Heliocentric Theory Scientific Revolution Essay

"Heliocentric" redirects here. For the albums, see Heliocentric (Paul Weller album) and Heliocentric (The Ocean Collective album). For heliocentric orbit, see Heliocentric orbit.

Heliocentrism[1] is the astronomical model in which the Earth and planets revolve around the Sun at the center of the Solar System. Historically, Heliocentrism was opposed to geocentrism, which placed the Earth at the center. The notion that the Earth revolves around the Sun had been proposed as early as the 3rd century BC by Aristarchus of Samos,[2] but at least in the medieval world, Aristarchus's Heliocentrism attracted little attention—possibly because of the loss of scientific works of the Hellenistic Era.[3]

It was not until the 16th century that a geometric mathematical model of a heliocentric system was presented, by the Renaissance mathematician, astronomer, and Catholic cleric Nicolaus Copernicus, leading to the Copernican Revolution. In the following century, Johannes Kepler elaborated upon and expanded this model to include elliptical orbits, and Galileo Galilei presented supporting observations made using a telescope.

With the observations of William Herschel, Friedrich Bessel, and other astronomers, it was realized that the sun, while near the Barycenter of the solar system, was not at any center of the universe.

Ancient and medieval astronomy[edit]

While the sphericity of the Earth was widely recognized in Greco-Roman astronomy from at least the 3rd century BC, the Earth's daily rotation and yearly orbit around the Sun was never universally accepted until the Copernican Revolution.

While a moving Earth was proposed at least from the 4th century BC in Pythagoreanism, and a fully developed heliocentric model was developed by Aristarchus of Samos in the 3rd century BC, these ideas were not successful in replacing the view of a static spherical Earth, and from the 2nd century AD the predominant model, which would be inherited by medieval astronomy, was the geocentric model described in Ptolemy's Almagest.

The Ptolemaic system was a sophisticated astronomical system that managed to calculate the positions for the planets to a fair degree of accuracy.[4] Ptolemy himself, in his Almagest, points out that any model for describing the motions of the planets is merely a mathematical device, and since there is no actual way to know which is true, the simplest model that gets the right numbers should be used.[5] However, he rejected the idea of a spinning earth as absurd as he believed it would create huge winds. His planetary hypotheses were sufficiently real that the distances of moon, sun, planets and stars could be determined by treating orbits' celestial spheres as contiguous realities. This made the stars' distance less than 20 Astronomical Units,[6] a regression, since Aristarchus of Samos's heliocentric scheme had centuries earlier necessarily placed the stars at least two orders of magnitude more distant.

Problems with Ptolemy's system were well recognized in medieval astronomy, and an increasing effort to criticize and improve it in the late medieval period eventually led to the Copernican heliocentrism developed in Renaissance astronomy.

Classical Antiquity[edit]

See also: Greek astronomy


The non-geocentric model of the Universe was proposed by the Pythagorean philosopher Philolaus (d. 390 BC), who taught that at the center of the Universe was a "central fire", around which the Earth, Sun, Moon and Planets revolved in uniform circular motion. This system postulated the existence of a counter-earth collinear with the Earth and central fire, with the same period of revolution around the central fire as the Earth. The Sun revolved around the central fire once a year, and the stars were stationary. The Earth maintained the same hidden face towards the central fire, rendering both it and the "counter-earth" invisible from Earth. The Pythagorean concept of uniform circular motion remained unchallenged for approximately the next 2000 years, and it was to the Pythagoreans that Copernicus referred to show that the notion of a moving Earth was neither new nor revolutionary.[7]Kepler gave an alternative explanation of the Pythagoreans' "central fire" as the Sun, "as most sects purposely hid[e] their teachings".[8]

Heraclides of Pontus (4th century BC) said that the rotation of the Earth explained the apparent daily motion of the celestial sphere. It used to be thought that he believed Mercury and Venus to revolve around the Sun, which in turn (along with the other planets) revolves around the Earth.[9]Macrobius Ambrosius Theodosius (AD 395–423) 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.[10][11]

Aristarchus of Samos[edit]

The first person known to have proposed a heliocentric system, however, was Aristarchus of Samos (c. 270 BC). Like Eratosthenes, Aristarchus calculated the size of the Earth, and measured the size and distance of the Moon and Sun, in a treatise which has survived. From his estimates, he concluded that the Sun was six to seven times wider than the Earth and thus hundreds of times more voluminous. His writings on the heliocentric system are lost, but some information is known from surviving descriptions and critical commentary by his contemporaries, such as Archimedes. Some have suggested that his calculation of the relative size of the Earth and Sun led Aristarchus to conclude that it made more sense for the Earth to be moving than for the huge Sun to be moving around it. Though the original text has been lost, a reference in Archimedes' book The Sand Reckoner describes another work by Aristarchus in which he advanced an alternative hypothesis of the heliocentric model. Archimedes wrote:

You King Gelon are aware the 'universe' is the name given by most astronomers to the sphere the center of which is the center of the Earth, while its radius is equal to the straight line between the center of the Sun and the center of the Earth. This is the common account as you have heard from astronomers. But Aristarchus has brought out a book consisting of certain hypotheses, wherein it appears, as a consequence of the assumptions made, that the universe is many times greater than the 'universe' just mentioned. His hypotheses are that the fixed stars and the Sun remain unmoved, that the Earth revolves about the Sun on the circumference of a circle, the Sun lying in the middle of the orbit, and that the sphere of fixed stars, situated about the same center as the Sun, is so great that the circle in which he supposes the Earth to revolve bears such a proportion to the distance of the fixed stars as the center of the sphere bears to its surface.[12]

Aristarchus believed the stars to be very far away, and saw this as the reason why there was no visible parallax, that is, an observed movement of the stars relative to each other as the Earth moved around the Sun. The stars are in fact much farther away than the distance that was generally assumed in ancient times, which is why stellar parallax is only detectable with telescopes.

Archimedes says that Aristarchus made the stars' distance larger, suggesting that he was answering the natural objection that Heliocentrism requires stellar parallactic oscillations. He apparently agreed to the point but placed the stars so distant as to make the parallactic motion invisibly minuscule. Thus Heliocentrism opened the way for realization that the universe was larger than the geocentrists taught.[13]

Heliocentrism had been in conflict with religion before Copernicus: One of the few pieces of information we have about the reception of Aristarchus's heliocentric system comes from a passage in Plutarch's dialogue, Concerning the Face which Appears in the Orb of the Moon. According to one of Plutarch's characters in the dialogue, the philosopher Cleanthes had held that Aristarchus should be charged with impiety for "moving the hearth of the world".[14]

Seleucus of Seleucia[edit]

Since Plutarch mentions the "followers of Aristarchus" in passing, it is likely that there were other astronomers in the Classical period who also espoused Heliocentrism, but whose work was lost. The only other astronomer from antiquity known by name who is known to have supported Aristarchus' heliocentric model was Seleucus of Seleucia (b. 190 BC), a Hellenistic astronomer who flourished a century after Aristarchus in the Seleucid empire.[15] Seleucus adopted the heliocentric system of Aristarchus and is said to have proved the heliocentric theory.[16] According to Bartel Leendert van der Waerden, Seleucus may have proved the heliocentric theory by determining the constants of a geometric model for the heliocentric theory and by developing methods to compute planetary positions using this model. He may have used early trigonometric methods that were available in his time, as he was a contemporary of Hipparchus.[17] A fragment of a work by Seleucus has survived in Arabic translation, which was referred to by Rhazes (b. 865).[18]

Alternatively, his explanation may have involved the phenomenon of tides,[19] which he supposedly theorized to be caused by the attraction to the Moon and by the revolution of the Earth around the Earth-Moon 'center of mass'.

Late Antiquity[edit]

There were occasional speculations about heliocentrism in Europe before Copernicus. In Roman Carthage, the paganMartianus Capella (5th century A.D.) expressed the opinion that the planets Venus and Mercury did not go about the Earth but instead circled the Sun.[20] Capella's model was discussed in the Early Middle Ages by various anonymous 9th-century commentators[21] and Copernicus mentions him as an influence on his own work.[22]

The Ptolemaic system was also received in Indian astronomy. Aryabhata (476–550), in his magnum opus Aryabhatiya (499), propounded a planetary model in which the Earth was taken to be spinning on its axis and the periods of the planets were given with respect to the Sun. He accurately calculated many astronomical constants, such as the periods of the planets, times of the solar and lunareclipses, and the instantaneous motion of the Moon.[23][page needed][24][page needed] Early followers of Aryabhata's model included Varahamihira, Brahmagupta, and Bhaskara II.

Medieval Islamic world[edit]

See also: Astronomy in medieval Islam and Islamic cosmology

Muslim astronomers often, but not entirely accepted the Ptolemaic system and the geocentric model.[25]

Beginning in the 11th century, a tradition criticizing Ptolemy developed within Islamic astronomy, beginning with Ibn al-Haytham of Basra's Al-Shukūk 'alā Baṭalamiyūs ("Doubts Concerning Ptolemy").[26] Several Muslim scholars questioned the Earth's apparent immobility[27][28] and centrality within the universe.[29]

Abu Sa'id al-Sijzi (d. c. 1020) accepted that the Earth rotates around its axis.[30][31]

According to Al-Biruni, Sijzi invented an astrolabe called al-zūraqī based on a belief held by some of his contemporaries "That the motion we see is due to the Earth's movement and not to that of the sky."[31][32] The prevalence of this view is further confirmed by a reference from the 13th century which states:

According to the Geometers [or engineers] (muhandisīn), the earth is in constant circular motion, and what appears to be the motion of the heavens is actually due to the motion of the earth and not the stars.[31]

Early in the 11th century Alhazen wrote a scathing critique of Ptolemy's model in his Doubts on Ptolemy (c. 1028), which some have interpreted to imply he was criticizing Ptolemy's geocentrism,[33] but most agree that he was actually criticizing the details of Ptolemy's model rather than his geocentrism.[34]Abu Rayhan Biruni (b. 973) discussed the possibility of whether the Earth rotated about its own axis and around the Sun, but in his Masudic Canon, he set forth the principles that the Earth is at the center of the universe and that it has no motion of its own.[35] He was aware that if the Earth rotated on its axis, this would be consistent with his astronomical parameters,[36] but he considered it a problem of natural philosophy rather than mathematics.[31][37]

In the 12th century, some Islamic astronomers developed complete alternatives to the Ptolemaic system (although not heliocentric), such as Nur ad-Din al-Bitruji, who considered the Ptolemaic model as mathematical, and not physical.[38][39] Al-Bitruji's alternative system spread through most of Europe in the 13th century, with debates and refutations of his ideas continued up to the 16th century.[39]

Later medieval period[edit]

The Maragha school of astronomy in Ilkhanid-era Persia further developed "non-Ptolemaic" planetary models involving Earth's rotation. Notable astronomers of this school are Al-Urdi (d. 1266) Al-Katibi (d. 1277),[40] and Al-Tusi (d. 1274).

The arguments and evidence used resemble those used by Copernicus to support the Earth's motion.[27][28] The criticism of Ptolemy as developed by Averroes and by the Maragha school explicitly address the Earth's rotation but it did not arrive at explicit heliocentrism.[41] The observations of the Maragha school were further improved at the Timurid-era Samarkand observatory under Qushji (1403–1474).

European scholarship in the later medieval period actively received astronomical models developed in the Islamic world and by the 13th century was well aware of the problems of the Ptolemaic model. In the 14th century, bishop Nicole Oresme discussed the possibility that the Earth rotated on its axis, while Cardinal Nicholas of Cusa in his Learned Ignorance asked whether there was any reason to assert that the Sun (or any other point) was the center of the universe. In parallel to a mystical definition of God, Cusa wrote that "Thus the fabric of the world (machina mundi) will quasi have its center everywhere and circumference nowhere."[42]

In India, Nilakantha Somayaji (1444–1544), in his Aryabhatiyabhasya, a commentary on Aryabhata's Aryabhatiya, developed a computational system for a partially heliocentric planetary model, in which the planets orbit the Sun, which in turn orbits the Earth, similar to the Tychonic system later proposed by Tycho Brahe in the late 16th century. In the Tantrasangraha (1500), he further revised his planetary system, which was mathematically more accurate at predicting the heliocentric orbits of the interior planets than both the Tychonic and Copernican models,[23][43] but did not propose any specific models of the universe.[44] Nilakantha's planetary system also incorporated the Earth's rotation on its axis.[45] Most astronomers of the Kerala school of astronomy and mathematics seem to have accepted his planetary model.[46][47]

Renaissance-era astronomy[edit]

European astronomy before Copernicus[edit]

Some historians maintain that the thought of the Maragheh observatory, in particular the mathematical devices known as the Urdi lemma and the Tusi couple, influenced Renaissance-era European astronomy, and thus was indirectly received by Renaissance-era European astronomy and thus by Copernicus.[37][48][49][50][51] Copernicus used such devices in the same planetary models as found in Arabic sources.[52] Furthermore, the exact replacement of the equant by two epicycles used by Copernicus in the Commentariolus was found in an earlier work by Ibn al-Shatir (d. c. 1375) of Damascus.[53] Ibn al-Shatir's lunar and Mercury models are also identical to those of Copernicus.[54]

The state of knowledge on planetary theory received by Copernicus is summarized in Georg von Peuerbach's Theoricae Novae Planetarum (printed in 1472 by Regiomontanus). By 1470, the accuracy of observations by the Vienna school of astronomy, of which Peuerbach and Regiomontanus were members, was high enough to make the eventual development of heliocentrism inevitable, and indeed it is possible that Regiomontanus did arrive at an explicit theory of heliocentrism before his death in 1476, some 30 years before Copernicus.[55] While the influence of the criticism of Ptolemy by Averroes on Renaissance thought is clear and explicit, the claim of direct influence of the Maragha school, postulated by Otto E. Neugebauer in 1957, remains an open question.[41][56][57] Copernicus explicitly references several astronomers of the "Islamic Golden Age" (10th to 12th centuries) in De Revolutionibus: Albategnius (Al-Battani), Averroes (Ibn Rushd), Thebit (Thabit Ibn Qurra), Arzachel (Al-Zarqali), and Alpetragius (Al-Bitruji), but he does not show awareness of the existence of any of the later astronomers of the Maragha school.[58]

It has been argued that Copernicus could have independently discovered the Tusi couple or took the idea from Proclus's Commentary on the First Book of Euclid,[59] which Copernicus cited.[60] Another possible source for Copernicus's knowledge of this mathematical device is the Questiones de Spera of Nicole Oresme, who described how a reciprocating linear motion of a celestial body could be produced by a combination of circular motions similar to those proposed by al-Tusi.[61]

Copernican heliocentrism[edit]

Main article: Copernican heliocentrism

Nicolaus Copernicus in his De revolutionibus orbium coelestium ("On the revolution of heavenly spheres", first printed in 1543 in Nuremberg), presented a discussion of a heliocentric model of the universe in much the same way as Ptolemy in the 2nd century had presented his geocentric model in his Almagest. Copernicus discussed the philosophical implications of his proposed system, elaborated it in geometrical detail, used selected astronomical observations to derive the parameters of his model, and wrote astronomical tables which enabled one to compute the past and future positions of the stars and planets. In doing so, Copernicus moved Heliocentrism from philosophical speculation to predictive geometrical astronomy. In reality, Copernicus's system did not predict the planets' positions any better than the Ptolemaic system.[63] This theory resolved the issue of planetary retrograde motion by arguing that such motion was only perceived and apparent, rather than real: it was a parallax effect, as an object that one is passing seems to move backwards against the horizon. This issue was also resolved in the geocentric Tychonic system; the latter, however, while eliminating the major epicycles, retained as a physical reality the irregular back-and-forth motion of the planets, which Kepler characterized as a "pretzel".[64]

Copernicus cited Aristarchus in an early (unpublished) manuscript of De Revolutionibus (which still survives), stating: "Philolaus believed in the mobility of the earth, and some even say that Aristarchus of Samos was of that opinion."[65] However, in the published version he restricts himself to noting that in works by Cicero he had found an account of the theories of Hicetas and that Plutarch had provided him with an account of the Pythagoreans, Heraclides Ponticus, Philolaus, and Ecphantus. These authors had proposed a moving earth, which did not, however, revolve around a central sun.

Reception in Early Modern Europe[edit]

Main article: Copernican Revolution


The first information about the heliocentric views of Nicolaus Copernicus was circulated in manuscript completed some time before May 1, 1514.[66] Although only in manuscript, Copernicus' ideas were well known among astronomers and others. His ideas contradicted the then-prevailing understanding of the Bible. In the King James Bible (first published in 1611), First Chronicles 16:30 states that "the world also shall be stable, that it be not moved." Psalm 104:5 says, "[the Lord] Who laid the foundations of the earth, that it should not be removed for ever." Ecclesiastes 1:5 states that "The sun also ariseth, and the sun goeth down, and hasteth to his place where he arose."

Nonetheless, in 1533, Johann Albrecht Widmannstetter delivered in Rome a series of lectures outlining Copernicus' theory. The lectures were heard with interest by Pope Clement VII and several Catholic cardinals.[67] On November 1, 1536, Archbishop of CapuaNikolaus von Schönberg wrote a letter to Copernicus from Rome encouraging him to publish a full version of his theory.

However, in 1539, Martin Luther said:

"There is talk of a new astrologer who wants to prove that the earth moves and goes around instead of the sky, the sun, the moon, just as if somebody were moving in a carriage or ship might hold that he was sitting still and at rest while the earth and the trees walked and moved. But that is how things are nowadays: when a man wishes to be clever he must . . . invent something special, and the way he does it must needs be the best! The fool wants to turn the whole art of astronomy upside-down. However, as Holy Scripture tells us, so did Joshua bid the sun to stand still and not the earth."[68]

This was reported in the context of a conversation at the dinner table and not a formal statement of faith. Melanchthon, however, opposed the doctrine over a period of years.[69][70]

Publication of de Revolutionibus (1543)[edit]

Nicolaus Copernicus published the definitive statement of his system in De Revolutionibus in 1543. Copernicus began to write it in 1506 and finished it in 1530, but did not publish it until the year of his death. Although he was in good standing with the Church and had dedicated the book to Pope Paul III, the published form contained an unsigned preface by Osiander defending the system and arguing that it was useful for computation even if its hypotheses were not necessarily true. Possibly because of that preface, the work of Copernicus inspired very little debate on whether it might be heretical during the next 60 years. There was an early suggestion among Dominicans that the teaching of Heliocentrism should be banned, but nothing came of it at the time.

Some years after the publication of De RevolutionibusJohn Calvin preached a sermon in which he denounced those who "pervert the order of nature" by saying that "the sun does not move and that it is the earth that revolves and that it turns".[71]

On the other hand, Calvin is not responsible for another famous quotation which has often been misattributed to him: "Who will venture to place the authority of Copernicus above that of the Holy Spirit?" It has long been established that this line cannot be found in any of Calvin's works.[72][73][74] It has been suggested[75] that the quotation was originally sourced from the works of Lutheran theologian Abraham Calovius.

Tycho Brahe's geo-heliocentric system c. 1587[edit]

Main article: Tychonic system

Prior to the publication of De Revolutionibus, the most widely accepted system had been proposed by Ptolemy, in which the Earth was the center of the universe and all celestial bodies orbited it. Tycho Brahe, arguably the most accomplished astronomer of his time, advocated against Copernicus's heliocentric system and for an alternative to the Ptolemaic geocentric system: a geo-heliocentric system now known as the Tychonic system in which the five then known planets orbit the sun, while the sun and the moon orbit the earth.

Tycho appreciated the Copernican system, but objected to the idea of a moving Earth on the basis of physics, astronomy, and religion. The Aristotelian physics of the time (modern Newtonian physics was still a century away) offered no physical explanation for the motion of a massive body like Earth, whereas it could easily explain the motion of heavenly bodies by postulating that they were made of a different sort substance called aether that moved naturally. So Tycho said that the Copernican system "... expertly and completely circumvents all that is superfluous or discordant in the system of Ptolemy. On no point does it offend the principle of mathematics. Yet it ascribes to the Earth, that hulking, lazy body, unfit for motion, a motion as quick as that of the aethereal torches, and a triple motion at that."[76] Likewise, Tycho took issue with the vast distances to the stars that Aristarchus and Copernicus had assumed in order to explain the lack of any visible parallax. Tycho had measured the apparent sizes of stars (now known to be illusory – see stellar magnitude), and used geometry to calculate that in order to both have those apparent sizes and be as far away as Heliocentrism required, stars would have to be huge (much larger than the sun; the size of Earth's orbit or larger). Regarding this Tycho wrote, "Deduce these things geometrically if you like, and you will see how many absurdities (not to mention others) accompany this assumption [of the motion of the earth] by inference."[77] He also cited the Copernican system's "opposition to the authority of Sacred Scripture in more than one place" as a reason why one might wish to reject it, and observed that his own geoheliocentric alternative "offended neither the principles of physics nor Holy Scripture".[78]

The Jesuit astronomers in Rome were at first unreceptive to Tycho's system; the most prominent, Clavius, commented that Tycho was "confusing all of astronomy, because he wants to have Mars lower than the Sun."[79] However, after the advent of the telescope showed problems with some geocentric models (by demonstrating that Venus circles the sun, for example), the Tychonic system and variations on that system became very popular among geocentrists, and the Jesuit astronomer Giovanni Battista Riccioli would continue Tycho's use of physics, stellar astronomy (now with a telescope), and religion to argue against Heliocentrism and for Tycho's system well into the seventeenth century (see Riccioli).

Galileo Galilei[edit]

Publication of Letters on Sunspots (1613)[edit]

Galileo was able to look at the night sky with the newly invented telescope. Then he published his discoveries in Letters on Sunspots that the Sun rotated and that Venus exhibited a full range of phases. These discoveries were not consistent with the Ptolemeic model of the solar system. As the Jesuit astronomers confirmed Galileo's observations, the Jesuits moved toward Tycho's teachings.[80]

Publication of Letter to the Grand Duchess (1615)[edit]

In a Letter to the Grand Duchess Christina, Galileo defended Heliocentrism, and claimed it was not contrary to Scriptures (see Galileo affair). He took Augustine's position on Scripture: not to take every passage literally when the scripture in question is in a Bible book of poetry and songs, not a book of instructions or history. The writers of the Scripture wrote from the perspective of the terrestrial world, and from that vantage point the sun does rise and set. In fact, it is the Earth's rotation which gives the impression of the sun in motion across the sky.

1616 ban against Copernicanism[edit]

Main article: Galileo affair

In February 1615, prominent Dominicans including Thomaso Caccini and Niccolò Lorini brought Galileo's writings on Heliocentrism to the attention of the Inquisition, because they appeared to violate Holy Scripture and the decrees of the Council of Trent.[81][82] Cardinal and Inquisitor Robert Bellarmine was called upon to adjudicate, and wrote in April that treating Heliocentrism as a real phenomenon would be "a very dangerous thing," irritating philosophers and theologians, and harming "the Holy Faith by rendering Holy Scripture as false."[83]

In January 1616 Msgr. Francesco Ingoli addressed an essay to Galileo disputing the Copernican system. Galileo later stated that he believed this essay to have been instrumental in the ban against Copernicanism that followed in February.[84] According to Maurice Finocchiaro, Ingoli had probably been commissioned by the Inquisition to write an expert opinion on the controversy, and the essay provided the "chief direct basis" for the ban.[85] The essay focused on eighteen physical and mathematical arguments against Heliocentrism. It borrowed primarily from the arguments of Tycho Brahe, and it notedly mentioned the problem that Heliocentrism requires the stars to be much larger than the sun. Ingoli wrote that the great distance to the stars in the heliocentric theory "clearly proves ... the fixed stars to be of such size, as they may surpass or equal the size of the orbit circle of the Earth itself."[86] Ingoli included four theological arguments in the essay, but suggested to Galileo that he focus on the physical and mathematical arguments. Galileo did not write a response to Ingoli until 1624.[87]

In February 1616, the Inquisition assembled a committee of theologians, known as qualifiers, who delivered their unanimous report condemning Heliocentrism as "foolish and absurd in philosophy, and formally heretical since it explicitly contradicts in many places the sense of Holy Scripture." The Inquisition also determined that the Earth's motion "receives the same judgement in philosophy and ... in regard to theological truth it is at least erroneous in faith."[88] Bellarmine personally ordered Galileo

"to abstain completely from teaching or defending this doctrine and opinion or from discussing it... to abandon completely... the opinion that the sun stands still at the center of the world and the earth moves, and henceforth not to hold, teach, or defend it in any way whatever, either orally or in writing."

— Bellarmine and the Inquisition's injunction against Galileo, 1616[89]

In March, after the Inquisition's injunction against Galileo, the papal Master of the Sacred Palace, Congregation of the Index, and Pope banned all books and letters advocating the Copernican system, which they called "the false Pythagorean doctrine, altogether contrary to Holy Scripture."[89][90] In 1618 the Holy Office recommended that a modified version of Copernicus' De Revolutionibus be allowed for use in calendric calculations, though the original publication remained forbidden until 1758.[90]

Publication of Epitome astronomia Copernicanae (1617–1621)[edit]

In Astronomia nova (1609), Johannes Kepler had used an elliptical orbit to explain the motion of Mars. In Epitome astronomiae Copernicanae he developed a heliocentric model of the solar system in which all the planets have elliptical orbits. This provided significantly increased accuracy in predicting the position of the planets. Kepler's ideas were not immediately accepted. Galileo for example completely ignored Kepler's work. Kepler proposed Heliocentrism as a physical description of the solar system and Epitome astronomia Copernicanae was placed on the index of prohibited books despite Kepler being a Protestant.

Publication of Dialogue concerning the two chief world systems[edit]

Pope Urban VIII encouraged Galileo to publish the pros and cons of Heliocentrism. Galileo's response, Dialogue concerning the two chief world systems (1632), clearly advocated Heliocentrism, despite his declaration in the preface that,

I will endeavour to show that all experiments that can be made upon the Earth are insufficient means to conclude for its mobility but are indifferently applicable to the Earth, movable or immovable...[91]

and his straightforward statement,

I might very rationally put it in dispute, whether there be any such centre in nature, or no; being that neither you nor any one else hath ever proved, whether the World be finite and figurate, or else infinite and interminate; yet nevertheless granting you, for the present, that it is finite, and of a terminate Spherical Figure, and that thereupon it hath its centre...[91]

Some ecclesiastics also interpreted the book as characterizing the Pope as a simpleton, since his viewpoint in the dialogue was advocated by the character Simplicio. Urban VIII became hostile to Galileo and he was again summoned to Rome.[92] Galileo's trial in 1633 involved making fine distinctions between "teaching" and "holding and defending as true". For advancing heliocentric theory Galileo was forced to recant Copernicanism and was put under house arrest for the last few years of his life.

According to J. L. Heilbron,[93] informed contemporaries of Galileo's:

"appreciated that the reference to heresy in connection with Galileo or Copernicus had no general or theological significance."

Age of Reason[edit]

Further information: Age of Reason, 17th-century philosophy, and Scientific revolution

René Descartes postponed, and ultimately never finished, his treatise The World, which included a heliocentric model,[94] but the Galileo affair did little to slow the spread of Heliocentrism across Europe, as Kepler's Epitome of Copernican Astronomy became increasingly influential in the coming decades.[95] By 1686 the model was well enough established that the general public was reading about it in Conversations on the Plurality of Worlds, published in France by Bernard le Bovier de Fontenelle and translated into English and other languages in the coming years. It has been called "one of the first great popularizations of science."[94]

In 1687, Isaac Newton published Philosophiæ Naturalis Principia Mathematica, which provided an explanation for Kepler's laws in terms of universal gravitation and what came to be known as Newton's laws of motion. This placed Heliocentrism on a firm theoretical foundation, although Newton's Heliocentrism was of a somewhat modern kind. Already in the mid-1680s he recognized the "deviation of the Sun" from the centre of gravity of the solar system.[96] For Newton it was not precisely the centre of the Sun or any other body that could be considered at rest, but "the common centre of gravity of the Earth, the Sun and all the Planets is to be esteem'd the Centre of the World", and this centre of gravity "either is at rest or moves uniformly forward in a right line". Newton adopted the "at rest" alternative in view of common consent that the centre, wherever it was, was at rest.[97]

Meanwhile, the Church remained opposed to Heliocentrism as a literal description, but this did not by any means imply opposition to all astronomy; indeed, it needed observational data to maintain its calendar. In support of this effort it allowed the cathedrals themselves to be used as solar observatories called meridiane; i.e., they were turned into "reverse sundials", or gigantic pinhole cameras, where the Sun's image was projected from a hole in a window in the cathedral's lantern onto a meridian line.

In 1664, Pope Alexander VII published his Index Librorum Prohibitorum Alexandri VII Pontificis Maximi jussu editus (Index of Prohibited Books, published by order of Alexander VII, P.M.) which included all previous condemnations of heliocentric books.[98]

In the mid-eighteenth century the Church's opposition began to fade. An annotated copy of Newton's Principia was published in 1742 by Fathers le Seur and Jacquier of the Franciscan Minims, two Catholic mathematicians, with a preface stating that the author's work assumed Heliocentrism and could not be explained without the theory. In 1758 the Catholic Church dropped the general prohibition of books advocating Heliocentrism from the Index of Forbidden Books.[99] The Observatory of the Roman College was established by Pope Clement XIV in 1774 (nationalized in 1878, but re-founded by Pope Leo XIII as the Vatican Observatory in 1891). In spite of dropping its active resistance to Heliocentrism, the Catholic Church did not lift the prohibition of uncensored versions of Copernicus's De Revolutionibus or Galileo's Dialogue. The affair was revived in 1820, when the Master of the Sacred Palace (the Church's chief censor), Filippo Anfossi, refused to license a book by a Catholic canon, Giuseppe Settele, because it openly treated heliocentrism as a physical fact.[100] Settele appealed to pope Pius VII. After the matter had been reconsidered by the Congregation of the Index and the Holy Office, Anfossi's decision was overturned.[100] Pius VII approved a decree in 1822 by the Sacred Congregation of the Inquisition to allow the printing of heliocentric books in Rome. Copernicus's De Revolutionibus and Galileo's Dialogue were then subsequently omitted from the next edition of the Index when it appeared in 1835.

Reception in Judaism[edit]

Already in the Talmud, Greek philosophy and science under general name "Greek wisdom" were considered dangerous. They were put under ban then and later for some periods.

The first Jewish scholar to describe the Copernican system, albeit without mentioning Copernicus by name, was Maharal of Prague, his book "Be'er ha-Golah" (1593). Maharal makes an argument of radical skepticism, arguing that no scientific theory can be reliable, which he illustrates by the new-fangled theory of heliocentrism upsetting even the most fundamental views on the cosmos.[101]

Copernicus is mentioned in the books of David Gans (1541–1613), who worked with Tycho Brahe and Johannes Kepler. Gans wrote two books on astronomy in Hebrew: a short one "Magen David" (1612) and a full one "Nehmad veNaim" (published only in 1743). He described objectively three systems: Ptolemy, Copernicus and of Tycho Brahe without taking sides. Joseph Solomon Delmedigo (1591–1655) in his "Elim" (1629) says that the arguments of Copernicus are so strong, that only an imbecile will not accept them.[102] Delmedigo studied at Padua and was acquainted with Galileo.[103]

An actual controversy on the Copernican model within Judaism arises only in the early 18th century. Most authors in this period accept Copernican heliocentrism, with opposition from David Nieto and Tobias Cohn. Both of these authors argued against heliocentrism on grounds of contradictions to scripture. Nieto merely rejected the new system on those grounds without much passion, whereas Cohn went so far as to call Copernicus "a first-born of Satan", though he also acknowledged[104] that he would have found it difficult to counter one particular objection based on a passage from the Talmud.

In the 19th century two students of the Hatam sofer wrote books that were given approbations by him even though one supported heliocentrism and the other geocentrism. The one, a commentary on Genesis Yafe’ah le-Ketz[105] written by R. Israel David Schlesinger resisted a heliocentric model and supported geocentrism.[106] The other, Mei Menuchot[107] written by R. Eliezer Lipmann Neusatz encouraged acceptance of the heliocentric model and other modern scientific thinking.[108]

Since the 20th century most Jews have not questioned the science of heliocentrism. Exceptions include Shlomo Benizri[109] and R. M.M. Schneerson of Chabad who argued that the question of heliocentrism vs. geocentrism is obsolete because of the relativity of motion.[110] Schneerson's followers in Chabad continue to deny the heliocentric model.[111]

The view of modern science[edit]

Kepler's laws of planetary motion were used as arguments[citation needed] in favor of the heliocentric hypothesis. Three apparent proofs of the heliocentric hypothesis were provided in 1727 by James Bradley, in 1838 by Friedrich Wilhelm Bessel and in 1851 by Foucault. Bradley discovered the stellar aberration, proving the relative motion of the earth. Bessel proved that the parallax of a star was greater than zero by measuring the parallax of 0.314 arcseconds of a star named 61 Cygni. In the same year Friedrich Georg Wilhelm Struve and Thomas Henderson measured the parallaxes of other stars, Vega and Alpha Centauri.

The thinking that the heliocentric view was also not true in a strict sense was achieved in steps. That the Sun was not the center of the universe, but one of innumerable stars, was strongly advocated by the mystic Giordano Bruno. Over the course of the 18th and 19th centuries, the status of the Sun as merely one star among many became increasingly obvious. By the 20th century, even before the discovery that there are many galaxies, it was no longer an issue.

The concept of an absolute velocity, including being "at rest" as a particular case, is ruled out by the principle of relativity, also eliminating any obvious "center" of the universe as a natural origin of coordinates. Some forms of Mach's principle consider the frame at rest with respect to the distant masses in the universe to have special properties.

Even if the discussion is limited to the solar system, the Sun is not at the geometric center of any planet's orbit, but rather approximately at one focus of the elliptical orbit. Furthermore, to the extent that a planet's mass cannot be neglected in comparison to the Sun's mass, the center of gravity of the solar system is displaced slightly away from the center of the Sun.[97] (The masses of the planets, mostly Jupiter, amount to 0.14% of that of the Sun.) Therefore, a hypothetical astronomer on an extrasolar planet would observe a small "wobble" in the Sun's motion.

Modern use of geocentric and heliocentric[edit]

In modern calculations the terms "geocentric" and "heliocentric" are often used to refer to reference frames. In such systems the origin in the center of mass of the Earth, of the Earth–Moon system, of the Sun, of the Sun plus the major planets, or of the entire solar system can be selected; see center-of-mass frame. Right Ascension and Declination are examples of geocentric coordinates, used in Earth-based observations, while the heliocentric latitude and longitude are used for orbital calculations. This leads to such terms as "heliocentric velocity" and "heliocentric angular momentum". In this heliocentric picture, any planet of the Solar System can be used as a source of mechanical energy because it moves relatively to the Sun. A smaller body (either artificial or natural) may gain heliocentric velocity due to gravity assist – this effect can change the body's mechanical energy in heliocentric reference frame (although it will not changed in the planetary one). However, such selection of "geocentric" or "heliocentric" frames is merely a matter of computation. It does not have philosophical implications and does not constitute a distinct physical or scientific model. From the point of view of General Relativity, inertial reference frames do not exist at all, and any practical reference frame is only an approximation to the actual space-time, which can have higher or lower precision.

See also[edit]


  1. ^optinonally capitalised, Heliocentrism or heliocentrism, according to The Shorter Oxford English Dictionary (6th ed., 2007). The term is a learned formation based on Greekἥλιοςhelios "sun" and κέντρονkentron "center"; the adjective heliocentric is first recorded in English (as heliocentrick) in 1685, after New Latinheliocentricus, in use from about the same time (Johann Jakob Zimmermann, Prodromus biceps cono ellipticæ et a priori demonstratæ planetarum theorices, 1679, p. 28). The abstract noun in -ism is more recent, recorded from the late 19th century (e.g. in Constance Naden, Induction and Deduction: A Historical and Critical Sketch of Successive Philosophical Conceptions Respecting the Relations Between Inductive and Deductive Thought and Other Essays (1890), p. 76: "Copernicus started from the observed motions of the planets, on which astronomers were agreed, and worked them out on the new hypothesis of Heliocentrism"), modelled after German Heliocentrismus or Heliozentrismus (c. 1870).
  2. ^Dreyer (1953), pp.135–48; Linton (2004), pp.38–9). The work of Aristarchus's in which he proposed his heliocentric system has not survived. We only know of it now from a brief passage in Archimedes's The Sand Reckoner.
  3. ^according to Lucio Russo, the heliocentric view was expounded in Hipparchus's work on gravity. (source: Lucio Rosso, The Forgotten Revolution, How Science was Born in 300BC and Why it had to be Reborn, pp 293-296)
  4. ^
Andreas Cellarius's illustration of the Copernican system, from the Harmonia Macrocosmica (1708).
A hypothetical geocentric model of the solar system (upper panel) in comparison to the heliocentric model (lower panel).
Aristarchus's 3rd century BC calculations on the relative sizes of the Earth, Sun and Moon, from a 10th-century AD Greek copy
Nicholas of Cusa, 15th century, asked whether there was any reason to assert that any point was the center of the universe.
In this depiction of the Tychonic system, the objects on blue orbits (the Moon and the Sun) revolve around the Earth. The objects on orange orbits (Mercury, Venus, Mars, Jupiter, and Saturn) revolve around the Sun. Around all is a sphere of fixed stars, located just beyond Saturn.
In the 17th century AD Galileo Galilei opposed the Roman Catholic Church by his strong support for Heliocentrism

1451 -- Christopher Columbus (d.1506) is born as is Amerigo Vespucci (d. 1512), explorers.

1462 -- One of the major publications of Renaissance natural philosophy, the Epitome of Ptolemy's Almagest appears; the authors, Georg Peurbach (1423-1461) and Johannes Regiomontanus (1436-1476), symbolize a shift from reverence for Ptolemy and antiquity to respect coupled with confident innovation.

1469 -- Publication of the highly influential Corpus Hermeticum, a collection of writings (we now know) to have been written in the early Christian era but then thought to have been written with great authority by Hermes Trismegistus (perhaps Thoth or Moses) living c.1800 BC.

1472 -- Georg Peurbach's New Theory of the Planets (1454) sought to reconcile geometric descriptive models for predicting planetary motions by employing homocentric (nested concentric) celestial spheres.

1473 -- Nicolas Copernicus (1473-1543) born.

1486 -- The Malleus Malificarum (The Hammer of the Witches) is published as an influential guidebook to identifying witches and bringing them to punishment.

1494 -- Giovanni Pico della Mirandola (1463-1494) attacks practical magic, especially, astrology, as it calls into questions traditional notions of human free will; this concern underscores longstanding issues associated with the Condemnations of 1270 and 1277 which seems to have undermined the authority of Aristotle.

1514 -- The initial appearance of the heliocentric theory of Nicholas Copernicus (1473-1543) is associated with the private circulation of a manuscript known as the Commentariolus (The Little Commentary) which was published many years later.

1518 -- The London College of Physicians is granted a royal charter and functions both as a traditional professional guild as well as a learned society.

1522 -- Ferdinand Magellan famously completes the first circumnavigation of the globe.

1530 -- Girolamo Fracastoro (1475-1553) provides one of the first descriptions of a new disease in a work entitled Syphilis, or the French Disease. As an aside, the Italians called it the French disease, the French called it Italian disease.

As in England, the French established a Collège Royal in Paris, its purpose was the advancement of learning which included lectures open to the public and a forum for practitioners in medicine, philosophy, and mathematics.

1530-1536 -- Publication of Portraits of Living Plants, by Otto Brunfels's (c.1489-1534), a botanical work that employed freshly drawn illustrations from living plants, undermining the practice of copying drawings from existing accounts.

1531 -- Juan Luis Vives (1492-1540) in his On the Disciplines argues for the reform of education and a more receptive approach to skills traditionally associated with the craft and trade traditions.

1532 -- Peter Apian (1495-1552) and Fracastoro observe that the tail of the comet his year, later known as Halley's Comet, pointed away from the sun, a detail also recognized by Regiomontanus.

1533 -- As the Hermetic tradition unfolded, Heinrich Cornelius Agrippa's (1486-1535) published his On Occult Philosophy.

1538 -- Girolamo Fracastoro continued to explore cosmological and technical alternatives to Ptolemy in his Homocentrica, again employing nested concentric spheres rather than deferents and epicycles associated with Ptolemy's Almagest.

1540 -- Georg Joachim Rheticus (1514-1574), a friend of Copernicus and the presumed author, provides an account of the heliocentric hypothesis in his Narratio prima (First Account).

1543 -- One of the most famous publications in natural philosophy was the anatomical book of Andreas Vesalius (1514-1564), De fabrica (On the Fabric of the Human Body). It was arguably the most important anatomical texts of the century, at once criticizing the work of the ancients, principally Galen, which offering new illustrations based on first-hand observation and fresh dissections.

In the same year appeared Copernicus' heliocentric theory' in his De revolutionibus orbium coelestium (On the Revolutions of the Celestial Spheres), by one tradition, these two works, if only symbolically, launched the 'Scientific Revolution'.

1545 -- In mathematics, Girolamo Cardano's (1501-1576) The Great Art contained many algebraic innovations and new methods for treating equations of the third degree.

In medicine, Ambroise Paré (1510-1590) introduced new methods in surgery and for treating wounds, arguing for ointments rather than boiling oils.

1551 -- Deriving his results from Copernicus' data and planetary models, the German astronomer Erasmus Reinhold (1511-1553) publishes his Prutenic Tables, which for many astronomers replaced the outdated efforts associated with the Alphonsine Tables (1252). Reinhold's efforts were not seriously challenged until Kepler Rudolphine Tables, which were based on Tycho's data and Kepler's new calculation methods.

Founding of the Collegio Romano, as a Jesuit university, many of whose teachers and students were active scientists during the Scientific Revolution.

1553 -- A man of religious conviction, Michael Servetus (1511-1553) proposed a radical new theory concerning the pulmonary circulation of the blood, a theory motivated in part by esoteric theological concerns involving the trinity. Servetus was found guilty of heresy and burned at the stake in Geneva by the religious reformer, John Calvin.

1554 -- Long considered a major precursor to Galileo Galilei, the Italian Giovanni Battista Benedetti (1530-1590) opposed the work of Aristotle arguing that freely falling bodies move with speeds proportional to weight.

1556 -- In his influential De re metallica (later translated by President H. Hoover), Georgius Agricola's (1494-1555) presented a detailed and sophistical text concerning mining and metallurgy; a handsome volume, it was lavishly illustrated with detailed woodcuts.

1558 -- Sprawling in scope and arguably less than critical in method, Giambattista della Porta's (1535-1615) Natural Magic was widely sited on numerous topics, from theories of vision to sympathetic attraction; della Porta was concerned to demonstrate that many marvels were natural not demonic.

1559 -- A noted Renaissance anatomist, Realdo Colombo's (1510-1559) De re anatomica (On Anatomy) treats pulmonary circulation of the blood, and like Vesalius, argues against a number of conclusions put forward by the ancient anatomist, Galen.

1561 -- Gabriele Falloppio (1523-1562) announces his discovery of the fallopian tubes in his Anatomical Observations.

1564 -- Galileo Galilei born at Pisa, Italy, February 16; Michelangelo Buonarroti dies at Florence, 18 February; William Shakespeare born in England, 23 April.

1566 -- Publication of the works of Pedro Nunez (1502-1578) on navigation, explaining the use of new instruments and how to sail on a great circle course.

1569 -- The noted cartographer Gerard Mercator (1512-1594) publishes his justly famous cartographic projection system.

1570 -- The noted geometer and some-time mystic John Dee (1527-1608) publishes an influential Preface in an English translation of Euclid's geometry.

1572 -- A famous year known for 'Tycho's Star' or the 'Star of 1572' witnessed a dramatic supernova, the talk of Europe. Tycho published De nova stella in the following year, 1573. The star blazed for 18 months as brightly as -4 magnitude. Its key importance, by tradition and as Tycho and others argued, was that the New Star was clearly located beyond the sphere of the Moon. If this were so, it would undermine the Scholastic belief, adapted from Aristotle, that the heavens were immutable.

1576 -- An early account of Copernicus's heliocentric theory, and a description of the cosmos and distribution of the stars as infinitely extended, is offered by the Englishman Thomas Digges (c.1546-1595) in the appendix to a work by his father, Leonard Digges, possibly a Copernican himself. An infinity of stars may have suggested to some the possibility of a plurality of worlds, which in turn eventually raised theological concern.

In this year construction began on the observatory made famous by Tycho Brahe's (1541-1601), Uraniborg, the 'Fortress of the Heavens, on the Danish island of Hven (now a possession of Sweden). Here Tycho made observations and collected astronomical data aided, over a period of nearly twenty years, by some 48 assistants.

1577 -- The year of the 'Comet of 1577' made famous by Tycho Brahe, and again challenging a central tenet inherited from Aristotle, that the celestial spheres were 'solid' perhaps even crystalline. Because the path of the comet seemed to many astronomers to be above the sphere of the moon (that is, superlunary) the apparent path of the comet would 'shatter' anything in its path. If Tycho's observations 'shattered the crystalline spheres' then a reasonable question might be 'What moves the planets'.

1582 -- Pope Gregory XIII suggested reform of the Julian calendar, thus leading much of Catholic Europe away from the Julian (Old Style) calendar to the Gregorian (New Style).

1584 -- A talented clockmaker, Joost Brugi (1552-1632) invents a novel design for an escapement that greatly increased accuracy.

1585 -- In mathematics, Simon Stevin (1548-1620) proposes the use of decimals.

1587 -- Conrad Gessner (1516-1565) publishes a massive and highly influential work, the History of Animals.

1588 -- Thomas Harriot (c.1560-1621) travels to what would be called America and, in his A Briefe and True Report of the New Found Land of Virginia discusses its wonders, among them tobacco. It appears Harriot may have died from this new world vice, the American disease?

Although steeped in controversy, the geo-heliocentric model of Tycho Brahe was brought to light in 1588. Here Brahe argued for a model whereby the planets are imagined to revolve around the Sun while, in turn, the Sun revolved around the fixed, central earth.

1591 -- In mathematics, Francois Viète's (1540-1603) published his Introduction to the Analytical Art, a brilliant work on analytic geometry by yet another man from Poitou.

1596 -- Gresham College, founded by the London merchant Sir Thomas Gresham, was designed to provide public lectures on a variety of subjects from astronomy and geometry to concerns in medicine. By one tradition, Gresham College was a key gathering place for the core group that founded the Royal Society of London.

In his first publication in astronomy, Johannes Kepler's Cosmographic Mystery presented a stridently Copernican worldview dedicated to drawing together mathematical astronomy, physics, and a quasi-Pythogorean religious perspective in hope of a new astronomy.

1599 -- Tycho Brahe, having been ousted from Uraniborg by the King of Denmark, moves to Benateky, outside Prague, under the patronage of Rudolph II, Emperor of the Holy Roman Empire.

1600 -- Giordano Bruno (1548-1600), an early Copernican, albeit philosophical and religious rather than technical, Bruno also argued form an infinite universe and a plurality of worlds. He was burned at the stake in Rome for his heretical opinions.

1600 -- In his On the Magnet the Englishman William Gilbert (1540-1603) provided a hyper-empirical study of magnets, magnetism, and electricity with speculations about cosmology. Gilbert collected dozen of diamonds to magnetize, rub magnets with garlic, and otherwise to the English tradition to extreme lengths. It is a pioneering classic in 'empirical' method.

1601 -- Thomas Harriot (c.1560-1521) proposed the sine law of refraction, which he failed to publish. Tycho Brahe dies at his castle new Prague.

Tycho Brahe dies 24 October in Prague and Kepler soon appointed Imperial Mathematician on 6 November; Kepler was able to retain Tycho's astronomical data following a lawsuit with Tycho's heirs.

1603 -- The Holy Roman Emperor, Rudolph II, becomes the patron of Johannes Kepler, who thus becomes Imperial Mathematician.

The Accademia dei Lincei (Academy of Lynxes or Lynx Eyed) is established in Rome, by Frederigo Cesi, as private learned society dedicated to natural philosophy.

1604 -- In optics, Johannes Kepler publishes his Ad vitellioem paralipomena quibus astronomiae pars optica traditor (The Optical Part of Astronomy) where he argues that light rays are rectilinear, that they diminish in intensity by the inverse square of their distance as they travel from the light source. Kepler also argues that the retina is the seat of vision, and it is there that a 'pictura' is formed, an inverted image that is somehow transmitted to the 'seat of judgment'.

1607 -- Galileo Galilei (1564-1642) demonstrates that a projectile follows a parabolic path.

1608 -- The telescope (sometime translated as 'spyglass') is invented in the Netherlands; it employs a convex objective lens and a concave eyepiece.

1609 -- Galileo Galilei constructs his first telescope and turns it toward the heavens; his instruments begin at magnifications of approximately 3X and 10X, the most powerful achieving a magnification of 30X, an instrument he eventually gave away as a gift.

Johannes Kepler's (1571-1630) Astronomia nova (New Astronomy) shows that Mars moves non-uniformly in an elliptical path and proposes a quasi-magnetic power or virtue emanating from the sun (a curious bi-polar magnet) as partial explanation for the planetary motions.

Thomas Harriot in England independently obtains or builds a telescope and begins to observe the heavens; Harriot eventually makes drawings of the heavenly bodies, most notably the moon.

1610 -- In his highly influential Sidereal Messenger, Galileo Galilei publishes his telescopic findings with subtle Copernican twists. Among his observations, Galileo argues there are innumerable stars invisible to the naked eye, mountains on the Moon (which he eventually measures), and four moons circling Jupiter. These observations were made for the most part in 1609; later in 1610 Galileo observes the phases of Venus, which suggested to him that waning and waxing planet must circle the Sun. Further, Galileo noted that Saturn appeared to have 'handles' (anses) and troubled over what could give rise to such an appearance; Huygens would later propose a brilliant hypothesis which served as one of the most subtle arguments for the motion of earth.

1611 -- Johannes Kepler's Dioptrics analyzes optical refraction and proposes a practical means to improve the Galilean telescope.

1612 -- Simon Marius (b. 1573) mentions for the first time (in modern Europe) the Andromeda galaxy, now known as M31. As Ismaël Boulliau later noted (1667) the galactic cloud had been observed centuries before by Abd al-Rahman al-Sufi.

1613 -- In his Letters on Sunspots Galileo took exception with the views presented by the Jesuit astronomer, Christopher Scheiner (1573-1650). Here Galileo appears clearly in the Copernican camp and also provides an early formulation for the principle of inertia.

1614 -- In mathematics, John Napier (1550-1617) in his Mirifici logarithmorum canonis descripto (Description of the Wonderful Principle of Logarithms) establishes rules for logarithms and supplies useful tables.

1616 -- The year of the infamous Injunction against Galileo, the famous Italian astronomer is warned by the Inquisition not to hold or defend the hypothesis asserted in Copernicus' On the Revolutions, though it has been debated whether he was admonished not to 'teach in any way' the heliocentric theory. This work was in turn placed on the Index of Prohibited Books until corrected.

1618 -- A famous 'controversy on comets' erupted in this year involving Galileo and prominent Jesuit astronomers.

1619 -- Johannes Kepler's Harmonice mundi (Harmonies of the World) presents his so-called 'Third Law' which draws attention to the relationship between the annual periods of the planets and their mean distances from the sun.

1620 -- The English attorney and advocate of the 'New Science', Francis Bacon (1561-1626) published his justly famous Novum organum, which sought to establish a method based on observation and experiment in opposition to Aristotle (who wrote the 'original' Organon).

1622 -- Tommaso Campanella (1568-1639) published his Apologia pro Galilaeo writing in support of Galileo's Copernicanism and providing supporting arguments, among many other things, for the relationship between science and religion.

Christian Severin (Longomontanus) (1563-1647), Tycho Brahe's former assistant, reminds astronomers of the geometrical equivalence of the Ptolemaic, Tychonic, and Copernican models; Longomontanus devises a simple variation on the Tychonic model by retaining Tycho's configuration but asserting that the central earth rotated daily, thus removing that requirement for the sphere of fixed stars.

1623 -- Galileo publishes his strategic essay, The Assayer where he argues against Aristotle and the Scholastics in favor of mathematical and experimental methods, moving deftly across many topics, from statics and dynamics to his theory of matter.

1624 -- The French philosopher Pierre Gassendi (1592-1655), opposing Scholasticism, argues for what has been called 'mitigated skepticism' whereby natural philosophy would be content with empirical methods and probable, not certain, conclusions.

1626 -- In his New Atlantis Francis Bacon present an idealized institution of learning based on collaborative research turned to the common good. Bacon would later become a symbol and rallying cry for the core group that founded the Royal Society of London. Bacon's principles of cooperation and utility were also repeated by Huygens and others as they lobbied for the establishment of the Académie des Sciences in Paris.

1627 -- Johannes Kepler's Rudolphine Tables, based on Tycho's data and his own laws of planetary motion, provide the most accurate astronomical tables up to that time.

1628 -- A classic work in the history of physiology and medicine is published by William Harvey (1578-1657), his Anatomical Exercises on the Movement of the Heart and Blood, or De motu cordis. Here Harvey employed brilliant experiments and new quantitative arguments to show that the blood circulates, thereby opposing Galen and other ancients.

1630 -- The French physician Théophraste Renaudot, originally from Loudun, establishes the Bureau d'Adresse in Paris, a clearinghouse for local public services and a new forum for learned communication. The Bureau d'Adresse offered weekly conferences and debates, which were open to the public, dealing with a variety of issues, many of them scientific, medical, and philosophical. Renaudot's sons continued the efforts of their father by making many of the topics of discussion available in print, first in French, later in English.

Christopher Scheiner, a talented Jesuit astronomer, presented detailed observations of sunspots, thereby adding his voice, at least in part, to that of Galileo in challenging Aristotelian notions and methods.

1631 -- Pierre Gassendi, familiar with Kepler's astronomical tables, becomes the first to observe a transit of the planet Mercury across the disc of the sun. His data for Mercury were used by Boulliau in his Astronomia Philolaïca (Paris 1645).

1632 -- In one of the major publications of the century, Galileo's Dialogue Concerning the Two Chief World Systems, Ptolemaic and Copernican argues for a Copernican system; Galileo uses every tactic available to him, drawing on his telescopic findings, his new view of motion, and not a little rhetorical skill.

1633 -- Galileo is called before the Inquisition in Rome; he is vehemently suspected of heresy for supporting and teaching the Copernicanism hypothesis. After he abjured, Galileo was placed under house arrest for the remainder of his life, his visitors, his mail, and his daily actions were monitored. While the Dialogue on the Two Chief World Systems was placed on the Index of Prohibited Books, Galileo lived to see it translated into Latin, for a larger European audience, and he also saw his second major work, the Discours on the Two New Science published (Leiden, 1638).

1634 -- Kepler's Somnium (The Dream) was published after his death, a fanciful account of a voyage to the Moon. The work provides subtle arguments for the Copernican hypothesis and is arguably among the first pieces of 'science fiction' writing.

1637 -- One of the classic essays of the century, Descartes' Discourse on Method was published along with his Geometry. These essays appeared shortly after Galileo's condemnation and Descartes' decision not to publish his magnum opus, Le monde (The World). The importance of the Discourse, in conjunction with the Mediations, can hardly be overstated.

1638 -- Galileo's second major book, the Discours on Two New Sciences, was published outside of Italy in Protestant Leiden. The work drew together much of Galileo's earlier efforts on the problem of motion; the second 'new science' (where Galileo, in retrospect, was less successful) dealt with the strength of materials.

The Englishman John Wilkins (1614-1672) published his Discovery of a World in the Moone, a curious work that drew together many of the findings of Kepler and Galileo into an imaginative landscape. Aimed at what might be called the general reader, Wilkin's book (perhaps like Kepler's The Dream) lays claim to one of the earliest writings in 'science fiction'.

1639 -- The first observation of a transit of Venus across the Sun, a rare phenomenon used in the eighteenth and nineteenth centuries for determining the distance of the earth from the Sun, is made by the brilliant but short-lived Jeremiah Horrocks (1618-1641) at Toxteth Park near Liverpool. Few others offered observations of this telling event, as sky conditions were not favorable on the continent, certainly not in France.

1641 -- René Descartes' Meditations presents his famous (or infamous) 'grand bi-furcation of the universe', that is, his dualistic metaphysical belief in res cogitans (mind) and res extensa (matter), the foundational belief of mechanistic natural philosophy.

1644 -- The Italian physicist and mathematician Evangelista Torricelli (1608-1647), having filled a sealed tube with mercury, and with the open end immersed in mercury, noted that the height fell in the tube to a consistent level, leaving a void above it. The problem was addressed by a number of members of the Cimento and challenges to explain the phenomenon were sent to others outside of Italy.

René Descartes' Principles of Philosophy supplies arguments for the Mechanical Philosophy, most notably that the Universe is filled with uniform matter and united across space and time by uniform principles of motion and hence mechanical forms (contact, impact, pressure) of causation.

1645 -- Publication of Ismaël Boulliau's (1605-1694) Philolaic Astronomy, perhaps the most influential work published between Kepler and Newton. The large folio volume is widely cited for promoting acquaintance with Kepler's elliptical planetary paths. For all that, Boulliau roundly rejected Kepler's peculiar mix of ideas concerning the physical causes of the planetary motions.

Michael Florentz van Langren (1598-1675) published a short work that presented one of the first engraved lunar maps accompanied by a system of nomenclature (mostly aimed at obtaining patronage and gaining friendships).

1647 -- A much more detailed description with illustrations of the surface features of the Moon is given by Johannes Hevelius (1611-1687) in his Selenographia. Unlike van Langren, Hevelius chooses to avoid naming lunar features in honor of those still living.

Otto von Guericke (1602-1686 constructed was it believed to be the first air pump.

Blaise Pascal's (1623-1662) New Experiments Concerning the Void describes observations concerning the Torricelli mercury tube, arguing that the presence of matter above certain liquids (spirits) cannot be detected, that is, that the existence of a void cannot be demonstrated by experiment.

1648 -- Jan Baptista van Helmont (1579-1644) argues for medical chemistry and the view that 'chemistry' is central to understanding physiology.

Oxford Philosophical Society meets for the first time; the group is experimental in approach, and by tradition this group may have been instrumental in establishing the Royal Society of London.

1651 -- A self-described student of geometry, atomism, and optics, Thomas Hobbes's (1588-1679) published his classic work on political theory, The Leviathan, which seems to have reflected notions evident in his study of natural phenomena, most notably mechanistic concepts relating to physiology and sensation. Famously, Hobbes held human life 'solitary, poor, nasty, brutish, and short'.

A competent astronomer, the Jesuit Giovanni Battista Riccioli (1598-1671) published his massive New Almagest, a work that treated the efforts of both Copernicus and Kepler but which sought to show that the earth does not move.

1653 -- In Paris, the first meetings of the Montmor Academy take place, signaling one of the most important French semi-private scientific societies. The group evolved rapidly under its patron, 'Montmor the Rich', H. L. Habert de Montmor (c.1600-1679). Several members of the group, most famously Huygens, most notorious Roberval, were appointed the Académie des Sciences.

Christiaan Huygens applies the sine law of refraction to spherical lenses.

1654 -- Walter Charleton's (1620-1707) presents atomism to the English in his highly influential work, Physiologia Epicuro-Gassendo-Charletoniana, a paraphrase, sometimes a caricature, of the ideas present by Pierre Gassendi. It now seems likely that this is the major source of Newton's information about Gassendi's work on atomism and the Frenchman's views on the probable character of knowledge.

James Ussher (1581-1656), a Biblical scholar who argued, having analyzed Holy Writ, that the date of Creation was 23 October 4004 B.C., apparently at 9.00am. With simian mirth, the defending lawyer in the Scope's Monkey Trial was unable to discover if the time was GMT or perhaps EDT.

1656 -- Christiaan Huygens' pendulum clock opens the possibility of determining the equation of time directly, which would side-step key difficulties associated with a key problem of planetary theory, solar parallax.

1657 -- Founding of the Accademia del Cimento (Academy of Experiments) in Florence under the auspices of Prince Leopold of Tuscany and his brother, Ferdinando II; the Accademia thrived for about a decade but with fewer than half-a-dozen active participants, chief among them Borelli.

Otto von Guericke (1602-1686) demonstrates the pressure of air by showing that teams of horses could not pull apart two metal hemispheres from which air had been removed, the outside air, he concluded, pressed the two hemispheres immovably together.

1658 -- Christiaan Huygens provides still further information on his improved but still controversial pendulum clock yielding a substantial increase in accuracy, now a matter of seconds per day.

Publication of a detailed exposition of Epicurean philosophy by Pierre Gassendi which incorporates Christian elements and aspects of atomism. The result has been called Gassendi's 'baptism of Epicurus'.

1659 -- Huygens explains the changing appearances of Saturn as due to its being surrounded by a flat, thin ring of matter. Controversy continued regarding how the appearances were to be explained and, perhaps more importantly, concerning the details of Saturn's inclination and the periodicity of its cycle.

1661 -- The Italian Marcello Malpighi (1628-1694) uses the microscope to observes capillaries joining arteries and veins. Malpighi showed in fine detail that blood circulates.

In his Sceptical Chymst Robert Boyle argues for experiment against Aristotelian and Paracelsian practitioners, and distinguishes acids and bases.

1662 -- René Descartes' Treatise on Man is published posthumously arguing that human anatomy and physiology can be understood by means of mechanical principles.

The Royal Society of London is established by royal charter, and several key appointments are made, Robert Hooke (1635-1702) as Curator of Experiments, and later, Henry Oldenburg, as First Secretary.

The Englishman John Graunt (1620-1674) in conjunction with the work of William Petty publishes his Observations upon the Bills of Mortality with data drawn from London's population; life expectancy from birth is approximately 27 years with nearly 2/3 of the population dying before the age of 16.

1664 -- René Descartes' The World, published 14 years after his death, present a theory whereby light is transmitted as pressure (a 'wave front') in a medium (consisting of a "subtle matter") that operates by contact, impact, and pressure. Descartes distinguishes between light 'as body' and light that we 'see' by suggesting that two different explanations be provided for the same phenomenon.

1665 -- In Paris the Journal des Sçavans is published for the first time, the first journal to feature scientific news, reviews and summaries of book, eulogies, and occasional editorials. The first publication of the Philosophical Transactions of London, were initiated as a private venture by Henry Oldenburg.

In optics, Francesco Maria Grimaldi (1618-1663) describes diffraction of light and proposes a theory to account for how light fails to move in a straight line, most notably as it passes the edge of certain bodies.

Robert Hooke (1635-1702) publishes his famous Micrographia, which includes useful and stunning etchings of his microscopic observations, the most famous, perhaps, Hooke's flea.

1666 -- In his Theories of the Medicean Planets G-A Borelli's (1608-1679) argues that planetary orbits result from an innate attraction to their centers and from a quasi-inertial tendency to remain in motion; it is a curious mix, as Borelli also argues that the two tendencies that give rise to planetary motion are somehow 'balanced'.

In Paris the Académie des Sciences is established under the direction of Colbert and the direct patronage of King Louis XIV. Unlike the Royal Society of London, the French academy is based on funded appointments rather than by paying members who propose and elect new members.

Robert Boyle in his Origines of Formes and Qualities seeks to explain chemical change by means of "corpuscularianism" (small bodies), thereby extending the influence of the mechanical philosophy.

1667 -- The Paris Observatory, called for by Auzout and others, is finally established by means of royal patronage; the design is controversial, devised by Perrault, with plans that the building be used not only for astronomical observation but for experiments, meetings, and storing apparatus and various collections.

1668 -- In his Experiments on the Generation of Insects the noted Italian Francesco Redi (1626-1679) showed that insects and other forms of life are not generated spontaneously.

1669 -- Isaac Newton (1642-1727) builds his first reflecting telescope; the design, which includes an eyepiece and a concave mirror, is known today as 'Newtonian'.

Isaac Barrow (1630-1677), first to occupy the Lucasian Chair of Mathematics at Cambridge University, resigns, by tradition, in favor of young Isaac Newton.

Jan Swammerdam's (1637-1680) microscopical work on insects leads him to reject spontaneous generation and to speculate whether organisms are fully formed before fetal development.

1670 -- Newton concentrated and sustained interest in alchemy.

1671 -- Jacques Rohault's (1618-1672) Traité de Physique (Treatise on Physics) published as an important text on Cartesian natural philosophy.

Jean Picard (1620-1682) publishes his seminal work, Mesure de la terre (Measure of the Earth), which provides a lucid account and precise measurements for the length of a meridian; Picard's work with the pendulum clock later proved of great importance to Newton in speculating about the shape of the earth.

1672 -- In his first major publication, Isaac Newton (in the Philosophical Transactions) established by means of experiment that white light was not one and pure, but rather that white light was mixed and heterogeneous: white light, against tradition, was in fact composed of a spectrum of colors (the rainbow) and each color is the result of a measurable angle of bending (refraction). Color as a quality was, according to tradition, a quantifiable degree of refrangibility.

Marcello Malpighi (1628-1694) made rigorous microscopic observation of the embryonic development of the chick and the early formation of organs.

1672-1673 -- Jean Richer's (1630-1696) expedition to Cayenne (in French Guyana) results in an adjustment in the obliquity of the ecliptic and the value assigned to horizontal solar parallax, a critical constant in planetary theory.

1673 -- Christiaan Huygens published yet another study of the pendulum clock, the brilliant and mature essay, Horologium oscillatorium (The oscillation of pendula).

1674 -- John Mayow (1641-1679) proposes that certain particles in the air are necessary for combustion and are transmitted by the lungs to the blood.

1675 -- Ole Roemer uses astronomical observations to derived the speed of light, which he demonstrates is finite.

Gian Domenico Cassini (1625-1712) discovers a gap in the ring system of Saturn, demonstrating that the ring is not a uniform and flat disk.

The Royal Observatory at Greenwich is established by Charles II and the first Royal Astronomer, John Flamsteed (1646-1719), is appointed director.

Robert Boyle proposes in his Experiments and Notes about the Mechanical Origin and Production of Electricity that electrical effects can be explained by the emission and refraction of electrical effluvia.

In London Thomas Shadwell's The Virtuoso satirizes the work of the Royal Society as silly and impractical, thereby rivaling scorn for that institution delivered by Jonathan Swift.

1677 -- Antoni van Leeuwenhoek observes of spermatozoa by means of the microscope, arguing they are not forms of disease but a source of reproductive material.

1678 -- One of the 'Cambridge Platonists', Ralph Cudworth (1617-1688), in his True intellectual System of the Universe, strongly challenges on theological grounds the notion that the world ultimately consists inert matter -- Cudworth suggests the idea of 'plastic nature'..

Edmond Halley (1646-1743) presents a catalogue of the stars in the Southern Hemisphere.

The Curator of Experiments presents "Hooke's Law" which states that the "power" of a spring is proportional to its tension.

1679 -- The Danzig astronomer Johannes Hevelius describes his instruments and provides one of the most extensive catalogues of the period.

Edme Mariotte (c.1620-1684) of the French Académie des Sciences describes the motion of sap in plants as circulating, apparently on the analogy of the circulation of blood.

Robert Hooke wrote a legendary letter asking Newton's opinion on the possibility of explaining the motions of the planets on the assumption of inertia and an attractive power from the sun. This heroic exchange of letters led to a legendary series of events (see Halley, 1684 below) resulting, according to tradition, in Newton's Mathematical Principles of Natural Philosophy (1687).

1681 -- Giovanni Alfonso Borelli (1608-1689) employs mechanical principles in his analysis of animal movement in his posthumously published De motu animalum (On the Motions of Animals).

Thomas Burnet's (1635-1715) Sacred Theory of the Earth treats the changing character of the earth's surface while following the basic lines of biblical chronology.

1683 -- The Ashmolean Museum (Oxford) is established as the first public museum in England, its founder, Elias Ashmole (1617-1692) supplies his collections and library.

1684 -- Gian Domenico Cassini (1625-1712) observes the third and fourth satellites of Saturn (Dione and Thetys), which compliment those first observed in 1671 and 1672.

In mathematics, Gottfried Wilhelm Leibniz's (1646-1716) publishes his first paper which supplies forms of notation for the calculus of infinitesimals.

1686 -- Publication of the first edition of Conversations on the Plurality of Worlds by Bernard le Bovier de Fontenelle (1657-1757), later the perpetual secretary of Académie des Sciences, a classic popularization of the Cartesian vortices and Copernican cosmology. Notably, the conversation that unfolds in a garden is between a man and a woman.

Gottfried Wilhelm Leibniz (1646-1716) asserts against René Descartes that the measure of force is not mv but to mv2, which heightens the so-called vis viva (= 'living force") controversy.

1687 -- Arguably the most seminal work of the century, Isaac Newton's Mathematical Principles of Natural Philosophy proposes foundational principles for what has come to known as classical mechanics; by tradition, Newton established a new set of 'mental categories' now associated with the concepts of force, mass, acceleration as evidenced in three 'laws of motion' and principle of universal gravitation.

1690 -- In his Essay Concerning Human Understanding John Locke (1632-1704), a fried of Newton, argues that knowledge of the nature is probable, not certain, and is rooted in sense experience, not innate ideas.

William Petty's (1623-1687) pioneering Political Arithmetic develops mathematical methods as a foundation for political economy.

In his Treatise on Light Christiaan Huygens proposes a wave theory (against Newton's particulate theory) for the propagation of light.

1693 -- Edmond Halley provides a mathematical equation for finding the focal lengths of lenses of all shapes.

1696 -- Publication of the first textbook on the calculus by the Marquis de L'Hôpital (1661-1704).

1697 -- Samuel Clarke (1618-1672) translates Jacques Rohault's Cartesian Traité de physique (Treatise on Physics, 1671) as System of Natural Philosophy, which is widely used as a university textbook.

1700 -- Gottfried Wilhelm von Leibniz organizes and establishes the Berlin Academy of Science.

1702 -- Publication of David Gregory's (1659-1708) 'Newtonian' Astronomiae physicae et geometriae elemenata (Elements of Physical and Geometrical Astronomy), with contains an anonymous preface by Newton.

1703 -- March 3 - Robert Hooke dies; Newton decides to go forward in publishing his work on optics; November 30 - Newton is elected President of Royal Society

1704 -- Isaac Newton (1642-1727) publishes the first edition of his Opticks, based on work done during his days a Cambridge, including a series of speculations about nature and natural philosophy under enumerated as "Queries".

1705 -- The comet that now bears Edmond Halley's name (which he observed in 1682) is determined by him to have an elongated elliptical orbit, and therefore argued it should submit to Newtonian principles.

April 16, Newton is Knighted by Queen Anne in Cambridge, thereafter, he is known as Sir Isaac Newton.

1706 -- Publication of the first Latin edition of Newton's Opticks with its Queries

1712 -- Publication of John Flamsteed's Historia coelestis Britannica, which contains positions for some 3000 stars, more than three times that of Tycho's catalogue.

1713 -- William Derham's (1657-1735) Physico-theology, and the second revised edition of Newton's Principia (containing an introduction by Roger Cotes) suggest a movement to use the findings of science as evidence for 'Design' and hence as evidence for the 'Designer'.

1715 -- Gottfried Wilhelm von Leibniz sends objections to Newton's philosophy to the Princess of Wales which sparks controversy between Leibniz and Samuel Clarke, Newton's representative, on the issue of God's relation to a mechanical universe ('Clockmaker'- Clockwork).

1717 -- Newton publishes second English edition of Opticks with eight queries

1725 -- May 27 - Newton refuses to grant publication of Short Chronology but publishes it later that year. Newton suffers inflammation of his lungs and moves to Kensington (south London).

1727 -- March 18 - Newton's health fails, he collapses and borders on death; shortly thereafter, Newton dies at Kensington between 1.00 and 2.00am. On 28 March his body lays in state in Westminster Abbey where he is buried on 4 April.

1733 -- Newton's Observations Upon the Prophecies is published (London); some eleven printings follow.

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