Directions: Read the following introduction and take notes in your notebook. Then download the video guide linked below and answer the questions on the worksheet from the video.
Ptolemy's universe, illustrated in 1559. Artistic licence has added scenery and the figure of Atlas supporting the structure. Strictly speaking there was held to be nothing beyond the outermost sphere but God's invisible presence.
Aristotle's cosmological system, which had survived almost intact for two thousand years, was based on a common-sense view of the universe. To the ordinary observer the sky seems to move. The stars, whose positions never change, wheel past every night. At the Pole they never disappear, circling round the North Star. Among the fixed stars five wandering lights, called planets from the Greek word for 'wanderer', can be seen. The moon circles the earth, as does the sun. Aristotle explained these phenomena by means of a cosmological system made up of eight crystalline spheres on which the sun, moon, planets and stars were each fixed. These spheres rolled eternally round the earth, which did not move. Moreover, while the sky was evidently perfect and unchanging, earth was not. Terrestrial things decayed and died. All motion on earth was straight-line motion, manifested by the vertical manner in which objects sought their 'preferred' position, the lowest they could find. |
In the sky the perfect, eternal motion of the stars was circular. The spheres were composed of ether, a substance which could neither be destroyed nor changed into anything else. This was the fifth element. The other, terrestrial, elements were earth, water, air and fire. The heavens were incorruptible because their motion was circular and so they never suffered 'forced' movement. On earth, any natural movement occurred in straight lines, although the natural state of things was at rest. Any movement on earth was, therefore, forced movement, except for that of the four elements. Air and fire, being light, rose. Earth and water, being heavy, sank. All things were made up of these four elements and decayed because they were frequently subjected to forced movement.
A gunner fires his cannon according to the laws of Aristotelian physics: the ball can only move up or down in straight lines. The earth was a sphere, because that was a perfect shape and because its shadow could be seen on the moon. The earth stood still because had it moved this would have been due to either natural or forced movement. Forced movement destroyed things and the earth still existed, so whatever movement there might be would have to be natural. The only natural movement possible on earth, however, was movement straight to the center of the earth. If the earth turned or moved in any way this would presuppose two natural movements. The only possible explanation was that the earth stood still. This view was, of course, supported by the Bible.
There were obvious anomalies in this system, which made things difficult for the Church. Over the centuries it had explained them in various ways. The principal irregularity was visible to the naked eye. There were occasions when the planets changed course: Mars, for instance, would sometimes stop and go backwards. Given a system in which the celestial spheres could not change direction the only convincing explanation was that put forward by the Alexandrian astronomer Claudius Ptolemy in the second century. In his view each planet turned on a small sphere fixed to the main one. To the earthly observer there would be times in such a system when the combinations of turning sphere and turning mini-sphere could cause aberrations in planetary motion. Ptolemy called the movements which took place on the mini-spheres 'epicycles.'
The problem of calendar reform involved all these phenomena and the accepted explanations of why they occurred, since the cosmos and everything in it was a manifestation of God's plan. Belief in Aristotle and Ptolemy was the bedrock of social stability.
The problem of calendar reform involved all these phenomena and the accepted explanations of why they occurred, since the cosmos and everything in it was a manifestation of God's plan. Belief in Aristotle and Ptolemy was the bedrock of social stability.
The Day the Universe Change, Infinitely Reasonable - James Burke
|
|