Editing Tychonic system (section)

== Motivation for the Tychonic system ==
Tycho admired aspects of Copernicus's [[heliocentrism|heliocentric model]], but felt that it had problems as concerned physics, astronomical observations of stars, and religion. Regarding the Copernican system, Tycho wrote,
<blockquote>
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.<ref>{{cite book |first=Owen |last=Gingerich |title=The eye of heaven: Ptolemy, Copernicus, Kepler |location=New York |publisher=[[American Institute of Physics]] |date=1993 |page=181 |isbn=0-88318-863-5}} Quoting from Tycho Brahe’s ''De Mundi Aetherei'', p. 185</ref>
</blockquote>

(The "triple motion" refers to its daily rotation, yearly revolution, and [[axial precession]].) 

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 (classical element)|"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.<ref>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.</ref> 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 <blockquote>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.<ref>Blair, 1990, 361.</ref> </blockquote>

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]]<ref>J J O'Connor and E F Robertson. [http://www-history.mcs.st-andrews.ac.uk/Biographies/Bessel.html Bessel biography]. [[University of St Andrews]]. Retrieved 2008-09-28</ref>).  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.<ref>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 and Alcor|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 {{cite journal |url=http://www.leosondra.cz/en/mizar/ |first=L. |last=Ondra |title=A New View of Mizar |journal=[[Sky & Telescope]] |date=July 2004 |volume=108 |issue=1 |pages=72–75 |bibcode=2004S&T...108a..72O}}]. 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.</ref> 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 (most stars visible to the naked eye are [[giant star|giants]], [[supergiant]]s, 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.<ref>Blair, 1990, 364. Moesgaard, 1972, 51.</ref> Tycho said<blockquote>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.<ref>Blair, 1990, 364.</ref></blockquote> 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.<ref>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, [[Sophie Roux|S. Roux]], eds.) Firenze: Olski 2007: 121–141, pages 124–125.</ref>  In fact, Rothmann responded to this argument of Tycho's by saying <blockquote>[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?<ref>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.</ref></blockquote>

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.<ref>Blair, 1990, 362–364</ref>

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.<ref>Gingerich, 1973. Moesgaard, 1972, 40–43.</ref> 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.<ref>Moesgaard 40, 44</ref><ref>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/</ref>

=== Precursors to geoheliocentrism ===
Tycho was not the first to propose a geoheliocentric system. It used to be thought that [[Heraclides Ponticus|Heraclides]] in the 4th century BC had suggested that [[Mercury (planet)|Mercury]] and [[Venus]] revolve around the Sun, which in turn (along with the other planets) revolves around the Earth.<ref>{{Cite journal |volume=23 |page=233 |last=Eastwood |first=B. S. |title=Heraclides and Heliocentrism – Texts Diagrams and Interpretations |journal=[[Journal for the History of Astronomy]] |date=1992-11-01 |issue=4 |doi=10.1177/002182869202300401 |bibcode=1992JHA....23..233E |s2cid=118643709}}</ref> [[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]].<ref>{{Cite book |last=Neugebauer |first=Otto E. |title=A history of ancient mathematical astronomy |publisher=Birkhäuser |date=1975 |isbn=3-540-06995-X |author-link=Otto E. Neugebauer}}</ref><ref>{{Cite journal |title=The astronomical system of Copernicus |last=Rufus |first=W. Carl |journal=[[Popular Astronomy (US magazine)|Popular Astronomy]] |volume=31 |pages=510–521 [512] |date=1923 |bibcode=1923PA.....31..510R}}</ref> 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 of astronomy and mathematics|Kerala school]] astronomer [[Nilakantha Somayaji]], whose geoheliocentric system also had all the planets revolving around the Sun.<ref>{{cite journal |last1=Ramasubramanian |first1=K. |last2=Srinivas |first2=M. D. |last3=Sriram |first3=M. S. |date=1994 |title=Modification of the earlier Indian planetary theory by the Kerala astronomers (c. 1500 AD) and the implied heliocentric picture of planetary motion] |journal=[[Current Science]] |volume=66 |pages=784–790|url=http://www.physics.iitm.ac.in/~labs/amp/kerala-astronomy.pdf}}</ref><ref>{{Cite journal |title=Model of planetary motion in the works of Kerala astronomers |year=1998 |last=Ramasubramanian |first=K. |journal=Bulletin of the Astronomical Society of India |volume=26 |pages=11–31 [23–4] |bibcode=1998BASI...26...11R}}</ref>{{sfn|Joseph|2000|p=408}} 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. He was also anticipated by the cosmology depicted in the [[Leiden Aratea]], a Carolingian manuscript created in the early 9th Century for the Carolingian court. <ref>{{Cite book |last=de Hamel |first=Christopher |title=Meetings with Remarkable Manuscripts |publisher=Allen Lane |date=2016 |isbn=978-0-241-00304-6 |author-link=Christopher de Hamel}}</ref>