text: who is tycho brahe?   "...was a danish (scanian) nobleman astronomer as well as an astrologer and alchemist  he is credited with the most accurate astronomical observations of his time, and the data was used by his assistant kepler to derive the laws of planetary motion. no one before tycho had attempted to make so many redundant observations, and the mathematical tools to take advantage of them had not yet been developed. he did what others before him were unable or unwilling to do — to catalogue the planets and stars with enough accuracy so as to determine whether the ptolemaic or copernican system was more valid in describing the heavens."