In November 11, 1572, a young 26 year old Danish astronomer observes a bright light source in the constellation Cassiopeia. According to the conception of that time, the supralunar region was supposed to be unchanging and perfect. The appearance of a new star was a mystery. This spectacular event greatly impressed the young Tycho Brahe. For two weeks, the star was visible during the day. In December, the light intensity decreased and the color went from white, yellow, orange and light red. He observed the brightness of the star until it vanished in March 1574. He recorded all his observations in a book he called "De Stella Nova". He published it in 1573. This book made him famous throughout Europe.
We now know that Tycho Brahe was not a witness of the birth of a star, but a stellar explosion. This phenomenon is called nova or supernova. The accurate measurements that he made proved that the " Stella Nova "was well beyond the sublunary realm. Tycho Brahe's observations will challenge the two thousand years old Aristotelian conceptions that the celestial sphere is unchanging and perfect. He devoted the rest of his life to astronomy.