Editing Johannes Kepler (section)

=== Reception of his astronomy ===
[[Kepler's laws of planetary motion]] were not immediately accepted. Several major figures such as [[Galileo]] and [[René Descartes]] completely ignored Kepler's ''Astronomia nova''. Many astronomers, including Kepler's teacher, Michael Maestlin, objected to Kepler's introduction of physics into his astronomy. Some adopted compromise positions. [[Ismaël Bullialdus]] accepted elliptical orbits but replaced Kepler's area law with uniform motion in respect to the empty focus of the ellipse, while [[Seth Ward (bishop)|Seth Ward]] used an elliptical orbit with motions defined by an equant.<ref>For a detailed study of the reception of Kepler's astronomy see Wilbur Applebaum, [http://adsabs.harvard.edu/abs/1996HisSc..34..451A "Keplerian Astronomy after Kepler: Researches and Problems"], ''History of Science'', 34(1996): 451–504.</ref><ref>Koyré, ''The Astronomical Revolution'', pp.&nbsp;362–364</ref><ref>North, ''History of Astronomy and Cosmology'', pp.&nbsp; 355–360</ref>

Several astronomers tested Kepler's theory, and its various modifications, against astronomical observations. Two transits of Venus and Mercury across the face of the sun provided sensitive tests of the theory, under circumstances when these planets could not normally be observed. In the case of the transit of Mercury in 1631, Kepler had been extremely uncertain of the parameters for Mercury, and advised observers to look for the transit the day before and after the predicted date. [[Pierre Gassendi]] observed the transit on the date predicted, a confirmation of Kepler's prediction.<ref>{{cite journal |first=Albert |last = van Helden |title = The Importance of the Transit of Mercury of 1631 |journal=Journal for the History of Astronomy |volume=7 |year=1976 |pages=1–10 |bibcode = 1976JHA.....7....1V |doi=10.1177/002182867600700101 |s2cid = 220916972 }}</ref> This was the first observation of a transit of Mercury. However, his attempt to observe the [[transit of Venus]] just one month later was unsuccessful due to inaccuracies in the Rudolphine Tables. Gassendi did not realize that it was not visible from most of Europe, including Paris.<ref>{{cite web |author=HM Nautical Almanac Office |url=http://www.nao.rl.ac.uk/nao/transit/V_1631/ |title=1631 Transit of Venus |date=10 June 2004 |access-date=28 August 2006 |archive-url=https://web.archive.org/web/20061001062918/http://www.nao.rl.ac.uk/nao/transit/V_1631/ |archive-date=1 October 2006 |url-status=dead}}</ref> [[Jeremiah Horrocks]], who observed the [[Transit of Venus, 1639|1639 Venus transit]], had used his own observations to adjust the parameters of the Keplerian model, predicted the transit, and then built apparatus to observe the transit. He remained a firm advocate of the Keplerian model.<ref>Allan Chapman, [http://adsabs.harvard.edu/abs/1990QJRAS..31..333C "Jeremiah Horrocks, the transit of Venus, and the 'New Astronomy' in early 17th-century England"], ''Quarterly Journal of the Royal Astronomical Society,'' 31 (1990): 333–357.</ref><ref>North, ''History of Astronomy and Cosmology'', pp.&nbsp; 348–349</ref><ref>Wilbur Applebaum and Robert Hatch, [http://adsabs.harvard.edu/abs/1983JHA....14..166A "Boulliau, Mercator, and Horrock's ''Venus in sole visa'': Three Unpublished Letters"], ''[[Journal for the History of Astronomy]]'', 14(1983): 166–179</ref>

''Epitome of Copernican Astronomy'' was read by astronomers throughout Europe, and following Kepler's death, it was the main vehicle for spreading Kepler's ideas. In the period 1630–1650, this book was the most widely used astronomy textbook, winning many converts to ellipse-based astronomy.<ref name="Gingerich pp 302" /> However, few adopted his ideas on the physical basis for celestial motions. In the late 17th century, a number of physical astronomy theories drawing from Kepler's work—notably those of [[Giovanni Alfonso Borelli]] and [[Robert Hooke]]—began to incorporate attractive forces (though not the quasi-spiritual motive species postulated by Kepler) and the Cartesian concept of [[Principle of inertia (physics)|inertia]].<ref>Lawrence Nolan (ed.), ''The Cambridge Descartes Lexicon'', Cambridge University Press, 2016, "Inertia."</ref> This culminated in Isaac Newton's ''[[Philosophiae Naturalis Principia Mathematica|Principia Mathematica]]'' (1687), in which Newton derived Kepler's laws of planetary motion from a force-based theory of [[Newton's law of universal gravitation|universal gravitation]],<ref>Kuhn, ''The Copernican Revolution'', pp.&nbsp;238, 246–252</ref> a mathematical challenge later known as "solving the [[Kepler problem]]".<ref name=":02">{{Cite book |last1=Frautschi |first1=Steven C. |title=The Mechanical Universe: Mechanics and Heat |title-link=The Mechanical Universe |last2=Olenick |first2=Richard P. |last3=Apostol |first3=Tom M. |last4=Goodstein |first4=David L. |date=2007 |publisher=Cambridge University Press |isbn=978-0-521-71590-4 |edition=Advanced |location=Cambridge [Cambridgeshire] |pages=451 |oclc=227002144 |author-link=Steven Frautschi |author-link3=Tom M. Apostol |author-link4=David L. Goodstein}}</ref>