Tycho Brahe's Revolutionary Astronomical Observations and the New Star Discovery

After the publication of his work on the "new star" followed by a dissemination of his ideas in various university circles, he convinced the Danish king Frederick II to grant him an entire island on which to erect a castle entirely dedicated to stellar observation. From his youth, precisely from the first observations of the 1572 comet, Tycho Brahe had realized that it was possible to gain several orders of magnitude in the precision of observations simply by building instruments of larger than ordinary dimensions. He thus had enormous observation instruments built for Uraniborg which, combined with revolutionary conceptual innovations made by Brahe himself, led to a notable improvement in the precision of observations. Tycho Brahe indeed studied the error of various instruments, formalized for the first time the problems of atmospheric refraction and finally decided to observe the planets not only at certain well-defined moments of their path, but during their entire course in orbit, thus illuminating the irregularities of their trajectory. The variation in planetary velocities and the quantitative data that led Kepler to formulate the hypothesis on orbital eccentricity are owed precisely to the change in approach to observations made by Tycho Brahe at Uraniborg. The Uraniborg project was immense, ambitious and expensive, however its realization, even if only partially implemented by the financing of Rudolf II, constituted the springboard for the subsequent leap in the development of astronomical conceptions of the time. The Rudolfine Tables One of the 12 fundamental criticisms that Pico della Mirandola had directed at divinatory astrology was precisely related to the uncertainty in planetary ephemerides that led, according to Pico della Mirandola, to incoherent results. Tycho Brahe's life, in a certain way, was entirely dedicated to solving this problem related to judicial astrology. At the time, there were indeed two types of astronomical tables: the Prutenic and the Alfonsine. The Prutenic tables were calculated by Reinhold in 1551 taking the Copernican system as the basic theory for his calculations, conversely the Alfonsine tables, dating back to Alfonso X of Castile who commissioned their drafting in 1252, were based on the Ptolemaic system. Tycho Brahe remained dissatisfied with both and generally for important horoscopes, such as those of the royals of the Danish family, combined the two systems using the Alfonsine tables derived from the Ptolemaic system for the outer planets, while the Prutenic ones according to Copernican theory for the inner ones. Already in these horoscopes of the Danish royal family, one can glimpse what would be the idea of the Tychonic system, a middle way between the Copernican and Ptolemaic systems in which the outer planets follow Ptolemaic theory, but the inner ones and in particular Mercury follow Copernican theory. To these two systems anyway, Tycho Brahe always added his own personal observations, a sign of his dissatisfaction with both these systems. Tycho Brahe died without seeing the compilation of the tables he worked on his entire life completed, and which were finished by his apprentice, Kepler, who about twenty years later managed to solve the age-old problem of Mars's motion. In 1627, the Rudolfine tables were thus published, based on Tycho Brahe's observations and Kepler's calculations, and they constituted the basis for a new foundation of astronomy. III If on one hand astrology's attention shifts toward an interior character dimension and every practical and judicial application is hindered, astronomy on the other hand finds itself having to lose essentially its main reason for existing and therefore having to reinvent itself. In this context, the action of two extremely important astronomer-astrologers in the history of science was important: Tycho Brahe and Johannes Kepler. The New Star On a splendid November evening in 1572, Tycho Brahe, leaving his uncle's alchemical laboratory, caught sight of a star in the sky that was not only brighter than all other celestial objects present after the Moon and Venus, but which moreover corresponded to nothing that had ever been observed before. The star in question was, in all respects, a new star. The idea of a new star clashed with much of the knowledge that was considered consolidated at the time. The Aristotelian system indeed presupposed an immutable sky and to this vision was joined that of theologians who postulated the cessation of the divine creative act that occurred on the seventh day of Genesis. Tycho Brahe remained so surprised and fascinated by the phenomenon that he decided to interrupt his alchemical studies to dedicate himself almost entirely to astronomical studies, which had constituted an old, albeit forbidden passion. After more than eighteen months of continuous observations of the celestial phenomenon through an instrument he himself built, Tycho Brahe managed to determine the total absence of a parallax angle between the nova star and the constellation of Cassiopeia. The lack of any parallax angle positioned the celestial phenomenon very far from Earth and certainly beyond the sky of the Moon before which the inflammation of the exhalation that constituted the Aristotelian explanation of the phenomenon should have occurred. According to Aristotle indeed, celestial phenomena of this type had to be ascribed to dry terrestrial exhalations that reached the sphere of fire, igniting. The total absence of movement over time relative to the stellar background excluded, at least in this case, the Aristotelian explanation. In 1573 Tycho Brahe proceeded to draft his De Nova Stella, presenting his results to the scientific community. It is difficult to correctly estimate the importance of this writing and the impact that this type of celestial phenomena had on the scientific community. Although Tycho Brahe does not draw in his De Nova Stella the conclusions of his observations that would invalidate the Ptolemaic system, nevertheless for the first time astronomical observation is used as a critical instrument capable of experimentally confirming or invalidating doctrines or metaphysical conceptions. Although similar phenomena had already occurred in the past indeed, no one had attributed to them a value capable of substantially invalidating or denying Aristotelian theory. In practice, astronomical observation as an experimental instrument for...