He established himself as Europe's leading astronomer with his detailed observations of the new star of 1572. Under the patronage of the king of Denmark, Brahe built the most sophisticated observatory of his day. When the king died, he acquired a new patron in the Holy Roman Emperor, Rudolph II, and built a new observatory in Prague. He pledged to create new and improved tables of planetary motions, dubbed the Rudolphine Tables. For twenty years, he complied much more complete and accurate data than ever before. However, his limited understanding of mathematics and his sudden death in 1601 prevented him from making much sense out of his mass of data. He believed that all the planets except the earth revolved around the sun and that the entire group of sun and planets revolved in turn around the earth-moon system.