Historical Views of Our Solar System

The early views of the solar system were guided by philosophy and religion more than mathematics. Most of the universe's structure was pondered upon philosophically through mysticism rather than logical derivation. The Greeks believed that the earth was round, but it wasn't until Aristotle (560-480 BC) that actual observational evidence was used to proof that the earth was spherical. Natural Philosophers (scientists) of the time began to explore how the solar system was structured and developed models to explain our universe. The idea that the sun is the center of the solar system was not discovered by renaissance astronomers, but rather hypostulated in 300 BC by Aristarchus of Samos. Aristarchus was a Greek astronomer who attempted to measure the relative distances and sizes of the earth, moon, and sun. Although his measurements were not very accurate he did propose that the sun was larger then the earth. This revelation made him consider that the sun was the center of the solar system (heliocentric). At the time the populous viewed the earth as center of the universe because why would the gods create the center of civilization on the earth, but not make it the center of the solar system. Also as people observe the sky they see that everything passes from east to west, which seems to make everything look like it is rotating around the earth. When Aristarchus presented his view of a sun centered solar system, astronomers were skeptical and quickly developed a logical argument, parallax, that regrettably hindered astronomical advancement for the next 1800 years. Parallax is the apparent movement of a stars position in the sky due to the earth's orbit around the sun. When an astronomer views a star in January it should seem to be in a different position then when it is viewed in June. Astronomers used this reasoning against Aristarchus' argument for the sun centered solar system. The Greeks attempted to observe parallax with the best instruments of their day, but they did not observe any parallax. Unfortunately they believed in falsificationism, which is the philosophy that if one experiment disproves a theory then that theory is false, this lead 1800 years of astronomical research down the wrong path. As it turns out parallax is true, but requires observation from a powerful telescope with extremely precise measurement and it wasn't until 1838 that the first parallax was measured.

Astronomers from that moment on considered the earth to be the center of the solar system (geocentric). All the observable objects in the sky were fixed into transparent spheres which rotated about a single fixed point, a non-rotating earth. At the time the Moon, Venus, Sun, and Mars were viewed as planets that were fixed in the rotating spheres. The change from night to day was a separate shell that rotated about the earth bringing about darkness and light. The rest of the stars were fixed in a outer shell, which was surrounded by nothingness.

fThe geocentric view had many physical problems associated with it. The largest problem was with retrograde motion, which is when a planet is traveling along in its orbit and then it seems to suddenly reverse direction and begin to travel back along its original path in the opposite direction. Ptolemy (100-170 AD) developed a model involving a small circle, called an epicycle, that rotated on a bigger circle. A planet was fixed on this epicycle plane, which spins on it's own axis, which in turn is fixed to another circle that spins around the earth. Ptolemy's model quite accurately predicted the motion of the planets. There were other problems with the the geocentric model and complicated theories were developed to fix them. The complexity of the geocentric model increased with passing time to the point where philosophers began to introduce theories about simplicity, Ockham's Razor for example. If it were not for the Catholic Church the heliocentric solar system would have re-emerged as the dominate view.
Many scientists recognized that the complexity of the solar model was increasing with each new discovery. It was not until a lawyer, studying astronomy in his free time, finally decided to muster the courage and announce that the Sun was the center of the solar system. In his book De Revolutionibus Orbium Coelestium, published in 1513 AD, Nicolaus Copernicus firmly proved that the complicated geocentric view fails and that the Earth is a satellite orbiting the Sun. The Roman Catholic Church did not desire this view to be released to the public because it had adopted the Ptolemy view of the solar system. The church did not believe that the sky was changing and it took a strong stand against anyone who opposed this view. Many scientists that antagonized the authority of the church were imprisoned or burned at the stake during the inquisition. The book was entered into the Index of Banned Books in 1616 and it remained on that list until 1835. Copernicus and Aristarchus were not the only people to believe in the heliocentric view, but due to the fear of the Roman Catholic Church, scientists did not want to be labeled as heretics and be brought in front of the Inquisition. If it were not for the adoption of the “teleological view of divine creation” by the church, the heliocentric view would have emerged sooner.
The scientific community was hesitant to accept the heliocentric view and enormous amounts of calculations and observations were required to prove it, but it did not predict the orbits of the planets with any more precision than Ptolemy’s epicycle model. There was one minor flaw in Copernicus’ work that diluted its powerful message, he assumed that all the planets orbited around the sun in circles. It wasn’t until 1609 that Johannes Kepler discovered the real orbit geometry of planets. Kepler worked with Tycho Brahe who, due to his royal blood and inherited wealth, did not need to work and decided to devote his life to taking accurate measurements and observations of the universe. Using Brahe’s extensive data Kepler observed that the planets rotated about the sun in ellipses and their orbit was proportional to their period of rotation around the sun. He developed three laws about the motion of satellites around their primary member and his laws serve as the base point for orbital mechanics. Kepler was able to publish and speak about his work with more freedom than his predecessors were due to the Protestant movement throughout Germany and England. The mathematical soundness of the orbital trajectories of planets was added to Copernicus’ heliocentric solar system making it become more popular, but one more scoop of ice cream on this sundae was needed to make this view gospel.
The final piece to proving the Copernican theory occurred in 1609 when Galileo developed the first astronomical telescope. This was not a revolutionizing piece of equipment because lenses had already been invented and people constructed telescopes to survey and look at objects on the ground, but Galileo was the first to actually point it toward the sky giving birth to the astronomical telescope. Using his quasi-invention, Galileo discovered four moons orbiting about Jupiter and this observation proved that not everything in the universe orbited around the Earth. Galileo in 1632 published his findings in his book Dialogue Concerning the Two Chief World Systems, in which he argued for the heliocentric system. The Catholic Church became worried of this publication because of its content and that it was written in Italian rather than Latin. Up until this publication all books were written in Latin so that only the most educated of people could read them. A book written in Italian could have been read by an educated commoner, which could open his eyes to his oppression and the truth. The Church demanded that Galileo denounce his writings and they imprisoned him until his death. His publication was the final piece to the puzzle of the heliocentric system. Through pain and sacrifice, the collected works of scientists have developed the way we view the universe we live in.

References:

Explorations: An Introduction to Astronomy, Thomas T. Arny. 3th Edition. 2002 McGraw-Hill
http://es.rice.edu
http://www.mhs.ox.ac.uk
http://zebu.uoregon.edu
http://www.eyewire.com
http://www.biblicalastronomer.org
http://capa1.physics.sunysb.edu

J.A. Taylor