ASTRONOMY (Greek ’αστρον [astron]—star, light; νομος [nomos]—law, priniple)—the oldest mathematical-physical science, the object of which are the heavenly bodies and the matter distributed throughout the universe.
In the historical development of astrology in connection with the successive expansion of its scope and research methods (teledetection, telescopes) divisions of astronomy arose such as astrometrics (spherical astrometrics and nautical astrometrics), celestial mechanics, astrophysics, radioastronomy, astronautics, geodesic astronomy, and extragalactic astronomy. Megalithic monuments such as Carnac and Stonehenge show that an astronomical science existed even at the end of the Neolithic era (4,000 BC). This knowledge as developed in the civilizations of ancient Egypt, Mesopotamia, and elsewhere. In those civilizations the first systematic astronomical observations were made, but only the Greeks in sixth century BC were able to move from empirical astronomy to theoretical astronomy. Yet even in the fifth century BC, Greek astronomy, like that of the near east, was dominated by the study of meteorological phenomena such as clouds, wind, lightning, and rainbows.
In that period Parmenides of Elea discovered the spherical shape of the Earth, Empedocles and Anaxagoras explained solar eclipses by laws (although their explanation was only partial), and Democritus made a catalogue of the stars. There was noticeable progress in the fourth century BC when a quantitative model of the motion of celestial bodies appears called the system of homocentric spheres by Eudoxos. This model was further developed by Eudoxos’ student Polemarchos. Callipos, a student of Polemarchos, made important changes in the model of the homocentric spheres and added new spheres to the model. Aristotle relied on the conception of Eudoxos and presented his astronomical theory in a metaphysical and theological context. Aristotle introduced the conception of the first unmoved mover (το πρωτον κινουν ’ακινυητον [to proton kinoun akineton], Phys., 256 a 9), and thereby gave it final sanction in Greek science.
In the subsequent development of astronomy (or astrometrics) the consistent application of the language of mathematics (Euclidean geometry) was most essential. This was the result of strong links between this field of knowledge and Pythagoreanism. In Pythagoreanism there had always been a dominant methodological orientation that tended to treat the process of knowledge in mathematical terms. Plato followed the Pythagoreans when he accepted the doctrine that the heavenly bodies move in circular motions. In connection with this, the astronomers of Plato’s time asked whether these motions were circular, uniform, and perfectly regular, which had to be presupposed hypothetically in order to save the phenomena of the planets. In this period we may see a significant growth in the mathematical methods the would find application in astronomy. In the late fourth and early third century BC, Euclid’s Elements, Autolichos of Pitana’s treatise on spherical geometry, and other such works were published. The theoretical conceptions of Apollonius (epicycles, eccentrics) and Hipparchus’ discoveries (the astrolabe, elliptical coordinates, precession, a method for calculating the length of the tropical year) were also important contributions to mathematical astronomy. New methods and theoretical conceptions not only contributed to the development of astronomy, but also inspired discussion on the object and functions of astronomy.
According to Ptolemy’s Μαθηματικη συνταξις [Mathematike syntaxis], the object of astronomy, understood as a mathematical science, is not empirical beings, but mathematical entities (i.e., such as can be constructed in astronomical hypotheses), ideal being, i.e., deferents, eccentrics, and epicycles. The function of astronomy is (assuming the existence of such beings) to explain the configuration and motion of celestial bodies in their relations to each other and to the earth, that is, astronomy should formulate hypotheses that would be in agreement with observed phenomena. In connection with Ptolemy’s methodological conceptions, or more precisely, in connection with the consequences these conceptions had for observational astronomy, an instrumental conception of the cognitive status of astronomical theory appeared relatively early. This conception was expressed in abbreviation in the form of a methodological directive: σωζτειν τα φαινομενα [sozein ta phainomena] (saving appearances). The fact that the same phenomena can be reconstructed and explained with the help of various hypotheses became the starting point when asking about the criteria by which one of several possible hypotheses concerning the same domain of phenomena would be chosen. In ancient times the Peripatetics had already taken a realistic approach to this problem (Adrastos of Aphrodisia, Theon of Smyrna). They thought that when astronomer is faced with the choice of hypotheses he should be guided by the criterium of the agreement of the hypothesis with physical theory, since physical theory explains the nature of things. Besides the realistic approach, there was also the approach of the Skeptics (Sextus Empiricus) who thought that disputes concerning the superiority of one astronomical hypothesis over another, when both provide a satisfactory explanation of the same phenomenon, are futile. The most famous astronomer of ancient times, Ptolemy, proposed a third answer—in his conventionalist and rationalist approach, the science that reveals the essence of things and may serve as the criterion for a choice between hypotheses is not physics (the philosophy of nature) but mathematics. More precisely, the mathematical simplicity of astronomical hypotheses is the best criterion.
The criterium of mathematical simplicity as the criterium for a choice between competing astronomical theories continued to modern times. Descartes, among others, used this criterium in his Principia philosophiae at the time of the seventeenth century methodological discussion on the then-competing astronomic hypotheses of Copernicus and Tycho Brahe. The instrumentalist conception of the cognitive status of an astronomical hypothesis that may be found in Ptolemy’s Μαθηματικη συνταξις survived past the decline of the ancient world and was taken up by the scholastics. We may find it in the classic texts of that period. For example, in St. Thomas Aquinas (S. th., I q. 32, a. 1) we find a distinction between a hypothesis that must be true, and a hypothesis that is merely in agreement with the facts. Metaphysical (or physical) hypotheses belong to the first group, and astronomical (mathematical) hypotheses belong to the second group. Copernicus was the first to depart from this position. He held that an astronomical (mathematical) hypothesis, just like a metaphysical hypothesis, may also be true by necessity. Copernicus, however, was unable to follow through in the realization of this methodological postulate.
When scientists consistently followed Copernicus’ position, this led to the modern conception of astronomy (physical astronomy) and in a further perspective it led to the conception of modern science (mathematical natural science). This aspect of Copernicus’ thought from the perspective of the genesis of modern mathematical natural science seems even more important that the strictly astronomical elements of Copernicanism. The most important achievements of Copernicus’ heliocentric astronomy could be reconstructed within the paradigm of geocentrism, as we can see from the compromise which was Tycho de Brahe’s system (a combination of elements of heliocentrism and geocentrism). Otherwise, the heliocentric idea (the heliostatic idea) also entailed the danger of conflict with a post-Tridentine theology that had a fundamentalist orientation. In a short time this led to the case of Galileo which became very significant in the definition of the relations between science and the Church over the next three centuries.
Astronomical theory from the beginning of the seventeenth century owed the most to the works of Kepler. In his work from the year 1909, Astronomia nova aitiologetos, sue physica coelestis tradita commentariis de motibus stella Martis ex observationibus G. V. Tychonis Brahe, he broke from the tradition of kinematic astronomy (which in its description of the motion of heavenly bodies limited itself to kinetic quantities: velocity and position). Kepler postulated the discovery of real (physical and dynamic) causes for planetary motions hidden in the “God’s pandects”. With this he made the first step toward a new physical astronomic (celestial mechanics).
Newton developed the foundations of celestial mechanics in his fundamental work Principia mathematica philosophiae naturalis, but the further development of celestial mechanics was the work of scholars of the French school (J. L. Lagrange, A. M. Legendre, P. S. Laplace). Laplace’s works in particular (Exposition du système du monde, P 1796; Traité de mécanique céleste, I–V, P 1799–1825) were important not only for celestial mechanics but for philosophical interpretations of the new astronomy (mechanicism). Besides many discussions of particular matters in the works, in them for the first time appeared mathematically justified hypotheses that were philosophically and cosmologically important (including the Kant-Laplace hypothesis that the solar system came from a primal fog, and the stability hypothesis, i.e., that the orbits of all the bodies of the solar system have practically unchanging orbits). The most important general conclusion turned out to be the refutation of Newton’s conclusion that the intervention of supernatural powers was required to maintain the stability of the solar system. This led to the firm establishment of the idea of mechanicism and in a further perspective to scientism. The successes of Newtonian mechanics also had a certain significance in this process expressed in the discovery of new planets in the solar system (Uranus, Neptune, and Pluto), and in the application of new methods in physics (spectral analysis) which led to astrophysics. In astrophysics scientists refuted, among other things, A. Comte’s well-known prediction that humanity would never know the chemical composition of celestial bodies.
In the twentieth century beginning in the 1930s, but in fact by the end of the 1950s, radioastronomy appeared. Its observation techniques allowed scientists to detect objects emitting electromagnetic radiation outside the visible spectrum. With the new observation techniques they discovered new objects: pulsars and quasars. The most spectacular scientific event turned out to be the discovery (A. Penzias, R. W. Wilson) of background radiation that matched the radiation of a perfectly black body at a temperature of 3.5 degrees Kelvin, which was interpreted as a proof of the big bang theory. With the development of rockets and satellites there were more possibilities for astronomical observation. This led to new types of research (geodesic astronomy, extragalactic astronomy) that are making it possible not only to learn more about the distant regions of the cosmos but also about Earth itself.
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Zenon E. Roskal