An heir to several of Denmark's principal noble families, Tycho received a comprehensive education. He took an interest in astronomy and in the creation of more accurate instruments of measurement. As an astronomer, Tycho worked to combine what he saw as the geometrical benefits of the Copernican system with the philosophical benefits of the Ptolemaic system into his own model of the universe, the Tychonic system. His system correctly saw the Moon as orbiting Earth, and the planets as orbiting the Sun, but erroneously considered the Sun to be orbiting the Earth. Furthermore, he was the last of the major naked-eye astronomers, working without telescopes for his observations. In his "De nova stella" ("On the New Star") of 1573, he refuted the Aristotelian belief in an unchanging celestial realm. His precise measurements indicated that "new stars" (stellae novae, now known as supernovae), in particular that of 1572 (SN 1572), lacked the parallax expected in sublunar phenomena and were therefore not tailless comets in the atmosphere as previously believed but were above the atmosphere and beyond the Moon. Using similar measurements, he showed that comets were also not atmospheric phenomena, as previously thought, and must pass through the supposedly immutable celestial spheres.