ASTR 101 Lecture 5 Outline of Last Lecture I. The Scientific Thinking of AstronomyII. Astronomical Observations Benefiting Ancient SocietiesA. Ancient civilizations’ achievements in astronomyIII. Greek RootsIV. Copernicus, Tycho, and KeplerA. Kepler’s three laws of planetary motionB. How did Galileo solidify the Copernican revolutionOutline of Current Lecture I. Galileo Overcame Major ObjectionsII. Order of Astronomers and Their ContributionsIII. Idealized Scientific MethodCurrent LectureGalileo (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 parallaxOvercoming 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 resto 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
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