Helio vs geo 2
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No, the Sun is not the center of the Universe. The Copernican model established that the Earth and planets orbit the Sun, but the Sun is just one star among billions in the Milky Way galaxy, which itself is one of trillions of galaxies in the observable universe.
Helio vs geo 2
- 1. The Copernican Revolution The Birth of Modern Science 1
- 2. What do we see in the sky? • The stars move in the sky but not with respect to each other • The planets (or “wanderers”) move differently from stars – They move with respect to the stars – They exhibit strange retrograde motion • What does all this mean? • How can we explain these movements? 2 • What does the universe look like?
- 3. Geocentric vs. Heliocentric • How do we decide between two theories? • Use the Scientific method: – These are both explanations based on the observation of retrograde motion – What predictions do the models make? – How can these predictions 3 be tested?
- 4. Geocentric vs. Heliocentric Models of the Solar System Ancient Greeks knew of Sun, Moon, Mercury, Venus, Mars, Jupiter and Saturn. Aristotle vs. Aristarchus (3rd century B.C.) Aristotle: Sun, Moon, Planets and Stars rotate around fixed Earth. Aristarchus: 1st Heliocentric model Aristotle: But there's no wind - Doesn’t “feel” like we are moving. (Actually orbiting sun at 70,000 mph!) Difficulties with "Geocentric" model - Retrograde motion of planets - Phases of Venus 4
- 5. Geocentric Model of Solar System (Earth Centered) What are some reasons that the geocentric model of the universe seems to make intuitive sense? It doesn't feel like we are moving – wouldn't there be a wind or something? Why would things fall down and not towards the center of the universe? Why don't we see stellar parallax? 5
- 6. GeoCentric 6
- 8. Geocentric Model (Earth Centered) • Fairly good agreement with retrograde motion of planets • Some predictive power • More precise measurements showed errors • To account for unusual planetary motion epicycles were introduced • Fit the Greek model of heavenly perfection – spheres are the perfect shape, circular the perfect motion 8
- 9. Ptolemy’s Prediction: Future planetary positions Observation: retrograde motion of planets Refine: epicycles Success! For 1500 years 9 cfa-www.harvard.edu/seuforum/mtu/MTUcosmology.ppt
- 10. Motion of the other planets Mars Retrograde Motion 10
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- 12. 12 Ptolemy's geocentric model (A.D. 140) (VIDEO CLIP)
- 13. Ptolemy’s system provided the first framework for all discussion of the universe for nearly 1500 years!! But… there was a problem Problems with Geocentric Theory 1. This model does not explain all apparent motions of celestial (space) objects 2. Cannot explain Foucault’s Pendulum or the Coriolis Effect 13
- 14. Geocentric model fails to account for phases of Venus 14
- 15. Aside: Aristarchus - Written in the second century BC he calculated the ratio of the distance between the Earth and Sun to that between the Earth and the Moon. (His estimate was more than an order of magnitude too small, but the fault was in his lack of accurate instruments rather than in his method of reasoning.) -This image compares the line subtending the arc dividing the light and dark portions of the Moon in a lunar eclipse with the relative diameters of the Moon and Sun. -Aristarchus also found an improved value for the length of the solar year. 15
- 16. Geocentric vs. Heliocentric • Against heliocentric – It predicted planetary motions and events no better than the Geocentric system – The earth does not move (things do not fly off) – The earth is different from the heavens (from Aristotle – the heavens are perfect and unchanging) and cannot be part of the heavens • For heliocentric – Simplified retrograde motion, but epicycles were necessary to account for the planets’ changing speed – The distances to the planets could be measured. These distances were ordered, and therefore aesthetically pleasing to the philosophy of the day16
- 17. Heliocentric (Copernican) System • Sun at center (heliocentric) • Uniform, circular motion – No epicycles (almost) • Moon orbited the earth, the earth orbited the sun as another planet • Planets and stars still on fixed spheres, stars don’t move • The daily motion of the stars results from the Earth’s spin • The annual motion of the stars 17 results from the Earth’s orbit
- 18. Heliocentric model easily accounts for phases of Venus 18
- 19. Timeline Tycho Galileo 1473-1543 1546-1601 1571-1630 1564-1642 1642-1727 Copernicus Kepler Newton
- 21. Heliocentric Model “Rediscovered” by Copernicus in 16th century. Copernicus 1473-1543 Much simpler was the main attraction for Copernicus. Simply explains retrograde motion. Put Sun at center of everything, but still insisted on circles, thereby retainig unnecessary complexity. Opposed by Catholic Church Copernican revolution – critical realization that Earth is not at the center of the universe, only accepted after his death.
- 23. • In the heliocentric model, apparent retrograde motion of the planets is a direct consequence of the Earth’s motion
- 24. Retrograde Motion of Planets Earth overtakes slow outer planet so the outer planet appears to slow down, move in reverse, and then move forward again with respect to the fixed stars Planets sometimes appear to loop back - retrograde motion Loops are called "epicycles" July Mars 7 Earth * 7 6 6 * 5 Apparent motion of 3 * Mars against 4 4 * * "fixed" stars 3 5 2 2 24 1 * 1 January
- 25. Stellar Parallax • Parallax caused by the motion of the earth orbiting the Sun • Not observed with the naked eye • The heliocentric model predicts stellar parallax, but Copernicus hypothesizes that the stars are too far away (much farther than the earth from the Sun) for the parallax to be measurable with the naked eye
- 26. Parallax • Triangulation - Measure angles at points A and B • Parallax - Know Baseline. Measure third angle in triangle made by A, B, and object in space – Baseline problem 26 The apparent displacement (shift) of a foreground object relative to the background as the observer’s location changes is known as parallax.
- 27. Misconceptions 1. The Copernican model has a force between the sun and the planets. Actually, the natural motion of the celestial spheres drove the planetary motions. 2. The Copernican model was simpler than the Ptolemaic one. In fact, though Copernicus eliminated circles to explain retrograde motion, he added more smaller ones to account for nonuniformities of planetary motions. 3. The Copernican model predicted the planetary motions better. Because both models demanded uniform motion around the centers of circles, both worked just about as well – with errors as large as a few degrees at times.
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- 29. Tycho Brahe (1546-1601): the greatest of the pre-telescope observers in Europe. 20+ years measuring the positions of the Sun, Moon and planets with great accuracy.
- 30. Tycho Brahe • Had two sets of astronomical tables: one based on Ptolemy’s theory and one based on Copernicus’. • He found that both tables’ predictions were off by days to a month. • He believed that much better tables could be constructed just by more accurate observations. • Tycho’s homemade instruments improved measurement precision from ten minutes of arc (which had held since Ptolemy) to less than one
- 31. The skies change Tycho observed 2 phenomena that showed the heavens DO change: – In November 1572, Tycho noticed a new star in the constellation Cassiopeia – Comet of 1577 • Prior to this sighting, comets were thought to be atmospheric phenomena because of the immutability of the heavens • But neither the star nor the comet changed position as the observer moved, as expected for atmospheric phenomena
- 32. • Johannes Kepler (1609) • Johannes Kepler was an assistant to Tycho Brahe. He used Brahe’s observations to study the orbit of Mars • Discovered three laws of planetary motion: predict with accuracy the motions of the planets 36
- 33. Johannes Kepler • Kepler succeeded Tycho as the Imperial mathematician (but at only 1/3 the salary of the nobleman) • Kepler worked for four years trying to derive the motions of Mars from Brahe’s observations • In the process, he discovered that the plane of the earth’s orbit and the plane of Mars’ (and eventually the other planets) passed through the sun • Suspecting the sun had a force over the planets, he investigated magnetism • While this is not true, it did lead him to the idea of elliptical orbits • “With reasoning derived from physical principles 37 agreeing with experience, there is no figure left for the orbit of the planet except a perfect ellipse.”
- 34. Galileo (1564-1642), Experimentalist Built his own telescope. Discovered four moons orbiting Jupiter. What does this suggest? Discovered sunspots. What might we infer about the Sun from these observations? Observed phases of Venus. Was imprisoned for the last 9 years of his life for his scientific discoveries.
- 35. Galileo Galilei • Turned a telescope toward the heavens • Made observations that: – contradicted the perfection of the heavens • Mountains, valleys, and craters on the Moon • Imperfections on the Sun (sunspots) – Supported the heliocentric universe • Moons of Jupiter • Phases of Venus – shows a full phase
- 36. • Galileo (1564-1642) first scientist to use a telescope to observe the sky. He observed the phases of Venus and the moons of Jupiter. Both observations supported the heliocentric model. 41
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- 38. Modern Universe • Is the Sun the center of the Universe? 43
Editor's Notes
- #10: At a certain point in an outer planet’s (Mars, Jupiter, Saturn) orbit, the planet’s motion against the starry background reversed, or went retrograde. Easily explained in the Copernican model as the Earth overtaking the other planet on its inside orbit, it was unexplainable on the geocentric model. Ptolemy’s brilliant solution was the introduction of epicycles. Ptolemy’s geocentric model was the standard cosmology for 1500 years. Will the Big Bang model be as robust? Contrary to legend, the Ptolemaic model did not get more complex and unwieldy, but because it did not model planetary motion exactly, its predictions became more and more inaccurate with time.