of fixed stars'
Background image: The remnant of supernova SN 1572, as it appears in the X-ray spectrum, 8-10,000 light years away, in the constellation of Cassiopeia.
Modern cosmology in a broad sense started in 1572, with the observation, by Tycho Brahe and many others, of a new star that appeared in the constellation of Cassiopeia, between 2nd and 8th November, that for a brief period matched Venus in brightness. The following year Tycho Brahe published the first edition of his De nova et nullius aevi memoria prius visa stella ("Concerning the Star, new and never before seen in the life or memory of anyone"). The new star was a supernova (SN 1572), one of only 8 that had been documented up to that time. But unlike the others, this one promoted extensive debates and brought about the widespread perception that new and more precise star catalogues should be made, in turn requiring new and better astronomical instruments. In this way the observation of SN 1572, often called ‘Tycho’s supernova’, brought about a transformation in astronomy and a decisive turning away from the sharp separation, made by Aristotle among others, between an unchanging realm of fixed stars and the realm of mundane phenomena. It paved the way not only for Kepler’s improved observations of the planets and the discovery of Kepler’s laws, but also for Newton’s subsequent unification of terrestrial and celestial gravitational phenomena.
Tycho’s supernova remained visible to the naked eye for almost two years, but it was not subsequently observed until its detection, almost four centuries later, by R. Hanbury-Brown and C. Hazard at Jodrell Bank as a radio source at 158.5 MHz. It was first detected again as an optical source in the 1960s using the Mount Palomar telescope.