Astronomy is one of the oldest sciences that was founded in Ancient Greece. The beginnings of this science are much earlier but unification of all astronomical discoveries took place in Ancient Greece, so it’s accepted to consider this time the time of astronomy’s appearance. Metaphrase of the word “astronomy” from the Greek language means “the law of the stars”. Astronomy is the science of celestial objects such as stars, comets, planets and the cosmic radiation. Astronomy covers phenomena and objects outside the Earth’s atmosphere and its main subject is universe, its foundation and development, chemical and physical properties of stars, comets and other celestial objects. The relevant component of astronomy is astronomical observations, which also are necessary for the development of other science.
Nowadays some people think astrology and astronomy are similar concepts and it’s a great mistake. Astrology predicts people’s lives on stars, which are based on the motivation of celestial objects. Astronomy is based on the scientific method and doesn’t deal with any predictions. Astrology is practically the only science where amateurs can take part in important astronomical discoveries, especially in the observation of transitory phenomena.
The history of the development astronomy as a science is very interesting, it can be even divided into several periods. At first astrology was more astrometry, the main aim of which was to measure positions of the planets and stars in the sky and their motivation. Later with the works of Kepler and Newton, the mathematical predictions of stars and planets’ motivation took place. Solar system and celestial mechanics became the focus of astronomy. Nowadays astronomy is represented by theoretical astrophysics and observational astronomy.
The science of astronomy as we understand it now was developed by many philosophers and scientists during all the life of mankind. Aristotle, Ptolemy, Copernicus, Galileo and Newton have made a very important contribution to this science. Their discoveries were sometimes very similar, sometimes they were different or even contradicting, but they all, step by step, led to the development of astronomy.
Discoveries in astronomy
First generalized astronomical theory made Aristotel, who was the student of Plato and founded his own school of Natural Philosophy in 335 BC. This school got the name Lyceum. He was one of the most important ancient philosophers, who has made a lot of researchers in different areas of knowledge and his scientific inheritance is invaluable. Big part of the Western philosophy is based on writings made by Aristotle. He worked out different theories in the fields of astronomy, metaphysics, logic, physics and others. For more that two thousand years Aristotle’s astronomic theory was used till the Galileo’s discoveries added new facts to this science. The book “Aristotle’s physics” played the mankind a good service and became the foundation for the Ptolemaic planetary theory.
According to Aristotle’s theory the Earth was the center of the Solar System and it was immobile. By Aristotle the Four main components of the Earth were earth, water, air and fire that interacted and gave birth to everything in the Universe. This theory became the foundation for the church doctrine and was further worked over and improved by Ptolemy. Copernicus, Galileo and Newton’s theories are absolutely different and they completely refute the Aristotle’s one.
Astronomy is one of the oldest sciences of the world. Since ancient times people observed changes in the firmament and made their conclusions about the constitution of the Universe, time cycles, seasons, etc.
Aristotle explained his Cosmology in his books called On the Heavens and Physics. The main idea put forward in these books reflects his main concept of ordered Universe or Cosmos. Aristotle insisted on the importance of place to the contrast to the concept of space used before. He distinguished two main levels of existence – the Earth and the heavens. The Earth was the heaviest and the roughest substance and was situated in the center of the cosmos. Three substances, such as water, fire and air form shells around the fourth element – earth. All four elements that formed the Earth were similar in their essence and differed only in their qualities. Everything perfect, unchangeable and ideal belonged to the Heaven. Aristotle stated that the heaved was made out of substance called aether. Aether was the fifth element, which formed the Universe. He also stated that heavy bodies were situated inside the spherical shells of aether. Moon, Mercury, Venus, Sun, Mars, Jupiter, Saturn and stars were placed inside aether shells and situated in fixed stable order. According to Aristotle, each heavy body (star or planet) had a fixed orbit inside the aether sphere. He also called the prime mover the main and only reason of all rotations of the planets and stars in predetermined place with stable and never changing speed. He believed that the Universe was finite and there was nothing beyond the spheres with stars.
Ptolemy proposed his astronomical theory in the second century A.D. He used Hipparchus’s concept creating his astronomical theory. Scientists call sometimes Ptolemy “the father of astrology” for his great contribution when this science was only at the beginning of its development. He synthesized the knowledge of scientists who worked earlier. Ptolemy worked in the framework defined earlier by Aristotle. He added mathematical aspect to this science. He applied Euclid’s geometry as a part of astronomy, which gave new trends to this science. New system led him to the conclusion that all the planets moved around the Earth on a circle. But he also stated that in reality the Earth wasn’t in the center of the circles but that these circles were eccentric. His views were expressed in the work called Almagest. Ptolemy was the first scientist who noticed that planets rotated with different speed. This finally led him to the conclusion that planets moved on the semi-orbit. All his views were proved by changes in the speed of planet moves. He discovered changes not only in the speed of the planet move, but also in their direction. Some planets changed direction of their move and the system of their motion got the name retrograde motion. Ptolemy didn’t know that all planets have different speeds rotating on their orbits around the sun. From the earth it looked sometimes like planets changed the direction of their rotation and started to move back. So, Ptolemy didn’t get the essence of the problem calling the move of the planets retrograde motion but his observations about the difference in the speed of the planet move was very valuable. Most of the early astrological theories were geocentric. This means that scientists believed that the earth was in the center of the Universe and all the planets and starts were moving around it. The Church also adopted this view and it took several centuries to change the situation.
The first heliocentric theory was developed by Nicolaus Copernicus. Heliocentric theory gave simple and logical explanation to the retrograde motion. Nicolaus Copernicus explained the movements of the sun in the sky, the movements of the planets by the rotation of the earth together with other planets around the sun. He published his theories in the De Revolutionibus Orbium Celestium in 1953, the year of his death. Copernicus studied mathematics and astronomy at the University but worked as a physician and church administrator during all his life. His heliocentric theory reflected the needs of the time when previous geocentric theories were not sufficient any more. Copernicus agreed with the linear movements of the planets but placed the Sun in the center of the Universe. He also defined the right order of the planets starting from the sun.
Translated as the On the Revolutions of the Clestial Orbs, his book was a technical mathematical work with mathematical schemes and calculations in the tradition of Almagest, Ptolemy’s work on astrology. Despite his argument about the geocentric structure of the Solar system Copernicus insisted on the circular motion of the planets like his predecessors. His tables and schemes were more exact than those that had been developed before but still they were far away from perfect. The book caused a laud resonance in the society. Almost all the public, including scientists rejected his heliocentric model. But his schemes and calculations were so exact and precise that a lot of astronomers used them converting the models from heliocentric to geocentric ones. Despite the rejection of its main idea, De Revolutionibus became the most popular book among astronomers and was used for many years thereafter.
There were a lot of reasons Copernican heliocentric model was so difficult to accept. One of the main reasons was the adherence to the Aristotelian division to the Earth and Heavens and the idea that all heavy bodies (like earth, for example) possessed their natural place in the center of the Universe. It took almost one century to overcome this era. Accepting Copernican astrological theory meant not only change in the science but also the change of the whole philosophical system explaining the structure and functioning of the Universe. Copernican revolutionary ideas became a big achievement, which have changed the main dogmas of astrology forever.
Another revolutionary discoveries were made by Galileo Galilee. For his studies and observations he used telescopes of his own invention. The use of telescope gave him the opportunity to study the surface of the Sun and the Moon, discover satellites of Jupiter, phases the Venus went through, etc. Galileo put his idea in the small book called Starry Messenger. Published in 1610, this book very soon became very popular among astronomers and everybody interested in this science. These discoveries had a revolutionary meaning as they finally changed the whole philosophical concept of perfection and ideal of the Heaven. New findings proved that not only the Earth had satellites, rotating on their orbits and this proved that other planets had same features as the Earth.
Galileo came to the conclusion that the Copernican heliocentric model was more realistic that the Ptolemaic model. His views were expressed in the work called Dialogues Concerning the Two Chief World Systems published in 1632. “I hold that the Sun is located at the centre of the revolutions of the heavenly orbs and does not change place, and that the Earth rotates on itself and moves around it. Moreover ... I confirm this view not only by refuting Ptolemy's and Aristotle's arguments, but also by producing many for the other side, especially some pertaining to physical effects whose causes perhaps cannot be determined in any other way, and other astronomical discoveries; these discoveries clearly confute the Ptolemaic system, and they agree admirably with this other position and confirm it.” (Galileo, 78).
Such concept contrasted to the views on the Universe structure popular in the society of that time and expressed by the church. The reaction of the Church was aggressive as Galileo’s ideas contradicted to dogmas and norms proclaimed by the church of that time. The influence of the church was enormous during that time soon after publishing his book Galileo was called before the Italian inquisition. Church authorities, were no so loyal to Galileo as they used to treat Copernicus. For the Church of that time the most important question concerning the Copernicus system was whether it was just a mathematical system used for easier calculations or the complete system tending to explain the physical reality. In the case with Copernicus the Church was satisfied with the explanation that heliocentric theory was a mathematical one but the situation became quite different with Gallileo’s theory. Very soon after it was expressed in his works, it became evident that it went much further than a mathematical theory and that it threatened doctrines proclaimed by the Holy Scripture adopted by the church. In his Letter to the Grand Duchess Galileo attacked Aristotelian geocentric concept of the Universe structure.
He was made to disavow his work and his views. He was sentenced to the house arrest till the end of his life. Galileo had to obey the church but in reality he didn’t betray his principles and was sure in the heliocentric structure of the Universe. Another important input made by Galileo to the science of astrology was the discovery and study of the laws of fall and different kinds of motion.
This study was further developed by Newton, whose discovery of gravity became a breakthrough and gave new perspectives. Newton developed Galileo’s study of fall and gravity and applied it not only to the earth but also to the whole space and Solar system. He created the theory of the planetary motion, and discovered the law of gravity. He assumed and than proved the fact the intensity of gravity depended inversely on the square of distance, etc. Adding Kepler’s laws, discovered earlier to his new discoveries Newton formed his theory of the planetary motion. It was described in his work called “Principia”. Gravitation law applied to the planetary system stated that the motion of the planets was defined by the inertia -–going in the direction the used to move before and also the gravitation to the sun. His thesis gave additional proves to the heliocentric structure of the Universe but still there were a lot of astronomers, who still didn’t believe it. His rivals stated that if we take the concept that the earth moves around the sun for granted we have no way to explain the position of the starts, which look similar from the different parts of the Earth. It took several centuries to overcome these contradictions and to prove finally that Newton and all his predecessors who insisted in the heliocentric Solar system were right.
The structure of the Universe, the reasons and mechanisms of world functioning occupied the minds of people since ancient times and during the whole history of mankind there was made enormous number of effort to give this explanations. Aristotelian system called geocentric dominated during many centuries and was the most widespread explanation of the Universe structure. This system was developed and perfected by Ptolemy – another support of geocentric cosmology and one of the founders of astronomy. This concept, adopted by the Church dominated for many centuries in the society and in the minds of people. During the middle ages astronomy became the reason to go beyond the rigid limitation put by church. Revolutionary ideas put forward by Nicolaus Copernicus denied geocentric nature of the Universe destroying the myth that the earth was the center of the Universe made especially for man. According to Copernicus the sun was the center of the universe and the concept got the name heliocentric under the ancient name of the sun. This discovery became a great breakthrough not only in astronomy, but in the whole philosophical outlook of the mankind. But it became popular much later, after it was proved by Galileo and perfected by Newton. These scientists gave a considerable contribution and found a lot of facts proving the heliocentric structure of the Universe. Modern technique devices, such as telescopes used by Galileo and Newton broadened the opportunities for research and investigations putting them on more scientific basis.
1. Galileo Galilei, The Starry Messenger, translated by A. van Helden, Chicago 1989
2. Paul F. Grendler, The Roman Inquisition and the Venetian Press 1540-1605, Princeton 1977
3. Mary G. Winkler, and Albert van Helden, ‘Representing the Heavens: Galileo and Visual Astronomy’, Isis 83 (1992), 195-217, for the implications of representing telescopic observations.
4. Aristotle. The Complete Works of Aristotle: The Revised Oxford Translation. 2 vols., edited by Jonathan Barnes. Princeton: Princeton University Press, 1984.
5. Ariew, Roger. “Galileo’s Lunar Observations in the Context of Medieval Lunar Theory” Studies in History and Philosophy of Science, 15 (1984): 213-226.
6. Copernicus, Nicholas. On the Revolutions of the Heavenly Spheres. Translated with an introduction and notes by A. M. Duncan. London: David & Charles; New York: Barnes & Noble, 1976.
7. McClellan III, James E.; Dorn, Harold. Science and technology in world history: 404 pp., Baltimore: The Johns Hopkins University Press, 1999.