Editing Tycho Brahe (section)

====1572 supernova====
[[File:Brahe-6.jpg|alt=Title page to De nova stella, in a facsimile reprint of the original 1573 edition (1901)|thumb|The title page to ''De nova stella'', in a facsimile reprint of the original 1573 edition, 1901]]
On 11 November 1572, Tycho observed, from Herrevad Abbey,  a very bright star, now numbered [[SN 1572]], which had unexpectedly appeared in the constellation [[Cassiopeia (constellation)|Cassiopeia]]. Because it had been maintained since [[Ancient history|antiquity]] that the world beyond the Moon's orbit was eternally unchangeable, with celestial immutability being a fundamental axiom of the [[Aristotelianism|Aristotelian]] world-view, other observers held that the phenomenon was something in the terrestrial sphere below the Moon. However, Tycho observed that the object showed no daily [[Diurnal parallax|parallax]] against the background of the fixed stars. This implied that it was at least farther away than the Moon and those planets that do show such parallax. He found that the object did not change its position relative to the fixed stars over several months, as all planets did in their periodic orbital motions, even the outer planets, for which no daily parallax was detectable.{{sfn|Christianson|2000|pages=17–18}}{{sfn|Thoren|Christianson|1990|pp=55–60}}

This suggested that it was not even a planet, but a fixed star in the stellar sphere beyond all the planets. In 1573, he published a small book {{lang|la|De nova stella}},<ref>[http://www.texts.dnlb.dk/DeNovaStella/Index.html ''De nova et nullius ævi memoria prius visa stella'']. {{webarchive|url=https://web.archive.org/web/20090224211014/http://www.texts.dnlb.dk/DeNovaStella/Index.html |date=24 February 2009 }} – Photocopy of the Latin print with a partial translation into Danish: {{lang|da|"Om den nye og aldrig siden Verdens begyndelse i nogen tidsalders erindring før observerede stjerne&nbsp;..."}}</ref><ref>{{Cite book |last=Brahe |first=Tycho |url=https://books.google.com/books?id=X71OAQAAMAAJ&dq=De+nova+stella&pg=PR7 |title=De nova stella: summi civis memor denuo |date=1901 |language=la}}</ref> coining the term [[nova]] for a "new" star. This star was a [[supernova]] and is 7,500&nbsp;[[light-year]]s from Earth. This discovery was decisive for his choice of astronomy as a profession. Tycho was strongly critical of those who dismissed the implications of the astronomical appearance, writing in the preface to {{lang|la|De nova stella}}: {{lang|la|"O crassa ingenia. O caecos coeli spectatores"}} ("O thick wits. O blind watchers of the sky"). The publication of his discovery made him a well-known name among scientists in Europe.{{sfn|Christianson|2000|pages=17–18}}{{sfn|Thoren|Christianson|1990|pp=55–60}}