light ... The scale of the universe suddenly opened up to me. It was a kind of religious experience. There was a magnificence to it, a grandeur, a scale which has never left me. Never ever left me.''

About the time he was six or seven, he and a close friend took trips to the American Museum of Natural History in New York City. While there, they went to the Hayden Planetarium and walked around the museum's exhibits of space objects, such as meteorites, and displays of dinosaurs and animals in natural settings. Sagan writes about those visits: :''I was transfixed by the dioramas — lifelike representations of animals and their habitats all over the world. Penguins on the dimly lit Antarctic ice; ... a family of gorillas, the male beating his chest, ... an American grizzly bear standing on his hind legs, ten or twelve feet tall, and staring me right in the eye.''

His parents helped nurture his growing interest in science by buying him chemistry sets and reading materials. His interest in space, however, was his primary focus, especially after reading science fiction stories by writers such as Edgar Rice Burroughs, which stirred his imagination about life on other planets, such as Mars. According to biographer Ray Spangenburg, these early years as Sagan tried to understand the mysteries of the planets, became a "driving force in his life, a continual spark to his intellect, and a quest that would never be forgotten."

Education and scientific career

He attended the University of Chicago, where he participated in the Ryerson Astronomical Society, received a bachelor of arts with general and special honors in 1954, a bachelor of science in 1955, and a master of science in physics in 1956 before earning a PhD in astronomy and astrophysics in 1960. During his time as an undergraduate, Sagan worked in the laboratory of the geneticist H. J. Muller. From 1960 to 1962 Sagan was a Miller Fellow at the University of California, Berkeley. From 1962 to 1968, he worked at the Smithsonian Astrophysical Observatory in Cambridge, Massachusetts.

Sagan lectured and did research at Harvard University until 1968, when he moved to Cornell University in Ithaca, New York. He became a full Professor at Cornell in 1971, and he directed the Laboratory for Planetary Studies there. From 1972 to 1981, Sagan was the Associate Director of the Center for Radio Physics and Space Research at Cornell.

Sagan was associated with the American space program from its inception. From the 1950s onward, he worked as an advisor to NASA, where one of his duties included briefing the Apollo astronauts before their flights to the Moon. Sagan contributed to many of the robotic spacecraft missions that explored the solar system, arranging experiments on many of the expeditions. He conceived the idea of adding an unalterable and universal message on spacecraft destined to leave the solar system that could potentially be understood by any extraterrestrial intelligence that might find it. Sagan assembled the first physical message that was sent into space: a gold-anodized plaque, attached to the space probe Pioneer 10, launched in 1972. Pioneer 11, also carrying another copy of the plaque, was launched the following year. He continued to refine his designs; the most elaborate message he helped to develop and assemble was the Voyager Golden Record that was sent out with the Voyager space probes in 1977. Sagan often challenged the decisions to fund the Space Shuttle and Space Station at the expense of further robotic missions.

Sagan taught a course on critical thinking at Cornell University until he died in 1996 from pneumonia, a few months after finding that he was in remission of myelodysplastic syndrome.

Scientific achievements

Sagan's contributions were central to the discovery of the high surface temperatures of the planet Venus. In the early 1960s no one knew for certain the basic conditions of that planet's surface, and Sagan listed the possibilities in a report later depicted for popularization in a Time-Life book, ''Planets''. His own view was that Venus was dry and very hot as opposed to the balmy paradise others had imagined. He had investigated radio emissions from Venus and concluded that there was a surface temperature of . As a visiting scientist to NASA's Jet Propulsion Laboratory, he contributed to the first Mariner missions to Venus, working on the design and management of the project. Mariner 2 confirmed his conclusions on the surface conditions of Venus in 1962.

Sagan was among the first to hypothesize that Saturn's moon Titan might possess oceans of liquid compounds on its surface and that Jupiter's moon Europa might possess subsurface oceans of water. This would make Europa potentially habitable for life. Europa's subsurface ocean of water was later indirectly confirmed by the spacecraft Galileo. Sagan also helped solve the mystery of the reddish haze seen on Titan, revealing that it is composed of complex organic molecules constantly raining down onto the moon's surface.

He further contributed insights regarding the atmospheres of Venus and Jupiter as well as seasonal changes on Mars. Sagan established that the atmosphere of Venus is extremely hot and dense with pressures increasing steadily all the way down to the surface. He also perceived global warming as a growing, man-made danger and likened it to the natural development of Venus into a hot, life-hostile planet through a kind of runaway greenhouse effect. Sagan and his Cornell colleague Edwin Ernest Salpeter speculated about life in Jupiter's clouds, given the planet's dense atmospheric composition rich in organic molecules. He studied the observed color variations on Mars' surface and concluded that they were not seasonal or vegetational changes as most believed but shifts in surface dust caused by windstorms.

Sagan is best known, however, for his research on the possibilities of extraterrestrial life, including experimental demonstration of the production of amino acids from basic chemicals by radiation.

He is also the 1994 recipient of the Public Welfare Medal, the highest award of the National Academy of Sciences for "distinguished contributions in the application of science to the public welfare." He was denied membership in the Academy, reportedly because his media activities made him unpopular with many other scientists.

Sagan's ability to convey his ideas allowed many people to better understand the cosmos — simultaneously emphasizing the value and worthiness of the human race, and the relative insignificance of the Earth in comparison to the universe. He delivered the 1977 series of Royal Institution Christmas Lectures in London. He hosted and, with Ann Druyan, co-wrote and co-produced the highly popular thirteen-part PBS television series ''Cosmos: A Personal Voyage'' modeled on Jacob Bronowski's ''The Ascent of Man''.

Sagan was a proponent of the search for extraterrestrial life. He urged the scientific community to listen with radio telescopes for signals from intelligent extraterrestrial life-forms. So persuasive was he that by 1982 he was able to get a petition advocating SETI published in the journal ''Science'' and signed by 70 scientists including seven Nobel Prize winners. This was a tremendous turnaround in the respectability of this controversial field. Sagan also helped Dr. Frank Drake write the Arecibo message, a radio message beamed into space from the Arecibo radio telescope on November 16, 1974, aimed at informing extraterrestrials about Earth.

Sagan was chief technology officer of the professional planetary research journal ''Icarus'' for twelve years. He co-founded the ''Planetary Society'', the largest space-interest group in the world, with over 100,000 members in more than 149 countries, and was a member of the SETI Institute Board of Trustees. Sagan served as Chairman of the Division for Planetary Science of the American Astronomical Society, as President of the Planetology Section of the American Geophysical Union, and as Chairman of the Astronomy Section of the American Association for the Advancement of Science.

At the height of the Cold War, Sagan became involved in public awareness efforts for the effects of nuclear war when a mathematical climate model suggested that a substantial nuclear exchange could upset the delicate balance of life on Earth. He was one of five authors — the "S" of the "TTAPS" report as the research paper came to be known. He eventually co-authored the scientific paper hypothesizing a global nuclear winter following nuclear war. He also co-authored the book ''A Path Where No Man Thought: Nuclear Winter and the End of the Arms Race'', a comprehensive examination of the phenomenon of nuclear winter.

''Cosmos'' covered a wide range of scientific subjects including the origin of life and a perspective of our place in the universe. The series was first broadcast by the Public Broadcasting Service in 1980, winning an Emmy and a Peabody Award. It has been broadcast in more than 60 countries and seen by over 500 million people, making it the most widely watched PBS program in history. In addition, ''Time'' magazine ran a cover story about Sagan soon after the show broadcast, referring to him as "creator, chief writer and host-narrator of the new public television series Cosmos, [and] takes the controls of his fantasy spaceship."

Sagan also wrote books to popularize science, such as ''Cosmos'', which reflected and expanded upon some of the themes of ''A Personal Voyage'', and became the best-selling science book ever published in English; ''The Dragons of Eden: Speculations on the Evolution of Human Intelligence'', which won a Pulitzer Prize; and ''Broca's Brain: Reflections on the Romance of Science''. Sagan also wrote the best-selling science fiction novel ''Contact'' in 1985, based on a film treatment he wrote with his wife in 1979, but he did not live to see the book's 1997 motion picture adaptation, which starred Jodie Foster and won the 1998 Hugo Award for Best Dramatic Adaption.

thumb|left|Pale Blue Dot: Earth is a bright pixel when photographed from "Voyager 1" six billion kilometers out (past Pluto). Sagan encouraged NASA to generate this image. He wrote a sequel to ''Cosmos,'' ''Pale Blue Dot: A Vision of the Human Future in Space'', which was selected as a notable book of 1995 by ''The New York Times''. He appeared on PBS' Charlie Rose program in January 1995. Sagan also wrote an introduction for the bestselling book by Stephen Hawking, ''A Brief History of Time''. Sagan was also known for his popularization of science, his efforts to increase scientific understanding among the general public, and his positions in favor of scientific skepticism and against pseudoscience, such as his debunking of the Betty and Barney Hill abduction. To mark the tenth anniversary of Sagan's passing, David Morrison, a former student of Sagan, recalled "Sagan's immense contributions to planetary research, the public understanding of science, and the skeptical movement" in ''Skeptical Inquirer''.

Sagan hypothesized in January 1991 that enough smoke from the 1991 Kuwaiti oil fires "might get so high as to disrupt agriculture in much of South Asia ..." He later conceded in ''The Demon-Haunted World'' that this prediction did not turn out to be correct: "it ''was'' pitch black at noon and temperatures dropped 4°–6°C over the Persian Gulf, but not much smoke reached stratospheric altitudes and Asia was spared." A 2007 study noted that modern computer models have been applied to the Kuwait oil fires, finding that individual smoke plumes are not able to loft smoke into the stratosphere, but that smoke from fires covering a large area, like some forest fires or the burning of cities that would be expected to follow a nuclear strike, would loft significant amounts of smoke into the stratosphere.

In his later years Sagan advocated the creation of an organized search for near Earth objects that might impact the Earth. When others suggested creating large nuclear bombs that could be used to alter the orbit of a NEO that was predicted to hit the Earth, Sagan proposed the Deflection Dilemma: If we create the ability to deflect an asteroid away from the Earth, then we also create the ability to deflect an asteroid towards the Earth — providing an evil power with a true doomsday bomb.

Billions and billions

From ''Cosmos'' and his frequent appearances on ''The Tonight Show Starring Johnny Carson'', Sagan became associated with the catchphrase "billions and billions". Sagan stated that he never actually used the phrase in the ''Cosmos'' series. The closest that he ever came was in the book ''Cosmos'', where he talked of "billions ''upon'' billions": }}

However, his frequent use of the word ''billions'', and distinctive delivery emphasizing the "b" (which he did intentionally, in place of more cumbersome alternatives such as "billions with a 'b'", in order to distinguish the word from "millions" in viewers' minds), made him a favorite target of comic performers, including Johnny Carson, Gary Kroeger, Mike Myers, Bronson Pinchot, Penn Jillette, Harry Shearer, and others. Frank Zappa satirized the line in the song "Be In My Video", noting as well "atomic light". Sagan took this all in good humor, and his final book was entitled ''Billions and Billions'' which opened with a tongue-in-cheek discussion of this catchphrase, observing that Carson himself was an amateur astronomer and that Carson's comic caricature often included real science.

The popular perception of his characterization of large cosmic quantities continued to be a sense of wonderment at the vastness of space and time, as in his phrase "The total number of stars in the Universe is larger than all the grains of sand on all the beaches of the planet Earth." However, this famous saying was widely misunderstood, as he was in fact referring to the world being at a "critical branch point in history" as in the following quote from ''Cosmos: A Personal Voyage'', Episode 8: "Journeys in Space and Time":

"Those worlds in space are as countless as all the grains of sand on all the beaches of the earth. Each of those worlds is as real as ours and every one of them is a succession of incidents, events, occurrences which influence its future. Countless worlds, numberless moments, an immensity of space and time. And our small planet at this moment, here we face a critical branch point in history: what we do with our world, right now, will propagate down through the centuries and powerfully affect the destiny of our descendants. It is well within our power to destroy our civilization and perhaps our species as well."

Sagan units

As a humorous tribute to him, a ''sagan'' has been defined as a unit of measurement equal to at least four billion, since the lower bound of a number conforming to the constraint of ''billions and billions'' must be two billion plus two billion.

Social concerns

Sagan believed that the Drake equation, on substitution of reasonable estimates, suggested that a large number of extraterrestrial civilizations would form, but that the lack of evidence of such civilizations highlighted by the Fermi paradox suggests technological civilizations tend to destroy themselves rather quickly. This stimulated his interest in identifying and publicizing ways that humanity could destroy itself, with the hope of avoiding such a cataclysm and eventually becoming a spacefaring species. Sagan's deep concern regarding the potential destruction of human civilization in a nuclear holocaust was conveyed in a memorable cinematic sequence in the final episode of ''Cosmos'', called "Who Speaks for Earth?" Sagan had already resigned from the Air Force Scientific Advisory Board and voluntarily surrendered his top secret clearance in protest over the Vietnam War. Following his marriage to his third wife (novelist Ann Druyan) in June 1981, Sagan became more politically active — particularly in opposing escalation of the nuclear arms race under President Ronald Reagan.

In March 1983, Reagan announced the Strategic Defense Initiative — a multi-billion dollar project to develop a comprehensive defense against attack by nuclear missiles, which was quickly dubbed the "Star Wars" program. Sagan spoke out against the project, arguing that it was technically impossible to develop a system with the level of perfection required, and far more expensive to build than for an enemy to defeat through decoys and other means — and that its construction would seriously destabilize the nuclear balance between the United States and the Soviet Union, making further progress toward nuclear disarmament impossible.

When Soviet leader Mikhail Gorbachev declared a unilateral moratorium on the testing of nuclear weapons, which would begin on August 6, 1985 — the 40th anniversary of the atomic bombing of Hiroshima — the Reagan administration dismissed the dramatic move as nothing more than propaganda, and refused to follow suit. In response, American anti-nuclear and peace activists staged a series of protest actions at the Nevada Test Site, beginning on Easter Sunday in 1986 and continuing through 1987. Hundreds of people were arrested, including Sagan, who was arrested on two separate occasions as he climbed over a chain-link fence at the test site.

Personal life and beliefs

Sagan was married three times — in 1957, to biologist Lynn Margulis, mother of Dorion Sagan and Jeremy Sagan; in 1968, to artist Linda Salzman, mother of Nick Sagan; and in 1981, to author Ann Druyan, mother of Alexandra Rachel (Sasha) Sagan and Samuel Democritus Sagan. His marriage to Druyan continued until his death in 1996.

Isaac Asimov described Sagan as one of only two people he ever met whose intellect surpassed his own. The other, he claimed, was the computer scientist and artificial intelligence expert Marvin Minsky.

Sagan wrote frequently about religion and the relationship between religion and science, expressing his skepticism about the conventional conceptualization of God as a sapient being. For example:

Some people think God is an outsized, light-skinned male with a long white beard, sitting on a throne somewhere up there in the sky, busily tallying the fall of every sparrow. Others — for example Baruch Spinoza and Albert Einstein — considered God to be essentially the sum total of the physical laws which describe the universe. I do not know of any compelling evidence for anthropomorphic patriarchs controlling human destiny from some hidden celestial vantage point, but it would be madness to deny the existence of physical laws.

In another description of his view of God, Sagan emphatically writes:

The idea that God is an oversized white male with a flowing beard who sits in the sky and tallies the fall of every sparrow is ludicrous. But if by God one means the set of physical laws that govern the universe, then clearly there is such a God. This God is emotionally unsatisfying... it does not make much sense to pray to the law of gravity.

Despite his criticism of religion, Sagan denied that he was an atheist, saying "An atheist has to know a lot more than I know. An atheist is someone who knows there is no god. By some definitions atheism is very stupid." In reply to a question in 1996 about his religious beliefs, Sagan answered, "I'm agnostic." Sagan maintained that the idea of a creator of the universe was difficult to prove or disprove and that the only conceivable scientific discovery that could challenge it would be an infinitely old universe. According to his last wife, Ann Druyan, he was not a believer: }}

In 2006, Ann Druyan edited Sagan's 1985 Glasgow ''Gifford Lectures in Natural Theology'' into a book, ''The Varieties of Scientific Experience: A Personal View of the Search for God'', in which he elaborates on his views of divinity in the natural world. Sagan is also widely regarded as a freethinker or skeptic; one of his most famous quotations, in ''Cosmos'', was, "Extraordinary claims require extraordinary evidence" (called the "Sagan Standard" by some). This was based on a nearly identical statement by fellow founder of the Committee for the Scientific Investigation of Claims of the Paranormal, Marcello Truzzi, "An extraordinary claim requires extraordinary proof." This idea originated with Pierre-Simon Laplace (1749–1827), a French mathematician and astronomer who said, "The weight of evidence for an extraordinary claim must be proportioned to its strangeness."

Late in his life, Sagan's books elaborated on his skeptical, naturalistic view of the world. In ''The Demon-Haunted World: Science as a Candle in the Dark'', he presented tools for testing arguments and detecting fallacious or fraudulent ones, essentially advocating wide use of critical thinking and the scientific method. The compilation ''Billions and Billions: Thoughts on Life and Death at the Brink of the Millennium'', published in 1997 after Sagan's death, contains essays written by Sagan, such as his views on abortion, and his widow Ann Druyan's account of his death as a skeptic, agnostic, and freethinker.

Sagan warned against humans' tendency towards anthropocentrism. He was the faculty adviser for the Cornell Students for the Ethical Treatment of Animals. In the ''Cosmos'' chapter "Blues For a Red Planet", Sagan wrote, "If there is life on Mars, I believe we should do nothing with Mars. Mars then belongs to the Martians, even if the Martians are only microbes."

Sagan was a user and advocate of marijuana. Under the pseudonym "Mr. X", he contributed an essay about smoking cannabis to the 1971 book ''Marihuana Reconsidered''. The essay explained that marijuana use had helped to inspire some of Sagan's works and enhance sensual and intellectual experiences. After Sagan's death, his friend Lester Grinspoon disclosed this information to Sagan's biographer, Keay Davidson. The publishing of the biography, ''Carl Sagan: A Life'', in 1999 brought media attention to this aspect of Sagan's life. Not long after his death, widow Ann Druyan had gone on to preside over the board of directors of NORML, a foundation dedicated to reforming cannabis laws.

In 1994, engineers at Apple Computer code-named the Power Macintosh 7100 "Carl Sagan" in the hope that Apple would make "billions and billions" with the sale of the PowerMac 7100. The name was only used internally, but Sagan was concerned that it would become a product endorsement and sent Apple a cease and desist letter. Apple complied, but engineers retaliated by changing the internal codename to "BHA" for "Butt-Head Astronomer". Sagan then sued Apple for libel, a form of defamation, in federal court. The court granted Apple's motion to dismiss Sagan's claims and opined in dicta that a reader aware of the context would understand Apple was "clearly attempting to retaliate in a humorous and satirical way", and that "It strains reason to conclude that Defendant was attempting to criticize Plaintiff's reputation or competency as an astronomer. One does not seriously attack the expertise of a scientist using the undefined phrase 'butt-head'." Sagan then sued for Apple's original use of his name and likeness, but again lost. Sagan appealed the ruling. In November 1995, an out of court settlement was reached and Apple's office of trademarks and patents released a conciliatory statement that "Apple has always had great respect for Dr. Sagan. It was never Apple's intention to cause Dr. Sagan or his family any embarrassment or concern."

Sagan briefly served as an adviser on Stanley Kubrick's film ''2001: A Space Odyssey''. Sagan proposed that the film would suggest, rather than depict, extraterrestrial superintelligence.

Sagan and UFOs

Sagan had some interest in UFO reports from at least 1964 when he had several conversations on the subject with Jacques Vallee. Though quite skeptical of any extraordinary answer to the UFO question, Sagan thought scientists should study the phenomenon, at least because there was widespread public interest in UFO reports.

Stuart Appelle notes that Sagan "wrote frequently on what he perceived as the logical and empirical fallacies regarding UFOs and the abduction experience. Sagan rejected an extraterrestrial explanation for the phenomenon but felt there were both empirical and pedagogical benefits for examining UFO reports and that the subject was, therefore, a legitimate topic of study."

In 1966, Sagan was a member of the Ad Hoc Committee to Review Project Blue Book, the U.S. Air Force's UFO investigation project. The committee concluded Blue Book had been lacking as a scientific study, and recommended a university-based project to give the UFO phenomenon closer scientific scrutiny. The result was the Condon Committee (1966–1968), led by physicist Edward Condon, and in their final report they formally concluded that UFOs, regardless of what any of them actually were, did not behave in a manner consistent with a threat to national security.

Ron Westrum writes that "The high point of Sagan's treatment of the UFO question was the AAAS's symposium in 1969. A wide range of educated opinions on the subject were offered by participants, including not only proponents such as James McDonald and J. Allen Hynek but also skeptics like astronomers William Hartmann and Donald Menzel. The roster of speakers was balanced, and it is to Sagan's credit that this event was presented in spite of pressure from Edward Condon". With physicist Thornton Page, Sagan edited the lectures and discussions given at the symposium; these were published in 1972 as ''UFOs: A Scientific Debate''. Some of Sagan's many books examine UFOs (as did one episode of ''Cosmos'') and he claimed a religious undercurrent to the phenomenon.

Sagan again revealed his views on interstellar travel in his 1980 ''Cosmos'' series. In one of his last written works, Sagan argued that the chances of extraterrestrial spacecraft visiting Earth are vanishingly small. However, Sagan did think it plausible that Cold War concerns contributed to governments misleading their citizens about UFOs, and that "some UFO reports and analyses, and perhaps voluminous files, have been made inaccessible to the public which pays the bills ... It's time for the files to be declassified and made generally available." He cautioned against jumping to conclusions about suppressed UFO data and stressed that there was no strong evidence that aliens were visiting the Earth either in the past or present.

Death

After a long and difficult fight with myelodysplasia, which included three bone marrow transplants, Sagan died of pneumonia at the age of 62 at the Fred Hutchinson Cancer Research Center in Seattle, Washington, on December 20, 1996. He was buried at Lakeview Cemetery in Ithaca, New York.

Posthumous recognition

The 1997 movie ''Contact'', based on Sagan's novel of the same name and finished after his death, ends with the dedication "For Carl".

In 1997, the Sagan Planet Walk was opened in Ithaca New York. It is a walking scale model of the solar system, extending 1.2 km from the center of The Commons in downtown Ithaca, NY, to the Sciencenter, a hands-on museum. The exhibition was created in memory of Carl Sagan, who was an Ithaca resident and Cornell Professor. Professor Sagan had been a founding member of the museum's advisory board.

The landing site of the unmanned Mars Pathfinder spacecraft was renamed the ''Carl Sagan Memorial Station'' on July 5, 1997.

Sagan's son, Nick Sagan, wrote several episodes in the ''Star Trek'' franchise. In an episode of ''Star Trek: Enterprise'' entitled "Terra Prime", a quick shot is shown of the relic rover Sojourner, part of the Mars Pathfinder mission, placed by a historical marker at Carl Sagan Memorial Station on the Martian surface. The marker displays a quote from Sagan: "Whatever the reason you're on Mars, I'm glad you're there, and I wish I was with you." Sagan's student Steve Squyres led the team that landed the Spirit Rover and Opportunity Rover successfully on Mars in 2004.

Asteroid 2709 Sagan is also named in his honor.

On November 9, 2001, on what would have been Sagan's 67th birthday, the NASA Ames Research Center dedicated the site for the Carl Sagan Center for the Study of Life in the Cosmos. "Carl was an incredible visionary, and now his legacy can be preserved and advanced by a 21st century research and education laboratory committed to enhancing our understanding of life in the universe and furthering the cause of space exploration for all time", said NASA Administrator Daniel Goldin. Ann Druyan was at the Center as it opened its doors on October 22, 2006.

Sagan has at least three awards named in his honor:

The Carl Sagan Memorial Award presented jointly since 1997 by the American Astronomical Society (AAS) and the Planetary Society,

The Carl Sagan Medal for Excellence in Public Communication in Planetary Science presented since 1998 by the American Astronomical Society's Division for Planetary Sciences (AAS/DPS) for outstanding communication by an active planetary scientist to the general public — Carl Sagan was one of the original organizing committee members of the DPS, and

The Carl Sagan Award for Public Understanding of Science presented by the Council of Scientific Society Presidents (CSSP) — Sagan himself was the first recipient of the CSSP award in 1993. In 2006, the Carl Sagan Medal was awarded to astrobiologist and author David Grinspoon, the son of Sagan's friend Lester Grinspoon.

On December 20, 2006, the tenth anniversary of Sagan's death, a blogger, Joel Schlosberg, organized a Carl Sagan "blog-a-thon" to commemorate Sagan's death, and the idea was supported by Nick Sagan. Many members of the blogging community participated.

August 2007 the Independent Investigative Group IIG awarded Sagan posthumously a Lifetime Achievement Award. This honor has also been awarded to Harry Houdini and James Randi.

In 2008, Benn Jordan, also known as "The Flashbulb", released the album ''Pale Blue Dot: A Tribute to Carl Sagan''.

In 2009, clips from Carl Sagan's ''Cosmos'' were used as the basis for ''A Glorious Dawn'', the first video produced for the Symphony of Science, an educational music video production by composer John Boswell. Musician Jack White later released this song as a vinyl single under his record label Third Man Records. Additional clips were used in several followup videos which featured Sagan alongside other noted scientists and proponents of rational thinking, such as Richard Dawkins, Richard Feynman, Brian Greene, Lawrence M. Krauss, Bill Nye, and Neil deGrasse Tyson.

In 2010, the 76th anniversary of Carl Sagan's birth, the second "Carl Sagan Day" was celebrated on November 6.

Awards and honors

Annual Award for Television Excellence — 1981 — The Ohio State University — PBS series ''Cosmos''

Apollo Achievement Award — National Aeronautics and Space Administration

NASA Distinguished Public Service Medal — National Aeronautics and Space Administration (twice)

Emmy — Outstanding Individual Achievement — 1981 — PBS series ''Cosmos''

Emmy — Outstanding Informational Series — 1981 — PBS series ''Cosmos''

Exceptional Scientific Achievement Medal — National Aeronautics and Space Administration

Helen Caldicott Leadership Award — Women's Action for Nuclear Disarmament

Hugo Award — 1981 — ''Cosmos''

Humanist of the Year — 1981 — Awarded by the American Humanist Association

In Praise of Reason Award — 1987 — Committee for the Scientific Investigation of Claims of the Paranormal

Isaac Asimov Award — 1994 — Committee for the Scientific Investigation of Claims of the Paranormal

John F. Kennedy Astronautics Award — American Astronautical Society

John W. Campbell Memorial Award — 1974 — ''Cosmic Connection: An Extraterrestrial Perspective''

Joseph Priestley Award — "For distinguished contributions to the welfare of mankind"

Klumpke-Roberts Award of the Astronomical Society of the Pacific — 1974

Konstantin Tsiolkovsky Medal — Awarded by the Soviet Cosmonauts Federation

Locus Award 1986 — ''Contact''

Lowell Thomas Award — Explorers Club — 75th Anniversary

Masursky Award — American Astronomical Society

Miller Research Fellowship — Miller Institute (1960–1962)

Oersted Medal — 1990 — American Association of Physics Teachers

Peabody Award — 1980 — PBS series ''Cosmos''

Prix Galbert — The international prize of Astronautics

Public Welfare Medal — 1994 — National Academy of Sciences

Pulitzer Prize for General Non-Fiction — 1978 — ''The Dragons of Eden''

SF Chronicle Award — 1998 — ''Contact''

Named the "99th Greatest American" on the June 5, 2005, ''Greatest American'' show on the Discovery Channel

Publications

''Planets'' (LIFE Science Library), Sagan, Carl, Jonathan Norton Leonard and editors of Life, Time, Inc., 1966

''Intelligent Life in the Universe'', I.S. Shklovskii coauthor, Random House, 1966, ISBN 1-892803-02-X, 509 pgs (note: republished in 1998 by Emerson-Adams Press)

''UFOs: A Scientific Debate'', Thornton Page coauthor, Cornell University Press, 1972, 310 pgs

''Communication with Extraterrestrial Intelligence''. MIT Press, 1973, 428 pgs

''Mars and the Mind of Man'', Sagan, Carl, et al., Harper & Row, 1973, 143 pgs

''Cosmic Connection: An Extraterrestrial Perspective'', Jerome Agel coauthor, Anchor Press, 1973, ISBN 0-521-78303-8, 301 pgs

''Other Worlds''. Bantam Books, 1975

''Murmurs of Earth: The Voyager Interstellar Record'', Sagan, Carl, et al., Random House, ISBN 0-394-41047-5, 1978

''The Dragons of Eden: Speculations on the Evolution of Human Intelligence''. Ballantine Books, 1978, ISBN 0-345-34629-7, 288 pgs

''Broca's Brain: Reflections on the Romance of Science''. Ballantine Books, 1979, ISBN 0-345-33689-5, 416 pgs

''Cosmos''. Random house, 1980. Random House New Edition, May 7, 2002, ISBN 0-375-50832-5, 384 pgs

''The Cold and the Dark: The World after Nuclear War'', Sagan, Carl et al., Sidgwick & Jackson, 1985

''Comet'', Ann Druyan coauthor, Ballantine Books, 1985, ISBN 0-345-41222-2, 496 pgs

''Contact''. Simon and Schuster, 1985; Reissued August 1997 by Doubleday Books, ISBN 1-56865-424-3, 352 pgs

''A Path Where No Man Thought: Nuclear Winter and the End of the Arms Race'', Richard Turco coauthor, Random House, 1990, ISBN 0-394-58307-8, 499 pgs

''Shadows of Forgotten Ancestors: A Search for Who We Are'', Ann Druyan coauthor, Ballantine Books, October 1993, ISBN 0-345-38472-5, 528 pgs

''Pale Blue Dot: A Vision of the Human Future in Space''. Random House, November 1994, ISBN 0-679-43841-6, 429 pgs

''The Demon-Haunted World: Science as a Candle in the Dark''. Ballantine Books, March 1996, ISBN 0-345-40946-9, 480 pgs (note: the book was first published and copyrighted in 1995 with an errata slip inserted)

''Billions and Billions: Thoughts on Life and Death at the Brink of the Millennium'', Ann Druyan coauthor, Ballantine Books, June 1997, ISBN 0-345-37918-7, 320 pgs

''The Varieties of Scientific Experience: A Personal View of the Search for God'', Carl Sagan (writer) & Ann Druyan (editor), 1985 Gifford lectures, Penguin Press HC, November 2006, ISBN 1-59420-107-2, 304 pgs

References

Further reading

External links

The Carl Sagan Portal

BBC Radio program "Great Lives" on Carl Sagan's life

A Man whose time Has come — Interview with Carl Sagan by Ian Ridpath, New Scientist 1974 July 4

Carl Sagan Prize for Science Popularization

Carl Sagan Medal for Excellence in Public Communication in Planetary Science, presented by the American Astronomical Society's Division for Planetary Sciences (AAS/DPS)

Carl Sagan Center for the Study of Life in the Universe, SETI Institute

Carl Sagan's Life and Legacy as Scientist, Teacher, and Skeptic, Committee for Skeptical Inquiry

Cosmos — Full Episodes and Clips streaming online for free — Hulu, Cosmos online for free

A Tribute to Carl Sagan: Our Place in the Universe, The Skeptics Society

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