Tychonic system

The Tychonic system (or Tychonian system) is a model of the Solar System published by Tycho Brahe in the late 16th century, which combines what he saw as the mathematical benefits of the Copernican system with the philosophical and "physical" benefits of the Ptolemaic system. The model may have been inspired by Valentin Naboth[1] and Paul Wittich, a Silesian mathematician and astronomer.[2] A similar model was implicit in the calculations a century earlier by Nilakantha Somayaji of the Kerala school of astronomy and mathematics.[3][4]

It is conceptually a geocentric model: the Earth is at the centre of the universe, the Sun and Moon and the stars revolve around the Earth, and the other five planets revolve around the Sun. At the same time, the motions of the planets are mathematically equivalent to the motions in Copernicus' heliocentric system under a simple coordinate transformation, so that, as long as no force law is postulated to explain why the planets move as described, there is no mathematical reason to prefer either the Tychonic or the Copernican system.[5]

A 17th century illustration of the Hypothesis Tychonica from Hevelius' Selenographia, 1647 page 163, whereby the Sun, Moon, and sphere of stars orbit the Earth, while the five known planets (Mercury, Venus, Mars, Jupiter, and Saturn) orbit the Sun.
Tychonian system
The Tychonic system shown in colour, with the objects that rotate around the Earth shown on blue orbits, and the objects that rotate around the Sun shown on orange orbits. Around all is a sphere of stars, which rotates.

Motivation for the Tychonic system

Tycho admired aspects of Copernicus's heliocentric model of the Solar System, but felt that it had problems as concerned physics, astronomical observations of stars, and religion. Regarding the Copernican system, Tycho wrote,

This innovation 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.[6]

In regard to physics, Tycho held that the Earth was just too sluggish and heavy to be continuously in motion. According to the accepted Aristotelian physics of the time, the heavens (whose motions and cycles were continuous and unending) were made of "Aether" or "Quintessence"; this substance, not found on Earth, was light, strong, and unchanging, and its natural state was circular motion. By contrast, the Earth (where objects seem to have motion only when moved) and things on it were composed of substances that were heavy and whose natural state was rest. Consequently, the Earth was considered to be a "lazy" body that was not readily moved.[7] Thus while Tycho acknowledged that the daily rising and setting of the Sun and stars could be explained by the Earth's rotation, as Copernicus had said, still

such a fast motion could not belong to the earth, a body very heavy and dense and opaque, but rather belongs to the sky itself whose form and subtle and constant matter are better suited to a perpetual motion, however fast.[8]

In regards to the stars, Tycho 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 thanks to Earth's changing position (this parallax does exist, but is so small it was not detected until 1838, when Friedrich Bessel discovered a parallax of 0.314 arcseconds of the star 61 Cygni[9]). The Copernican explanation for this lack of parallax was that the stars were such a great distance from Earth that Earth's orbit was almost insignificant by comparison. However, Tycho noted that this explanation introduced another problem: Stars as seen by the naked eye appear small, but of some size, with more prominent stars such as Vega appearing larger than lesser stars such as Polaris, which in turn appear larger than many others. Tycho had determined that a typical star measured approximately a minute of arc in size, with more prominent ones being two or three times as large.[10] In writing to Christoph Rothmann, a Copernican astronomer, Tycho used basic geometry to show that, assuming a small parallax that just escaped detection, the distance to the stars in the Copernican system would have to be 700 times greater than the distance from the sun to Saturn. Moreover, the only way the stars could be so distant and still appear the sizes they do in the sky would be if even average stars were gigantic—at least as big as the orbit of the Earth, and of course vastly larger than the sun. (As a matter of fact, most stars visible to the naked eye are giants, supergiants, or large, bright main-sequence stars.) And, Tycho said, the more prominent stars would have to be even larger still. And what if the parallax was even smaller than anyone thought, so the stars were yet more distant? Then they would all have to be even larger still.[11] Tycho said

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.[12]

Copernicans offered a religious response to Tycho's geometry: titanic, distant stars might seem unreasonable, but they were not, for the Creator could make his creations that large if he wanted.[13] In fact, Rothmann responded to this argument of Tycho's by saying

[W]hat is so absurd about [an average star] having size equal to the whole [orbit of the Earth]? What of this is contrary to divine will, or is impossible by divine Nature, or is inadmissible by infinite Nature? These things must be entirely demonstrated by you, if you will wish to infer from here anything of the absurd. These things that vulgar sorts see as absurd at first glance are not easily charged with absurdity, for in fact divine Sapience and Majesty is far greater than they understand. Grant the vastness of the Universe and the sizes of the stars to be as great as you like—these will still bear no proportion to the infinite Creator. It reckons that the greater the king, so much greater and larger the palace befitting his majesty. So how great a palace do you reckon is fitting to GOD?[14]

Religion played a role in Tycho's geocentrism also—he cited the authority of scripture in portraying the Earth as being at rest. He rarely used Biblical arguments alone (to him they were a secondary objection to the idea of Earth's motion) and over time he came to focus on scientific arguments, but he did take Biblical arguments seriously.[15]

Tycho advocated as an alternative to the Ptolemaic geocentric system a "geoheliocentric" system (now known as the Tychonic system), which he developed in the late 1570s. In such a system, the Sun, Moon, and stars circle a central Earth, while the five planets orbit the Sun.[16] The essential difference between the heavens (including the planets) and the Earth remained: Motion stayed in the aethereal heavens; immobility stayed with the heavy sluggish Earth. It was a system that Tycho said violated neither the laws of physics nor sacred scripture—with stars located just beyond Saturn and of reasonable size.[17][18]

Precursors to geoheliocentrism

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.[19] Macrobius Ambrosius Theodosius (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.[20][21] 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.[22][23] 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.

History and development

Tycho's system was foreshadowed, in part, by that of Martianus Capella, who described a system in which Mercury and Venus are placed on epicycles around the Sun, which circles the Earth. Copernicus, who cited Capella's theory, even mentioned the possibility of an extension in which the other three of the six known planets would also circle the Sun.[24] This was foreshadowed by the Irish Carolingian scholar Johannes Scotus Eriugena in the 9th century, who went a step further than Capella by suggesting both Mars and Jupiter orbited the sun as well.[25] In the 15th century, his work was anticipated by Nilakantha Somayaji, an Indian astronomer of the Kerala school of astronomy and mathematics, who first presented a geoheliocentric system where all the planets (Mercury, Venus, Mars, Jupiter and Saturn) orbit the Sun, which in turn orbits the Earth.[3][4][26]

The Tychonic system, which was announced in 1588,[27] became a major competitor with the Copernican system as an alternative to the Ptolemaic. After Galileo's observation of the phases of Venus in 1610, most cosmological controversy then settled on variations of the Tychonic and Copernican systems. In a number of ways, the Tychonic system proved philosophically more intuitive than the Copernican system, as it reinforced commonsense notions of how the Sun and the planets are mobile while the Earth is not. Additionally, a Copernican system would suggest the ability to observe stellar parallax, which could not be observed until the 19th century. On the other hand, because of the intersecting deferents of Mars and the Sun (see diagram), it went against the Ptolemaic and Aristotelian notion that the planets were placed within nested spheres. Tycho and his followers revived the ancient Stoic philosophy instead, since it used fluid heavens which could accommodate intersecting circles.


After Tycho's death, Johannes Kepler used the observations of Tycho himself to demonstrate that the orbits of the planets are ellipses and not circles, creating the modified Copernican system that ultimately displaced both the Tychonic and Ptolemaic systems. However, the Tychonic system was very influential in the late 16th and 17th centuries. In 1616, during the Galileo affair, the papal Congregation of the Index banned all books advocating the Copernican system, including works by Copernicus, Galileo, Kepler and other authors until 1758.[28][29] The Tychonic system was an acceptable alternative as it explained the observed phases of Venus with a static Earth. Jesuit astronomers in China used it, as did a number of European scholars. Jesuits (such as Clavius, Christoph Grienberger, Christoph Scheiner, Odo Van Maelcote) supported the Tychonic system. [30]

The discovery of stellar aberration in the early 18th century by James Bradley proved that the Earth did in fact move around the Sun and Tycho's system fell out of use among scientists.[31] In the modern era, some of the modern geocentrists use a modified Tychonic system with elliptical orbits, while rejecting the concept of relativity.[32][33]

See also


  1. ^ Westman, Robert S. (1975). The Copernican achievement. University of California Press. p. 322. ISBN 978-0-520-02877-7. OCLC 164221945.
  2. ^ Owen Gingerich, The Book Nobody Read: Chasing the Revolutions of Nicolaus Copernicus, Penguin, ISBN 0-14-303476-6
  3. ^ a b Ramasubramanian, K. (1994). "Modification of the earlier Indian planetary theory by the Kerala astronomers (c. 1500 AD) and the implied heliocentric picture of planetary motion" (PDF). Current Science. 66: 784–90.
  4. ^ a b Joseph, George G. (2000), The Crest of the Peacock: Non-European Roots of Mathematics, p. 408, Princeton University Press, ISBN 978-0-691-00659-8
  5. ^ "The Tychonic system is, in fact, precisely equivalent mathematically to Copernicus' system." (p. 202) and "[T]he Tychonic system is transformed to the Copernican system simply by holding the sun fixed instead of the earth. The relative motions of the planets are the same in both systems ..." (p. 204), Kuhn, Thomas S. , The Copernican Revolution (Harvard University Press, 1957).
  6. ^ Owen Gingerich, The eye of heaven: Ptolemy, Copernicus, Kepler, New York: American Institute of Physics, 1993, 181, ISBN 0-88318-863-5
  7. ^ Blair, Ann, "Tycho Brahe's critique of Copernicus and the Copernican system", Journal of the History of Ideas, 51, 1990: 355–377, doi:10.2307/2709620, pages 361–362. Moesgaard, Kristian Peder, "Copernican Influence on Tycho Brahe", The Reception of Copernicus' Heliocentric Theory (Jerzy Dobrzycki, ed.) Dordrecht & Boston: D. Reidel Pub. Co. 1972. ISBN 90-277-0311-6, page 40. Gingerich, Owen, "Copernicus and Tycho", Scientific American 173, 1973: 86–101, page 87.
  8. ^ Blair, 1990, 361.
  9. ^ J J O'Connor and E F Robertson. Bessel biography. University of St Andrews. Retrieved 2008-09-28
  10. ^ The sizes Tycho measured turned out to be illusory – an effect of optics, the atmosphere, and the limitations of the eye (see Airy disk or Astronomical seeing for details). By 1617, Galileo estimated with the use of his telescope that the largest component of Mizar measured 3 seconds of arc, but even that turned out to be illusory – again an effect of optics, the atmosphere, and the limitations of the eye [see L. Ondra (July 2004). "A New View of Mizar". Sky & Telescope: 72–75.]. Estimates of the apparent sizes of stars continued to be revised downwards, and, today, the star with the largest apparent size is believed to be R Doradus, no larger than 0.057 ± 0.005 seconds of arc.
  11. ^ Blair, 1990, 364. Moesgaard, 1972, 51.
  12. ^ Blair, 1990, 364.
  13. ^ Moesgaard, 1972, 52. Vermij R., "Putting the Earth in Heaven: Philips Lansbergen, the early Dutch Copernicans and the Mechanization of the World Picture", Mechanics and Cosmology in the Medieval and Early Modern Period (M. Bucciantini, M. Camerota, S. Roux., eds.) Firenze: Olski 2007: 121–141, pages 124–125.
  14. ^ Graney, C. M., "Science Rather Than God: Riccioli's Review of the Case for and Against the Copernican Hypothesis", Journal for the History of Astronomy 43, 2012: 215–225, page 217.
  15. ^ Blair, 1990, 362–364
  16. ^ Gingerich, 1973. Moesgaard, 1972, 40–43.
  17. ^ Moesgaard 40, 44
  18. ^ Graney, C. M. (March 6, 2012). The Prof says: Tycho was a scientist, not a blunderer and a darn good one too! The Renaissance Mathematicus. http://thonyc.wordpress.com/2012/03/06/the-prof-says-tycho-was-a-scientist-not-a-blunderer-and-a-darn-good-one-too/
  19. ^ Eastwood, B. S. (1992-11-01). "Heraclides and Heliocentrism – Texts Diagrams and Interpretations". Journal for the History of Astronomy. 23: 233. Bibcode:1992JHA....23..233E.
  20. ^ Neugebauer, Otto E. (1975). A history of ancient mathematical astronomy. Birkhäuser. ISBN 3-540-06995-X.
  21. ^ Rufus, W. Carl (1923). "The astronomical system of Copernicus". Popular Astronomy. 31: 510–521 [512]. Bibcode:1923PA.....31..510R.
  22. ^
  23. ^ George G. Joseph (2000). The Crest of the Peacock: Non-European Roots of Mathematics, p. 408. Princeton University Press.
  24. ^ [1]
  25. ^ Stanford Encyclopedia of Philosophy. "John Scottus Eriugena." First published Thu Aug 28, 2003; substantive revision Sun Oct 17, 2004. Accessed April 30, 2014.
  26. ^ Ramasubramanian, K., "Model of planetary motion in the works of Kerala astronomers", Bulletin of the Astronomical Society of India, 26: 11–31 [23–4], Bibcode:1998BASI...26...11R, retrieved 2010-03-05
  27. ^ Hatch, Robert. "EARLY GEO-HELIOCENTRIC MODELS". The Scientific Revolution. Dr. Robert A. Hatch. Retrieved 11 April 2018.
  28. ^ Finochiario, Maurice (2007). Retrying Galileo. University of California Press.
  29. ^ Heilbron (2010), pp. 218–9
  30. ^ Pantin, Isabelle (1999). "New Philosophy and Old Prejudices: Aspects of the Reception of Copernicanism in a Divided Europe". Stud. Hist. Phil. Sci. 30 (237–262): 247.
  31. ^ Seligman, Courtney. Bradley's Discovery of Stellar Aberration. (2013). http://cseligman.com/text/history/bradley.htm
  32. ^ Plait, Phil. (Sept. 14, 2010). Geocentrism Seriously? Discover Magazine. http://blogs.discovermagazine.com/badastronomy/2010/09/14/geocentrism-seriously/#.UVEn7leiBpd
  33. ^ Musgrave, Iam. (Nov. 14, 2010). Geo-xcentricities part 2; the view from Mars. Astroblog. http://astroblogger.blogspot.com/2010/11/geo-xcentricities-part-2-view-from-mars.html

External links

Astronomia nova

Astronomia nova (English: New Astronomy, full title in original Latin: Astronomia Nova ΑΙΤΙΟΛΟΓΗΤΟΣ seu physica coelestis, tradita commentariis de motibus stellae Martis ex observationibus G.V. Tychonis Brahe) is a book, published in 1609, that contains the results of the astronomer Johannes Kepler's ten-year-long investigation of the motion of Mars. One of the most significant books in the history of astronomy, the Astronomia nova provided strong arguments for heliocentrism and contributed valuable insight into the movement of the planets. This included the first mention of the planets' elliptical paths and the change of their movement to the movement of free floating bodies as opposed to objects on rotating spheres. It is recognized as one of the most important works of the scientific revolution.

Christen Sørensen Longomontanus

Christen Sørensen Longomontanus (or Longberg) (4 October 1562 – 8 October 1647) was a Danish astronomer.

The name Longomontanus was a Latinized form of the name of the village of Lomborg, Jutland, Denmark, where he was born. His father, a laborer called Søren, or Severin, died when Christen was eight years old. An uncle took charge of the child, and had him educated at Lemvig; but after three years sent him back to his mother, who needed his help to work the fields. She agreed that he could study during the winter months with the clergyman of the parish; this arrangement continued until 1577, when the ill-will of some of his relatives and his own desire for knowledge caused him to run away to Viborg.

There he attended the grammar school, working as a labourer to pay his expenses, and in 1588 went to Copenhagen with a high reputation for learning and ability. Engaged by Tycho Brahe in 1589 as his assistant in his great astronomical observatory of Uraniborg, he rendered invaluable service for eight years. Having left the island of Hven with his master, he obtained his discharge at Copenhagen on 1 June 1597, in order to study at some German universities. He rejoined Tycho at Prague in January 1600, and having completed the Tychonic lunar theory, turned homeward again in August.

He visited Frauenburg, where Copernicus had made his observations, took a master's degree at Rostock, and at Copenhagen found a patron in Christian Friis, chancellor of Denmark, who employed him in his household. Appointed in 1603 rector of the school of Viborg, he was elected two years later to a professorship in the University of Copenhagen, and his promotion to the chair of mathematics ensued in 1607. This post was held by Longomontanus till his death in 1647.

Longomontanus was not an advanced thinker. He adhered to Tycho's erroneous views about refraction, believed that comets were messengers of evil, and imagined that he had squared the circle. He found that the circle whose diameter is 43 has for its circumference the square root of 18252 which gives 3.14185... (or ​22⁄7) for the value of π. John Pell and others tried in vain to convince him of his error. In 1632 he started the construction of the Rundetårn (a stately astronomical tower in Copenhagen), but did not live to witness its completion. King Christian IV of Denmark, to whom he dedicated his Astronomia Danica, an exposition of the Tychonic system of the universe, conferred upon him the canonry of Lunden in Schleswig.

Longomontanus's major contribution to science was to develop Tycho's geoheliocentric model of the universe empirically and publicly to common acceptance.

When Tycho died in 1601, his program for the restoration of astronomy was unfinished. The observational aspects were complete, but two important tasks remained, namely the selection and integration of the data into accounts of the motions of the planets, and the presentation of the results on the entire program in the form of a systematic treatise. Longomontanus assumed the responsibility and fulfilled both tasks in his voluminous Astronomia Danica (1622). Regarded as the testament of Tycho, the work was eagerly received in seventeenth-century astronomical literature. But unlike Tycho's, the geoheliocentric model of Longomontanus gave the Earth a proper daily rotation (as in the models of Ursus and Roslin). It is therefore sometimes called the 'semi-Tychonic' system.

The book was reprinted in 1640 and 1663, which inidcates its popularity and the interest in the semi-Tychonic system in this period.

Having originally worked on calculating the Martian orbit for Tycho with Kepler, he had already modelled its orbit in his geoheliocentric model to an error in longitude of under 2 arcminutes when Kepler had still only achieved 8 arcminutes error in his heliocentric system, as he had not yet used elliptical orbits.

Some historians claim Kepler’s 1627 Rudolphine Tables, based on Tycho Brahe’s observations, were more accurate than any previous tables. But nobody has ever demonstrated they were more accurate than Longomontanus’s 1622 Danish Astronomy tables, also based upon Tycho’s observations.


Cosmology (from the Greek κόσμος, kosmos "world" and -λογία, -logia "study of") is a branch of astronomy concerned with the studies of the origin and evolution of the universe, from the Big Bang to today and on into the future. It is the scientific study of the origin, evolution, and eventual fate of the universe. Physical cosmology is the scientific study of the universe's origin, its large-scale structures and dynamics, and its ultimate fate, as well as the laws of science that govern these areas.The term cosmology was first used in English in 1656 in Thomas Blount's Glossographia, and in 1731 taken up in Latin by German philosopher Christian Wolff, in Cosmologia Generalis.Religious or mythological cosmology is a body of beliefs based on mythological, religious, and esoteric literature and traditions of creation myths and eschatology.

Physical cosmology is studied by scientists, such as astronomers and physicists, as well as philosophers, such as metaphysicians, philosophers of physics, and philosophers of space and time. Because of this shared scope with philosophy, theories in physical cosmology may include both scientific and non-scientific propositions, and may depend upon assumptions that cannot be tested. Cosmology differs from astronomy in that the former is concerned with the Universe as a whole while the latter deals with individual celestial objects. Modern physical cosmology is dominated by the Big Bang theory, which attempts to bring together observational astronomy and particle physics; more specifically, a standard parameterization of the Big Bang with dark matter and dark energy, known as the Lambda-CDM model.

Theoretical astrophysicist David N. Spergel has described cosmology as a "historical science" because "when we look out in space, we look back in time" due to the finite nature of the speed of light.

Dialogue Concerning the Two Chief World Systems

The Dialogue Concerning the Two Chief World Systems (Dialogo sopra i due massimi sistemi del mondo) is a 1632 Italian-language book by Galileo Galilei comparing the Copernican system with the traditional Ptolemaic system. It was translated into Latin as Systema cosmicum (English: Cosmic System) in 1635 by Matthias Bernegger. The book was dedicated to Galileo's patron, Ferdinando II de' Medici, Grand Duke of Tuscany, who received the first printed copy on February 22, 1632.In the Copernican system, the Earth and other planets orbit the Sun, while in the Ptolemaic system, everything in the Universe circles around the Earth. The Dialogue was published in Florence under a formal license from the Inquisition. In 1633, Galileo was found to be "vehemently suspect of heresy" based on the book, which was then placed on the Index of Forbidden Books, from which it was not removed until 1835 (after the theories it discussed had been permitted in print in 1822). In an action that was not announced at the time, the publication of anything else he had written or ever might write was also banned in Catholic countries.

Discourse on the Tides

"Discourse on the Tides" (Italian: Discorso Sul Flusso E Il Reflusso Del Mare) is an essay written by Galileo Galilei in 1616 as a letter to Alessandro Orsini that attempted to explain the motion of Earth's tides as a consequence of Earth's rotation and revolution around the Sun. The same ideas form an important part of Galileo's Dialogue Concerning the Two Chief World Systems. Galileo's theory was in fact erroneous, as proven by future scientific research.

Galileo Galilei

Galileo Galilei (Italian: [ɡaliˈlɛːo ɡaliˈlɛi]; 15 February 1564 – 8 January 1642) was an Italian astronomer, physicist and engineer, sometimes described as a polymath. Galileo has been called the "father of observational astronomy", the "father of modern physics", the "father of the scientific method", and the "father of modern science".Galileo studied speed and velocity, gravity and free fall, the principle of relativity, inertia, projectile motion and also worked in applied science and technology, describing the properties of pendulums and "hydrostatic balances", inventing the thermoscope and various military compasses, and using the telescope for scientific observations of celestial objects. His contributions to observational astronomy include the telescopic confirmation of the phases of Venus, the observation of the four largest satellites of Jupiter, the observation of Saturn and the analysis of sunspots.

Galileo's championing of heliocentrism and Copernicanism was controversial during his lifetime, when most subscribed to geocentric models such as the Tychonic system. He met with opposition from astronomers, who doubted heliocentrism because of the absence of an observed stellar parallax. The matter was investigated by the Roman Inquisition in 1615, which concluded that heliocentrism was "foolish and absurd in philosophy, and formally heretical since it explicitly contradicts in many places the sense of Holy Scripture". Galileo later defended his views in Dialogue Concerning the Two Chief World Systems (1632), which appeared to attack Pope Urban VIII and thus alienated him and the Jesuits, who had both supported Galileo up until this point. He was tried by the Inquisition, found "vehemently suspect of heresy", and forced to recant. He spent the rest of his life under house arrest. While under house arrest, he wrote Two New Sciences, in which he summarized work he had done some forty years earlier on the two sciences now called kinematics and strength of materials.


Heliocentrism 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, 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.It was not until the 16th century that a 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 introduced 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.

History of astronomy

Astronomy is the oldest of the natural sciences, dating back to antiquity, with its origins in the religious, mythological, cosmological, calendrical, and astrological beliefs and practices of prehistory: vestiges of these are still found in astrology, a discipline long interwoven with public and governmental astronomy. It was not completely separated in Europe (see astrology and astronomy) during the Copernican Revolution starting in 1543. In some cultures, astronomical data was used for astrological prognostication.

Ancient astronomers were able to differentiate between stars and planets, as stars remain relatively fixed over the centuries while planets will move an appreciable amount during a comparatively short time.

Indian astronomy

Indian astronomy has a long history stretching from pre-historic to modern times. Some of the earliest roots of Indian astronomy can be dated to the period of Indus Valley Civilization or earlier. Astronomy later developed as a discipline of Vedanga or one of the "auxiliary disciplines" associated with the study of the Vedas, dating 1500 BCE or older. The oldest known text is the Vedanga Jyotisha, dated to 1400–1200 BCE (with the extant form possibly from 700–600 BCE).Greek astronomy was influenced by Indian astronomy and vice versa beginning in the 4th century BCE and through the early centuries of the Common Era, for example by the Yavanajataka and the Romaka Siddhanta, a Sanskrit translation of a Greek text disseminated from the 2nd century.Indian astronomy flowered in the 5th–6th century, with Aryabhata, whose Aryabhatiya represented the pinnacle of astronomical knowledge at the time. Later the Indian astronomy significantly influenced Muslim astronomy, Chinese astronomy, European astronomy, and others. Other astronomers of the classical era who further elaborated on Aryabhata's work include Brahmagupta, Varahamihira and Lalla.

An identifiable native Indian astronomical tradition remained active throughout the medieval period and into the 16th or 17th century, especially within the Kerala school of astronomy and mathematics.

Johannes Praetorius

Johann Richter or Johannes Praetorius (1537 – 27 October 1616) was a Bohemian German mathematician and astronomer.

Nicolaus Reimers

Nicolaus Reimers Baer (2 February 1551 – 16 October 1600), also Reimarus Ursus, Nicolaus Reimers Bär or Nicolaus Reymers Baer, was an astronomer and imperial mathematician to Emperor Rudolf II. Due to his family's background, he was also known as Bär, Latinized to Ursus ("bear").

Reimers was born in Hennstedt and received hardly any education in his youth, herding pigs until the age of 18. Yet, Heinrich Rantzau discovered his talents and employed him from 1574 to 1584 as geometer. Accordingly, Reimers in 1580 published a Latin Grammar and in 1583 his Geodaesia Ranzoviana. Rantzau also arranged a meeting with Tycho Brahe.

From 1585 to 1586 he was employed as a private tutor in Pomerania and from 1586 to 1587, Reimers stayed at the court of William IV, Landgrave of Hesse-Kassel in Kassel, where he met Swiss instrument maker Jost Bürgi (1552–1632). Both were autodidacts and thus had a similar background. As Bürgi did not understand Latin, Reimers translated Copernicus' De Revolutionibus Orbium Coelestium into German for Bürgi. A copy of the translation survived in Graz, it is thus called "Grazer Handschrift".Reimers was a bitter rival of Tycho Brahe (his successor as imperial mathematician) after he tried to claim the Tychonic system as his own. Tycho complained that Ursus had plagiarized both his system of the world, as well as the publication of the mathematical model of prosthaphaeresis. History has sided with Ursus on the later issue, and he had stated that the technique was the invention of Paul Wittich and Jost Bürgi.

In 1588 he claimed to have devised a model of the solar system where the planets revolved around the Sun, while the Earth only spun around on its axis. In this he differed from Copernicus, who had postulated also that the Earth orbited the Sun. Ursus objected to the Copernican model as it violated the Aristotelian principle of not allowing more than one natural movement by a body.

Johannes Kepler committed a faux pas early in his career by sending a laudatory letter to Reimers while seeking the patronage of Tycho. Ursus published the letter in the preface to his work claiming priority for Tycho's cosmological ideas.But unlike Tycho's geoheliocentric system in which the Earth does not rotate and the Martian and Solar orbits intersect, in that of Ursus and his follower Roslin the Earth had a daily rotation and also the Martian and Solar orbits do not intersect, thus avoiding the Tychonic conclusion in respect of the Martian orbit that there are no solid celestial spheres on the ground that they cannot possibly interpenetrate. But on the other hand the orbits of Mercury and Venus would obviously intersect the Martian orbit in Reimers' illustration of his model, and indeed also intersect Jupiter's orbit.

However Kepler discovered Tycho had posited intersecting Martian and Solar orbits because he had mistakenly concluded from his data that at opposition Mars was closer to the Earth than the Sun was. The source of the error was a research assistants' mistaken calculation of Mars's daily parallax from observations during its 1582-3 opposition as greater than that of the Sun's presumed 3' parallax. Kepler discovered Tycho’s observations revealed little or no Martian parallax, implying it was further than the Sun at opposition. This would have refuted Tycho's system in favour of Ursus's and Roslin's. It seems it has yet to be determined whether the dominant astronomical system of the 17th century was the geoheliocentric system of Tycho or that of Ursus and Roslin at least in respect of non-intersecting Solar and Martian orbits, and also in that of the Earth's rotation or not.

Reimers died in Prague.

Nilakantha Somayaji

Kelallur Nilakantha Somayaji (also referred to as Kelallur Comatiri; 14 June 1444 – 1544) was a major mathematician and astronomer of the Kerala school of astronomy and mathematics in India. One of his most influential works was the comprehensive astronomical treatise Tantrasamgraha completed in 1501. He had also composed an elaborate commentary on Aryabhatiya called the Aryabhatiya Bhasya. In this Bhasya, Nilakantha had discussed infinite series expansions of trigonometric functions and problems of algebra and spherical geometry. Grahapareeksakrama is a manual on making observations in astronomy based on instruments of the time. Known popularly as Kelallur Chomaathiri, he is considered an equal to Kottessori Parameshwaran Kundisori.

Outline of astronomy

The following outline is provided as an overview of and topical guide to astronomy:

Astronomy – studies the universe beyond Earth, including its formation and development, and the evolution, physics, chemistry, meteorology, and motion of celestial objects (such as galaxies, planets, etc.) and phenomena that originate outside the atmosphere of Earth (such as the cosmic background radiation).

Phases of Venus

The phases of Venus are the variations of lighting seen on the planet's surface, similar to lunar phases. The first recorded observations of them were telescopic observations by Galileo Galilei in 1610. Although the extreme crescent phase of Venus has been observed with the naked eye, there are no indisputable historical pre-telescopic records of it being observed.

Simon Marius

Simon Marius (Latinized from German Simon Mayr; January 20, 1573 – January 5, 1625) was a German astronomer. He was born in Gunzenhausen, near Nuremberg, but he spent most of his life in the city of Ansbach. He is most noted for making the first observations of the four largest moons of Jupiter, before Galileo himself, and his publication of his discovery led to charges of plagiarism. He is also known for the first European observation of the Andromeda Galaxy.


Tantrasamgraha, or Tantrasangraha, (literally, A Compilation of the System) is an important astronomical treatise written by Nilakantha Somayaji, an astronomer/mathematician belonging to the Kerala school of astronomy and mathematics.

The treatise was completed in 1501 CE. It consists of 432 verses in Sanskrit divided into eight chapters. Tantrasamgraha had spawned a few commentaries: Tantrasamgraha-vyakhya of anonymous authorship and Yuktibhāṣā authored by Jyeshtadeva in about 1550 CE.

Tantrasangraha, together with its commentaries, bring forth the depths of the mathematical accomplishments the Kerala school of astronomy and mathematics, in particular the achievements of the remarkable mathematician of the school Sangamagrama Madhava.

In his Tantrasangraha, Nilakantha revised Aryabhata's model for the planets Mercury and Venus. His equation of the centre for these planets remained the most accurate until the time of Johannes Kepler in the 17th century.It was C.M. Whish, a civil servant of East India Company, who brought to the attention of the western scholarship the existence of Tantrasamgraha through a paper published in 1835. The other books mentioned by C.M. Whish in his paper were Yuktibhāṣā of Jyeshtadeva, Karanapaddhati of Puthumana Somayaji and Sadratnamala of Sankara Varman.

The Assayer

The Assayer (Italian: Il Saggiatore) was a book published in Rome by Galileo Galilei in October 1623 and is generally considered to be one of the pioneering works of the scientific method, first broaching the idea that the book of nature is to be read with mathematical tools rather than those of scholastic philosophy, as generally held at the time.

Timeline of cosmological theories

This timeline of cosmological theories and discoveries is a chronological record of the development of humanity's understanding of the cosmos over the last two-plus millennia. Modern cosmological ideas follow the development of the scientific discipline of physical cosmology.

Tycho Brahe

Tycho Brahe (; born Tyge Ottesen Brahe; 14 December 1546 – 24 October 1601) was a Danish nobleman, astronomer, and writer known for his accurate and comprehensive astronomical and planetary observations. He was born in the then Danish peninsula of Scania. Well known in his lifetime as an astronomer, astrologer and alchemist, he has been described as "the first competent mind in modern astronomy to feel ardently the passion for exact empirical facts." His observations were some five times more accurate than the best available observations at the time.

An heir to several of Denmark's principal noble families, he received a comprehensive education. He took an interest in astronomy and in the creation of more accurate instruments of measurement. 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. His system correctly saw the Moon as orbiting Earth, and the planets as orbiting the Sun, but erroneously considered the Sun to be orbiting the Earth. Furthermore, he was the last of the major naked-eye astronomers, working without telescopes for his observations. In his De nova stella (On the New Star) of 1573, he refuted the Aristotelian belief in an unchanging celestial realm. His precise measurements indicated that "new stars" (stellae novae, now known as supernovae), in particular that of 1572, lacked the parallax expected in sublunar phenomena and were therefore not tailless comets in the atmosphere as previously believed but were above the atmosphere and beyond the moon. Using similar measurements he showed that comets were also not atmospheric phenomena, as previously thought, and must pass through the supposedly immutable celestial spheres.

King Frederick II granted Tycho an estate on the island of Hven and the funding to build 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 Uraniborg were not sufficiently steady. On the island (where he behaved autocratically toward the residents) he founded manufactories, such as a paper mill, to provide material for printing his results. After disagreements with the new Danish king, Christian IV, in 1597, he went into exile, and was invited by the Bohemian king and Holy Roman Emperor Rudolph II to Prague, where he became the official imperial astronomer. He built an observatory at Benátky nad Jizerou. There, from 1600 until his death in 1601, he was assisted by Johannes Kepler, who later used Tycho's astronomical data to develop his three laws of planetary motion.

Tycho's body has been exhumed twice, in 1901 and 2010, to examine the circumstances of his death and to identify the material from which his artificial nose was made. The conclusion was that his death was likely caused by a burst bladder, and not by poisoning as had been suggested, and that the artificial nose was more likely made of brass than silver or gold, as some had believed in his time.

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