Editing Tychonic system (section)

{{Short description|Model of the Solar System proposed in 1588 by Tycho Brahe}}
[[File:Tychonian.png|thumb|A 17th century illustration of the ''Hypothesis Tychonica'' from Hevelius' Selenographia, 1647 page 163, whereby the Sun, Moon, and [[celestial sphere|sphere]] of stars orbit the Earth, while the five known planets (Mercury, Venus, Mars, Jupiter, and Saturn) orbit the Sun.]]
<!-- A reference to the source of this image is needed. -->
[[File:Tychonian system.svg|thumb|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 [[fixed stars|stars]], which rotates.]]

The '''Tychonic system''' (or '''Tychonian system''') is a model of the [[universe]] published by [[Tycho Brahe]] in 1588,<ref name="retrying" /> which combines what he saw as the mathematical benefits of the [[Copernican heliocentrism|Copernican system]] with the philosophical and "physical" benefits of the [[Ptolemaic system]]. The model may have been inspired by [[Valentin Naboth]]<ref>{{cite book |last=Westman |first=Robert S. |author-link=Patronage in Astronomy#Robert Westman |title=The Copernican achievement |url=https://books.google.com/books?id=sLb6k-62vbQC&pg=PA322 |date=1975 |publisher=[[University of California Press]] |isbn=978-0-520-02877-7 |oclc=164221945 |page=322 |via=[[Google Books]]}}</ref> and [[Paul Wittich]], a [[Silesia]]n mathematician and astronomer.<ref>Owen Gingerich, ''The Book Nobody Read: Chasing the Revolutions of Nicolaus Copernicus'', Penguin, {{ISBN|0-14-303476-6}}</ref> A similar cosmological model was independently proposed in the Hindu astronomical treatise ''[[Tantrasamgraha]]'' ({{Circa|1500 CE}}) by [[Nilakantha Somayaji]] of the [[Kerala school of astronomy and mathematics]].<ref>{{Cite book |last=Ramasubramanian |first=K. |title=Tantrasaṅgraha of Nīlakaṇṭha Somayājī |last2=Sriram |first2=M. S. |last3=Somayajī |first3=Nīlakaṇṭha |date=2011 |publisher=Springer |isbn=978-0-85729-035-9 |series=Sources and studies in the history of mathematics and physical sciences |location=Dordrecht |pages=521}}</ref>

It is conceptually a [[geocentric model]], or more precisely geoheliocentric: the [[Earth]] is at the centre of the universe, the [[Sun]] and [[Moon]] and the stars revolve around the Earth, and the other five [[planet]]s revolve around the Sun. At the same time, the motions of the planets are mathematically equivalent to the motions in Copernicus' [[heliocentrism|heliocentric]] system under a simple [[coordinate transformation]], so that, as long as no [[Newton's law of universal gravitation|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.<ref>"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).</ref>