1 Ch. 3: The Solar System Brief outline: Ideas of Copernicus >> Galileo >> Kepler >> Isaac Newton This chapter discusses how the scientific contributions by Copernicus, Galileo and Kepler led to Newton's discovery of the Universal Gravitation. It must be understood that the ancient Greek philosophers-scientists had various opinions about the center of the universe and the relation between Earth and the Sun. Some thought that the Sun is at the center. Others that it is Earth. Aristotle (384-322 BC) chose to follow the opinion that it is Earth. It appears that he also believed that heavier bodies fall faster than light ones, and many other things. Much later in 312 AD Constantine was made emperor of Rome and protector of Christianity. Christianity evolved rapidly after the council of Nicaea (AD 325), when intellectuals/philosophers within the Catholic church made efforts to establish doctrine that would make the ideas found in the bible more complete, and eventually added concepts of both Plato and then Aristotle. Once this was done it became DOGMA of the church, and to attack this view was to attack the foundation of the church. And so this incorrect view lasted for over 1,000 years, until Copernicus. <Nicolaus Copernicus> (1473-1543) Ideas The earth is NOT the center of the universe, although it is the center of the moon s orbit and of its own gravity. The sun is the center of the planetary system and the sphere of stars. Earth is just one of the planets. Since the moon rotates around the Earth, the heavenly bodies do not share the same center. The Earth s distance from the sun is negligible compared to the distance to the fixed stars. The stars, therefore, are vast objects lying at great distances from the Sun and the Earth.
2 Although the heavens appear to rotate around the Earth once a day, it is the Earth that rotates on its own axis. The Sun appears to move completely around the sky once a year, but this is due to the revolution of the Earth around the Sun. The complex movements of the planets, which include points of apparent rest and periods when they seem to reverse their normal march across the sky (retrograde motion), along with their brightening and dimming, can be explained by the relative motions of each planet & The Earth. Placing the sun at the center resolves all ambiguities about the order of the planets. The further the orbits from the sun, the longer they take to circle it. Mercury is the closest and in the least time, 88 days, while distant Saturn takes 30 years to circle the sun. Method Few astronomical observations Relied more on ancient and unreliable sources. Was put off by a basic inconsistency Was very conservative Feared scorn Appreciated orders Was very cautious of his ideas His theories were based on knowledge of his predecessors. Lack of vision, brilliance, fire. Was fearful, stubborn, miserly, obsequious to authorities, arrogant toward others, and a procrastinator. Impact Overturned two thousand years of astronomical thinking (perception that the earth stands still while the heavens wheel around it) Gave birth to our present concept of the solar system. Galileo, Kepler and Newton built on his foundation (De Revolutionibus) and their work cumulatively destroyed the ancient view of a finite, womb-like cosmos with the Earth & The Human Race at its center. <Johannes Kepler> (1571-1630) Ideas Kepler (eventually) managed to get access to the observational equipment of Tycho Brahe (1546-1601), a very wealthy guy who loved astronomical observations and made very careful and accurate observations of the planets daily. Kepler needed this data to formulate his three rules of planetary motion around the Sun. The Universe was constructed on the basis of Geometric figures.
3 Three laws of planetary motion o Confirmed Copernicus s heliocentric theory while modifying it in some way. First Law - The orbits of the planets around the sun were not circular but elliptical in shape with the sun at one focus of the ellipse rather than at the center. o Rejected Copernicus Second Law - The speed of a planet is greater when it is closer to the sun and decreases as its distance from the sun increases. o Destroyed a fundamental Aristotelian Tenet that the motions of the planets were steady and unchanging. Third Law - Planets with larger orbits revolve at a slower average velocity than those with smaller orbits. Method Great interest in Math and Astronomy Was an avid Astronomer Keen interest in Hermetic thought and Neoplatonic mathematical magic Modification Observation Solid Evidence Impact The three laws effectively eliminated the idea of uniform circular motion as well as the idea of crystalline spheres revolving in circular objects. People had been freed to think in new terms of the actual paths of planet revolving around the sun in elliptical orbits. Caused the Ptolemaic system to rapidly lose ground to new ideas. Important questions still remained unanswered: What were the planets made of?! And how does one explain motion in the universe - led to Galileo Galilei to answer.
4 <Galileo Galilei> Ideas Observed sunspots - The Universe is not unchanging The moon was just like the surface of the Earth as it had mountains and depressions. Invented the telescope Milky Way had separate stars. Jupiter was like a miniature planetary system. Charted the orbits of its moons Designed instruments such as a thermometer and a mechanical calculating device, his geometric and military compass. A nova or a new star, in the constellation Serpentarius, lay in the supposedly unchanging regions beyond the moon. Scribed phases of Venus Rotation of the sun The Copernicus theory was true. Outlined and explained the scientific method in his book The Assayer. In it, Galileo set out his views on scientific reality and on the new scientific method; he explained his doctrine of primary qualities (which were those that could be measured) and secondary qualities (which were not measurable, i.e. qualities like odor and taste). In The Assayer, he also explained how to define a problem with the help of preliminary experiments and, from the results, to form a theory, which could then be used to predict consequences that could be observationally tested. It was in The Assayer, too, that he made his famous remark, The Book of Nature is... written in mathematical characters. Published the Starry Messenger in Italian (instead of Latin - the language of the learned) which helped in the spread of the observations he made using his telescope. NOTE: He did not mention about the heliocentric universe in the Starry Messenger. He supported the heliocentric universe in his another publication the Dialogue Concerning the Two Chief World Systems.
5 Method Proved or disproved competing theories not just through logic but through experimentation. - Father of Modern Science/Father of Mathematical Physics - invented the scientific method which was later refined by Isaac Newton Realized that Science must be built on measurement & Mathematics Observations Careful Drawing Insisted on writing in Italian rather than Latin - More spread of his ideas Bold & Expansive mind, indefatigable observation & experimentation Impact He turned Copernicus s heliocentric theory into demonstrate able fact. His careful drawings of Jupiter s retinue of moons, phases of Venus, and spots defacing the Sun, made the issues on the truth real. Cast doubt on people about the Earth s position & God s location. Broadcasted his radical ideas to the masses Casted the church to be under doubt. It was no longer mathematics. Either the Earth and Humanity lay at the center of creation as the Church decreed or they wandered insignificantly through space. His pugnacious courage, blazed on indelible trail for all scientists to come.
6 <Sir Isaac Newton> Ideas The three laws of motion: 1) Every object continues in a state of rest or uniform motion in a straight line unless deflected by a force 2) The rate of change of motion of an object is proportional to the force acting upon it. 3) To every action, there is always an equal and opposite reaction. Demonstrated that the three laws of motion govern the planetary bodies as well as terrestrial objects Universal law of gravitation (in his Mathematica Pricipatia): Every object in the Universe was attracted to every other object with a force (gravity) that is directly proportional to the product of their masses and inversely proportional to the square of the distances in between them. Method Interest in Mathematics, Invention and philosophy. Extreme interest in aspect of the occult world. Was not the first of reason, was last of magicians. Believed that clues about mysteries about the world were to be found partly in evidence of the heavens and in the construction of elements, but also partly in certain papers or traditions handed down from the past. Considered himself a representative of the Hermetic Tradition. Spelled out the Mathematical Proofs showing his Universal laws of Gravitation His work was the culmination of the theories of Copernicus, Galileo, and Kepler. Applied his theories of mechanics to the problems of astronomy.
7 Impact 1666 Invented the calculus Investigated into the composition of light Inaugurated his work on the law of Universal Gravitation 1684 Wrote the Principia (Mathematical Principals of Natural Philosophy) 1686 Pieced together a coherent synthesis for a new cosmology. Demonstrated that one universal law mathematically proven could explain all motions in the universe. Gave the idea that The Secrets of the natural world could be known by human investigation. Created a new cosmology in which the world was seen largely in mechanistic terms. The world view of the West was dominated by Newton s world-machine, conceived as operating absolutely in time, space, & motion, until the 20th century. Ideas were soon accepted and reinforced by developments into their fields especially medicine.
. 6.24 (CP): A summary of the process by which our solar system formed, according to the nebular theory. 8
Materials in the solar nebula. 9
Fig. 6.17 (CP): Temperature differences in the solar nebula led to different kinds of condensed materials, sowing the seeds of two different kinds of planets. 10
Illustration of the asteroid belt, Kuiper belt & Oort cloud 11
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Things that are moving rapidly across the night sky can be: bird, plane, satellite, Superman or meteoroid: comet or asteroid 15