Greek Astronomy: Ptolemys Geocentric Model - Assignment Example

Greek Astronomy: Ptolemy’s Geocentric Model Astronomy is a science that deals with the origin, evolution, composition, distance, and motion of heavenly bodies. It originated during the earliest civilization. The Babylonians contributed greatly to the earliest developments in astronomy. With the advent of the Greek astronomers, important cosmological concepts made their way into the ideas regarding the universe (Astronomy, 2006). Some of the important ideas introduced by the Greeks were in respect of the relation between the Earth and the rest of the universe. In the 2nd century AD, the Greek astronomer Ptolemy established the Geo-centric theory, which stated that the Earth was the centre of the universe. This theory was predominant for over fifteen hundred years (Astronomy). Ptolemy’s Geocentric model. Retrieved 16 April 2010 from http://media-2.web.britannica.com/eb-media/84/70084-004-6D5F5F6F.jpg In the 16th century, Nicolaus Copernicus introduced the heliocentric model of the universe, which conjectured that the Sun was at the centre of the universe. Modern astronomy developed with this model, and this era witnessed several discoveries by prominent astronomers, like Johannes Keppler, Galileo, and Isaac Newton. Johannes Kepler discovered the principles of planetary motion; Galileo invented the telescope for observing the universe; and Isaac Newton propounded the laws of motion and gravitation (Astronomy, 2006). Copernican Heliocentric Model. Retrieved 16 April 2010 from http://library.thinkquest.org/28327/main/exploration/people/copernicus.html All these contributions helped in the development of modern astronomy. The invention of spectroscopy and photography in the early 19th century, served to further extend knowledge about planets and other celestial bodies. These inventions provided information about the physical properties of celestial objects; and a new branch of astronomy, namely astrophysics, came into being (Astronomy). In the 2nd century B.C., the Greek astronomer Hipparchus developed mathematical astronomy, which improved its accuracy, considerably. Ptolemy further developed it and made it a complete science. His works were translated, subsequently, by George Trebizond. Thereafter, Johannes Regiomontanus, a German astronomer summarized the works of Ptolemy; which was followed by the majority of the subsequent astronomers. In fifteenth – century Italy, Copernicus was a luminary in astronomy. He made several important contributions to modern astronomy (Greek Astronomy). The ancient Greek astronomers had played a significant role in the development of modern astronomy. The Greek civilization commenced in 600 BC, and the succeeding period was characterized by the development of science in the West. The famous Greek mathematician and astronomer, Pythagoras of Samos, had propounded that the universe was based on the notion of quantification (Lankford 425). All objects, principles or ideas are subject to this concept. This doctrine provided the basis for astronomy, in those days. The followers of Pythagoras theorized that the planets and stars move around the Earth, which was the center of the universe. The planets were assumed to be attached to a crystalline sphere that revolved around the Earth. Pythagoras discovered that the planet Venus was both the morning, as well as the evening star (Lankford 425). Another famous Greek astronomer was Aristotle, who made a several contributions to astronomy. He discovered that the phases of the Moon occur on account of different sunlit portions of the Moon, being visible from the Earth, during the month. He also established that the distance between the Earth and the Sun was greater than the distance between the Earth and the Moon. He discovered that the Moon obstructs the light of the Sun, during solar eclipses, and prevents it from reaching the Earth (Universe). Pythagoras made several discoveries that significantly advanced the science of astronomy. He was the first to discover that the Earth was spherical, in shape. He recognized that the Moon’s orbit was inclined to the equator of the Earth. Pythagoras was interested in mathematical perfection, and believed that even the most complex phenomena must reduce to simple phenomena. This was a path breaking concept that brought about revolutionary changes in the sciences. Great scientists like Newton and Einstein had adopted this approach (O'Connor and Robertson). The Greek mathematician, Oenopides, discovered that the angle contained by the equator and the ecliptic was 240. This discovery was made around 450 BC. Eratosthenes, around 250 BC, confirmed this discovery with minor corrections. Oenopides had recommended a 59 year calendar with 730 months. Eudoxus was a Greek astronomer and mathematician, who perpetuated the ideology of Pythagoras. He was an outstanding astronomer, and his contributions resulted in a new phase in Greek astronomy. Eudoxus proposed models for the motion of celestial bodies and predicted that these bodies underwent circular motion (O'Connor and Robertson). Eudoxus constructed an observatory in Cnidus, and made observations on the Canopus star. This star has an important place in the early history of astronomy. In those days, it was assumed that this star rises and sets in Cnidus. The observatory in Cnidus provided considerable knowledge regarding the rising and setting of constellations and nebulas. Another important astronomical observatory was located in Heliopolis (O'Connor & Robertson). Astronomers of that period made their observations from these two observatories. Eudoxus established a mathematical theory of concentric spheres, by which he attempted to describe and predict the motions of celestial objects. Like Pythagoras, Eudoxus relied on the mathematical interpretation of celestial objects, and never viewed them as physical objects (O'Connor and Robertson). Hipparchus was the most important Greek astronomer of ancient times. Some of his astronomical works are his commentary on Aratus’ astronomical poem, an astronomical calendar, books on arithmetic and optics and works on astrology and geography. The extant information regarding Hipparchus is chiefly derived from the works of Ptolemy. The latter utilized Hipparchus’ findings in his various works (University of Cambridge, Department of History and Philosophy of Science, 1999). Hipparchus made a number of significant contributions that have withstood the test of time. These were not only in the theoretical, but also the practical realm. He understood and employed several geometrical models, such as the eccentric and the deferent – epicycle. He included the numerical data, obtained from observations, into the geometrical models that described the motion of the celestial objects (University of Cambridge, Department of History and Philosophy of Science, 1999). He was a capable and assiduous astronomical observer, and his efforts in this field extended over decades. Some scholars have deemed him to be the founder of trigonometry. Hipparchus employed the dioptra, a measuring device and he is considered to be the inventor of the planispheric astrolabe. The first catalogue of the stars is attributed to him, and his observation of stellar positions is extensive (University of Cambridge, Department of History and Philosophy of Science, 1999). An image of Hipparchus from the title page of William Cunningham's Cosmographicall Glasse (1559) His astronomical studies were truly prolific; and he forayed into such diverse areas of astronomy as the length of the year, the distance between the Earth and the Moon, and the determination of the eclipses of the Sun and the Moon. He propounded theories, regarding the motion of the Sun and the Moon, which he conjectured to be based on uniform circular motion. His greatest achievement was the discovery of the precession of the equinoxes (University of Cambridge, Department of History and Philosophy of Science, 1999). Hipparchus recorded the position of approximately 850 stars, with considerable accuracy. He determined that the Earth’s axis shifted, by 46 seconds of arc every year, with respect of the stellar background. This is a remarkable measurement, as the present day value of this shift is 50.26 seconds of arc. This constitutes the precession of the Earth (Neugebauer, 1975, pp. 240 – 246). Precession of the Equinoxes. Retrieved 16 April 2010, from http://www.redicecreations.com/news/2005/02feb/precession.gif Conclusion The work of Greek astronomers and philosophers, in the area of astronomy was not based on the actual observations of celestial bodies or the cosmos. Their contribution was made on the basis of logical reasoning and mathematical interpretations. They were able to discover that the Earth moves around the Sun, by means of geometrical applications. Furthermore, Greek astronomers were able to calculate the size of the Earth, with considerable precision. Anaxagoras, an astronomer, had propounded some theories that described the manner in which eclipses occurred. Another Greek astronomer, Aristarchus, had propounded that the Earth revolves around the Sun; and Thales had established that the Earth was spherical in shape (Carr). Moreover, they established that the Moon revolves around the Earth. As such, the ancient Greek astronomers had revolutionized our understanding of the cosmos. Works Cited Astronomy. (2006). Retrieved April 15, 2010, from http://www.credoreference.com/entry/ebconcise/astronomy/1 Carr, K. (2009, January 15). Greek Astronomy. Retrieved April 15, 2010, from http://www.historyforkids.org/learn/greeks/science/astronomy/ Greek Astronomy. (n.d.). Retrieved April 15, 2010, from http://www.loc.gov/exhibits/vatican/math.html#ga Lankford, J. (1996). History of astronomy: an encyclopedia. Routledge. Neugebauer, O. (1975). A history of ancient mathematical astronomy. Birkhäuser. O'Connor, J. J., & Robertson, E. F. (n.d.). Greek astronomy. Retrieved April 15, 2010, from http://www.gap-system.org/~history/HistTopics/Greek_astronomy.html universe. (2009, October 10). Retrieved April 16, 2010, from Encyclopædia Britannica Online: http://www.britannica.com/EBchecked/topic/139365/universe/27541/The-system-of-Aristotle-and-its-impact-on-medieval-thought University of Cambridge, Department of History and Philosophy of Science. (1999). Hipparchus . Retrieved April 15, 2010, from http://www.hps.cam.ac.uk/starry/hipparchus.html Read More