ASTR 151 1nd Edition Lecture 4 Outline of Last Lecture II Summary of Chapter 1 III Chapter 2 The Copernican Revolution 2 1 to 2 4 Outline of Current Lecture IV Review on concepts in Chapter 1 V Tycho Brahe VI Johannes Kepler VII 2 5 The Laws of Planetary Motion VIII 2 6 Intro to the Dimensions of the Solar System Current Lecture II Concepts in Chapter 1 a When a parallax angle of a star is measured to be 0 002 the distance to the star is what i Distance 1 parallax ii Parallax is measured in arc seconds iii Distance is measured in parsecs iv Parallax 57 3 degrees Baseline Distance v 0 002 5 56e 7 degrees vi Distance 1 34e12 km 0 14 light years b Mars Jupiter and Saturn show retrograde motion because the earth moves faster in it s orbit c Copernicus important contribution to astronomy was the heliocentric model III Tycho Brahe a Last great naked eye astronomer b Made great number of precise measurements i Stellar novae or new stars didn t exhibit parallax lacked the parallax expected in sub lunar phenomena ii Comets aren t atmospheric phenomena iii Atmospheric tailless comets aren t as previously believed c Came up with Tychonic system a merge between Ptolemic and Copernican models i He made a model where the Earth did not move however all the other planets revolved around the Sun ii His model widely failed to the public These notes represent a detailed interpretation of the professor s lecture GradeBuddy is best used as a supplement to your own notes not as a substitute IV Johannes Kepler a As a kid he saw a comet and a lunar eclipse b Was a vital proponent to the heliocentric model c Originally wanted to become a minister but chose to be a math and astronomy teacher in Graz once the job was offered d Assisted Tycho Brahe in Prague in various projects V 2 5 The Laws of Planetary Motion a Purpose to describe planetary motion i Planetary orbits are ellipses with the Sun in the center 1 Circle 1 foci coincide 2 Semi major axis a ii Imaginary line connecting Sun and planet sweeps out equal areas in equal times 1 When closer to the Sun you go faster in rotation iii Square of period of planet s orbital motion is proportional to cube of semi major axis 1 In other words p 2 a 3 constant VI 2 6 Dimensions of the Solar System a AU Astronomical Unit distance from Earth to the Sun b Ration of mean radius of Venus s orbit to that of Earth is very well known c Kepler s laws were derived empirically which means by observation
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