7/14/06ISP 209 - 3A3 The solar system Sun Planets Asteroids Comets Pluto Neptune Uranus Saturn Jupiter Mars Earth Venus Mercury Sun
7/14/06ISP 209 - 3A4 Historical figures in the Copernican Revolution Ptolemy – the geocentric model, that the Earth is at rest at the center of the Universe. Copernicus – published the heliocentric model. Galileo – his observations by telescope verified the heliocentric model. Kepler – deduced empirical laws of planetary motion from Tycho’s observations of planetary positions. Newton – developed the full theory of planetary orbits.
7/14/06ISP 209 - 3A9 The reasons for seasons – the Earth travels around the sun, and its axis of rotation is tilted by 23.5 degrees to the plane of the orbit. In July, the northern hemisphere is getting more sunlight than in January. The heliocentric model
7/14/06ISP 209 - 3A14 Galileo’s discoveries in Astronomy Galileo did not invent the telescope, but when he heard about the invention he figured out how to build telescopes. He had the best telescopes of his time. He was the first person to use telescopes to look at the heavenly bodies. He was first, so he made the discoveries. Craters and mountains on the moon Moons of Jupiter Phases of Venus The Milky Way consists of innumerable stars. Sunspots move across the sun’s face. All of these favored the Copernican (heliocentric) model.
7/14/06ISP 209 - 3A15 Galileo’s sketch of the moon as seen from his telescope A photograph of the moon “What do you think of the foremost philosophers of this university? In spite of my oft repeated efforts and invitations, they have refused, with the obstinacy of a glutted adder, to look at the planets or Moon or my telescope.” (letter to Kepler)
7/14/06ISP 209 - 3A16 Galileo made many specific discoveries in astronomy, through observations by telescope. The general implications… ● The planets are objects like the Earth – masses – rather than some kind of special heavenly objects. Or, to put it another way, the Earth is just another planet. ● The planets, including Earth, travel around the sun. ● The Universe is a lot bigger than we can see by the naked eye. These ideas could be dangerous.
7/14/06ISP 209 - 3A17 His Church decided that the heliocentric model was a heresy. But Galileo continued to argue in favor of the theory, and published his reasoning. The Inquisition in Rome accused him of heresy, and required him to answer. Found guilty of “suspicion of heresy,” Galileo recanted publicly. [A story, probably not true, is that he muttered “Eppur si muove” – “And yet, it does move.”] He was put under arrest and sentenced to prison. But because of his fame and age (70 years old at that time) he was allowed to serve under house arrest in Florence, for the remaining years of his life. The Trial of Galileo
7/14/06ISP 209 - 3A18 Is there a conflict between Science and Religion? There is no major conflict today, but there have been conflicts in the past, e.g. the trial of Galileo. Another example is the conflict between Darwin’s theory of evolution and the literal interpretation of the Book of Genesis ( ). That latter conflict survives today in the controversy about teaching Creationism in public schools. Pope John Paul II ordered a review of the trial of Galileo. Did the Inquisition make mistakes?
7/14/06ISP 209 - 3A19 Their work was finished in 1992. On October 31st, Cardinal Poupard delivered the final report during a papal audience. The fifth paragraph reads: “Certain theologians, Galileo’s contemporaries, being heirs of a unitary concept of the world universally accepted until the dawn of the seventeenth century, failed to grasp the profound, non-literal meaning of the Scriptures when they described the physical structure of the created universe. This led them unduly to transpose a question of factual observation into the realm of faith. It is in that historical and cultural framework, far removed from our own times, that Galileo’s judges, unable to dissociate faith from an age-old cosmology, believed quite wrongly that the adoption of the Copernican revolution, in fact not yet definitively proven, was such as to undermine Catholic tradition, and that it was their duty to forbid its being taught. This subjective error of judgment, so clear to us today, led them to a disciplinary measure from which Galileo had much to suffer. These mistakes must be frankly recognized, as you, Holy Father, have requested.” (L’Osservatore Romano, November 1, 1992)
7/14/06ISP 209 - 3A20 Science and Religion Modern science has discovered that the Earth and solar system have changed dramatically in time, over a period of billions of years since its creation. Age of Earth ~ 4.5 Gy Geological processes Ice ages Biological evolution This scientific understanding conflicts with a strict literal interpretation of the Book of Genesis. But science does not know (maybe cannot know) how the universe was created. Each person must decide what to believe, but may not impose his beliefs on others.
7/14/06ISP 209 - 3A21 Johannes Kepler (1571 – 1630) … discovered three empirical laws of planetary motion in the heliocentric solar system 1.Each planet moves on an elliptical orbit. 2.The radial vector sweeps out equal areas in equal times. 3.The square of the period is proportional to the cube of the radius. (needed for the CAPA)
7/14/06ISP 209 - 3A22 How did Kepler determine the planetary orbits? Compare the heliocentric model to naked-eye astronomy The most complete data had been collected over a period of many years by Kepler’s predecessor, Tycho Brahe of Denmark. The inner planet is Earth; the outer one is Mars. Plot their positions every month. Mars lags behind the Earth so its appearance with respect to the Zodiac is shifting. Earth Mars
7/14/06ISP 209 - 3A23 Astrology… a persistent superstition It’s all nonsense, of course. The motions of the planets are prescribed by natural laws of motion and gravity. How can their motion predict the future?
7/14/06ISP 209 - 3A24 Ellipse Geometry To draw an ellipse: Take a string. Tack down the two ends. Put a pencil in the string and pull the string taut. Move the pencil around keeping the string taut. An ellipse is the locus of points for which the sum of the distances to two fixed points is fixed. The two fixed points are called the focal points of the ellipse.
7/14/06ISP 209 - 3A25 Parameters of an elliptical orbit (a,e) ► Semi-major axis = a = one half the largest diameter ► Eccentricity = e = ratio of the distance between the focal points to the major diameter For example, this ellipse has a = 1 and e = 0.5. Perihelion = r2 = 0.5 Aphelion = r1 = 1.5 ► Perihelion and aphelion
7/14/06ISP 209 - 3A26 Example. Determine a, e, r1, r2.
7/14/06ISP 209 - 3A28 The observed solar system at the time of Newton Sun Mercury Venus Earth Mars Jupiter Saturn (all except Earth are named after Roman gods, because astrology was practiced in ancient Rome) Three outer planets discovered later… Uranus (1781, Wm Herschel) Neptune (1846 Adams; LeVerrier) Pluto (1930, Tombaugh)
7/14/06ISP 209 - 3A29 To explain the motion of the planets, Newton developed three ideas: 1.The laws of motion 2.The theory of universal gravitation 3.Calculus, a new branch of mathematics Newton solved the premier scientific problem of his time --- to explain the motion of the planets. Isaac Newton “If I have been able to see farther than others it is because I stood on the shoulders of giants.” --- Newton’s letter to Robert Hooke, perhaps referring to Galileo and Kepler m F a 2 21 r mGm F
7/14/06ISP 209 - 3A30 Newton’s Theory of Universal Gravitation Newton and the Apple (The apple never fell on his head, but sometimes a stupid person will say that, trying to be funny.) Newton asked good questions the key to his success. Observing Earth’s gravity acting on an apple, and seeing the moon, Newton asked whether the Earth’s gravity extends as far as the moon.
7/14/06ISP 209 - 3A31 Quiz Question Who discovered that the orbit of a planet is an ellipse?