Models of the Solar System The Development of Understanding from Ancient Greece to Isaac Newton
Aristotle (384 BC 322 BC) Third in line of Greek thinkers: Socrates was the teacher of Plato, Plato was the teacher of Aristotle. Aristotle s Model was an earthcentered, spherical universe. Earth was made of 4 elements (earth, water, air, fire) which moved in straight lines to find their natural resting places. The Heavens, or aither, moved in perfect circles around the earth.
Aristarchus of Samos (310 250 BC) Greek astronomer who was the first to assert that the earth revolves around the sun. His beliefs are only known due to writings of his younger contemporary, Archimedes. Theories were grounded in scientific observation and mathematics. His theories were not well accepted, as Aristotle s idea that the sun revolved around the earth was well accepted. Developed a very simple form of calculus, mastered by Newton 2000 years later.
Ptolemy (87-150 AD) Greek Astronomer, mathematician, geographer. Promoted Greek Geo-centric model of Solar System, but elaborated on theory to account for apparent retrograde or backward motion of planets. Proposed epicycles of planets: planets orbit the earth in circles but follow smaller circular paths while in their larger orbit.
Ptolemy s Model
Nicolaus Copernicus (1473-1543) Polish astronomer, famous for his heliocentric model of the solar system. His theory was that the sun is at rest near the center of the universe, and the earth, spinning on its axis each day, revolves annually around the sun. Published his theory in De Revolutionibus Orbium Celesium in 1530. Translated to On the Revolution of the Heavenly Spheres. Added new meaning to the word revolution.
Copernicus Model Only supported by about 10 others including Galileo and Bruno; political and religious price too high for most to embrace. (Bruno was tried, condemned, and burned at the stake in 1600; Galileo forced to renounce his beliefs in 1633 and died under house arrest.)
Tycho Brahe (1546-1601) Danish Astronomer known for excellent observational skills. While he was studying at the University of Wittenberg, Brahe had a duel with another student about who was the best mathematician. Brahe had his nose cut off, and for the rest of his life wore a silver nose. Hired by King of Denmark to be royal astronomer in 1574; was given an island and built the finest observatory in Europe.
Brahe s Model Promoted a geocentric model, with the sun orbiting the earth. Observation fit Copernicus idea of planets orbiting sun, so Brahe compromised with his own theory. 5 known planets orbit the sun, and this whole system orbits the earth once per year. Designed, built, calibrated and maintained the instruments that he used every night for astronomical observations. Hired Johannes Kepler to help in the observatory in 1600; Died a year later in 1601.
Johannes Kepler (1571-1630) German astronomer and natural philosopher. Chair of astronomy and mathematics at University of Graz (Austria) from 1594 to 1600, when he became assistant to Tycho Brahe. Stole Brahe s data, after he died, to formulate his three laws of planetary motion. Even though he had many positions as state and royal mathematician, he was poorly paid and lived in poverty all of his life.
Kepler s Laws The planets move in ellipses with sun at one focal point. In their orbits about the sun, the planets sweep out equal areas in equal times.
Galileo Galilei (1564 1642) Italian physicist and astronomer, who verified the heliocentric model with observations. Heard of the invention of the telescope; invented his own (without seeing one) and witnessed the moons of Jupiter and phases of Venus. Galileo supported Copernican view of circular planetary orbits, but he completely ignored Kepler s ideas. The catholic church conceded that Galileo was correct in 1992!
Isaac Newton (1642 1721) Born Christmas Day in England, in the same year Galileo died. During plague, Cambridge was closed. Spent 1665 and 1666 working on problems in physics and mathematics. Came up with his three laws, Calculus, and law of Universal Gravitation. Believed in Copernican, and then Keplerian, model of solar system.