ASTR 101 Lecture 5 Outline of Last Lecture I The Scientific Thinking of Astronomy II Astronomical Observations Benefiting Ancient Societies III IV A Ancient civilizations achievements in astronomy Greek Roots Copernicus Tycho and Kepler A Kepler s three laws of planetary motion B How did Galileo solidify the Copernican revolution Outline of Current Lecture I Galileo Overcame Major Objections II Order of Astronomers and Their Contributions III Idealized Scientific Method Current Lecture Galileo 1564 1642 overcame major objections to the Copernican view Three key objectives rooted in the Aristotelian view were the following 1 Earth could not be moving because objects in air would be left behind 2 Noncircular orbits are not perfect as heavens should be 3 If Earth were really orbiting the sun we d detect stellar parallax Overcoming the first objection nature of motion Galileo s experiments showed that objects in air would stay with a moving earth o Aristotle thought that al objects naturally come to rest o Galileo showed that objects will stay in motion unless a force acts to slow the object down Overcoming the second objection heavenly perfect Tycho s observations of comet and supernova already challenged this idea Overcoming the third objection parallax Tycho thought he had measured stellar distances so lack of parallax seemed to rule out an orbiting Earth Galileo showed stars must be much farther then Tycho thought in part by using his telescope to see that the Milky Way is countless individual stars If stars were much farther away then lack of detectable parallax was no longer so troubling Galileo also saw four objects orbiting Jupiter proving that now all objects orbit the Earth Galileo s observations of phases of Venus proved that it orbits the Sun not the Earth In 1633 the Catholic Church ordered Galileo to recant this claim that the Earth orbits the sun His book on the subject was removed from the church s library and banned In order Plato 424 348 B C Aristotle 384 322 B C Aristarchus 260 B C solar centric parallax Ptolemy C A D 100 170 retrograde motion Copernicus 1473 1573 retrograde motion Tycho 1546 1601 data collection Kepler 1571 1630 ellipsoidal orbits Galileo 1564 1642 moving Earth non circular orbit parallax The first successful measurements of stellar parallax were made by Friedrich Bessel in 138 for the star 61 Cygni The parallax was 0 314 arcsec The nearest star to the Sun Proxima Centauri has a parallax of 0 7687 arcsec this angle is approximately that subtended by an object 2 centimeters in diameter located 5 3 kilometers away How can we distinguish science from non science Defining science can be surprisingly difficult Science comes from the Latin scientia meaning knowledge Idealized scientific method Based on proposing and testing hypothesis Hypothesis educated guess But science rarely proceeds in this way o Sometimes we start by just looking then trying to find explanations
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