The Hellenic Astronomers - Essay Example

of the of the of the The Hellenic Astronomers Introduction Astronomy consists of the study the universe’s celestial objects; such as stars, planets, comets, galaxies or star systems, and meteors. A number of benefits are derived from astronomy, including an understanding regarding the stars, day and night, phases of the Moon and the seasons. Astronomy has evolved from the study of the movements of the Sun and Moon, into complex theories regarding the origin and composition of the cosmos (History of Astronomy). Figure 1. People have looked up at objects in the sky with fascination since ancient times. That fascination gave birth to the science of astronomy. SOURCE: http://encarta.msn.com/media_701750695_761572208_-1_1/Astronomy.html retrieved on 10 October 2009. Greek Astronomy The indefatigable labors of the ancient Greek astronomers comprise the basis of much of modern astronomy. The scientific history of the West commenced around 600 BC, which coincided with the beginning of the Greek civilization (Lankford 425). Some of the eminent Greek astronomers are described in the sequel. Pythagoras of Samos, Ionia taught that any object, principle or idea in the universe was subject to quantification. This fundamental principle provided a concrete mathematical foundation for the fledgling science of astronomy. The Pythagoreans subscribed to the view that each of the planets was attached to a crystalline sphere that had the Earth as its centre. Pythagoras was the first to discover that the morning star and the evening star were the planet Venus (Lankford 425). Thereafter, Aristotle made a number of astronomical discoveries. For instance, he established that phases of the Moon were on account of different sunlit portions being visible in a month. It was his well founded contention that the Sun was a much greater distance than the Moon, from the Earth; because during a solar eclipse the Sun’s light was prevented from reaching the Earth by the intervening Moon (universe). The shadow of the Earth, which is seen on the Moon, during a lunar eclipse, led Aristotle to conclude that the Earth was spherical in shape. At such times, the Earth is interposed between the Sun and the Moon. On the other hand if the Earth had been a flat disk, then its shadow at the edge would have resembled a straight line. Another piece of evidence that he quoted in support of this theory was that after travelling a great distance south, sojourners were unable to see some of the stars that had been visible from Greece. On a flat earth, any person, irrespective of location would have seen the same stars. However, on a spherical Earth, the view from different latitudes, entails different angles; therefore, the stellar constellations viewed are different (universe). Figure 2. Source: http://www.pas.rochester.edu/~blackman/ast104/aristotle.gif retrieved on 10 October 2009. The astronomers had established that the Earth was a sphere – an oblate spheroid if one desires precision. The nature of eclipses had been determined and then the question arose as to how large was the Earth. This enigmatic issue was resolved by the Greek astronomer Eratosthenes in 200 BC. He observed that on a specific day in Syene (modern day Aswan), Egypt, the Sun at noon was directly overhead. At the same time and on the same day the Sun was 70 south of the zenith at Alexandria, Egypt. Knowing the distance between Syene and Alexandria, Eratosthenes determined the circumference of the Earth to be 250, 000 stadia. This value was a mere 1% off the exact value (Ast). Figure 3. Source: http://www.globalschoolnet.org/gsncenter/resources/articles/noonfigure3.jpg retrieved on 10 October 2009. Moreover, Eratosthenes made several significant contributions to astronomy, such as the measurement of the distance between the Earth and the Sun and that between the Earth and the Moon. He determined to a very great precision, the value of the tilt of the Earth’s axis, as 23° 51 15"; prepared a stellar map of 675 stars; and determined the obliquity of the Ecliptic. His poem Hermes comprises of a description of astronomy’s fundamentals. The addition of an extra day or leap day in leap years was one of his major suggestions (Ast). Important discoveries were made by Aristarchus in astronomy. His observations led him to conclude that the solar system was heliocentric. This was on the basis of his estimates of the relative sizes and distances of the Sun, Moon and the Earth. Although he had applied mathematically perfect techniques, the lack of sufficiently accurate astronomical instruments, resulted in approximate values. It was his estimation that the Sun was 20 times that of the Moon and 10 times the size of the Earth. He also believed that the Sun was 20 times farther away from the Earth than the Moon (Powell 52 – 54). Figure 4. Source: http://outreach.atnf.csiro.au/education/senior/cosmicengine/images/cosmoimg/aristarchus.gif retrieved on 10 October 2009. The celestial position of some 850 stars was accurately recorded by the Greek astronomer Hipparchus, around 150 BC. He was indefatigable in his astronomical efforts that he conducted from his Rhodes based astronomical observatory. In addition to recording the position of these stars, he also classified them on the basis of their magnitude or brightness. The axis of the Earth takes 26, 000 years to complete a complete circle. This is also known as the grand precession of the equinoxes. It was up to Hipparchus to determine that the annual shift in the Earth’s axis was 46 seconds of arc, in relation to the background of the stars. This value is not much different from the current value of 50.26 seconds of arc. This annual shift is termed as the precession of the Earth (Neugebauer 240 – 246). Hipparchus made a number of theoretical discoveries in astronomy, in addition to several practical innovations. In particular, he successfully applied geometric models, such as the eccentric and deferent epicycle. It is the firm belief of some scholars that the first catalogue of the stars had been prepared by this versatile Greek. Furthermore, he did considerable research on the length of the year, determining the lunar distance, and the calculation of eclipses (Neugebauer 240 – 246). Moreover, Hipparchus, studied the movement of the Sun and the Moon, and successfully proved that they performed uniform circular motion. His explanation of the movement of the points of solstice and equinox, from the east to the west is arguably his greatest discovery. Consequently, he was termed the discoverer of the precession of the equinoxes and the theory of trepidation (Neugebauer 240 – 246). Figure 5. Source: http://www.cam-cc.org/calendar/pic/back1.png retrieved on 10 October 2009. The Alexandria based Ptolemy was the last of the ancient Greek astronomers. He was actively involved in astronomical research around the year AD 140. He formulated a geometrical model of the solar system. This model could be employed to predict planetary position at any date and time. This remarkable model was in use for 1,400 years, till the time of Copernicus. Ptolemy assumed that each planet revolved in a small orbit or epicycle, in order to explain the intricate motion adopted by planets; which at times seemed to be travelling backwards in their own orbit (Lahanas). Figure 6. Source: http://www.vikdhillon.staff.shef.ac.uk/teaching/phy105/celsphere/phy105_ptolemy.html retrieved on 10 October 2009. Conclusion The Greeks as astronomers highlighted the importance of logical thinking and geometrical concepts in astronomy, rather than exclusive dependence on observation. This approach permitted the Greek astronomers to determine that the Earth circulated the Sun, the size of the Earth, and to establish that the Moon went around the Earth. It is the Greeks who explained eclipses and proved that the earth was spherical in shape. Work Cited Ast, Courtney. Eratosthenes. 10 October 2009 . History of Astronomy. 2009. 10 October 2009 . Lahanas, Michael. Astronomy of Ptolemy. 10 October 2009 . Lankford, John. History of astronomy: an encyclopedia. Routledge, 1996. Neugebauer, Otto. A history of ancient mathematical astronomy . Birkhäuser, 1975. Powell, Baden. History of natural philosophy from the earliest periods to the present time . Longman,Brown,Green & Longmans, 1837. "universe." 2009. Encyclopædia Britannica Online. 10 October 2009 . Read More