 Tycho and others had observed the supernova of 1572 . Ottavio Brenzoni 's letter of 15 January 1605 to Galileo brought the 1572 supernova and the less bright nova of 1601 to Galileo 's notice . Galileo observed and discussed Kepler 's supernova in 1604 . Since these new stars displayed no detectable diurnal parallax , Galileo concluded that they were distant stars , and therefore disproved the Aristotelian belief in the immutability of the heavens . 
