PHY 102 1st Edition Outline of Last Lecture I Yearly Solar Motions a Position of the sun in the sky b North to South motion of the sun II General Planetary Motion a Inferior Planets b Superior Planets III Zodiac IV Theories of Heliocentrism and others a Philolaus Cosmology b Earthshine c Homocentric Spheres of Eudoxus d Unacceptance Outline of Current Lecture I Eratosthenes and the Size of the Earth II Geocentrism a Eudoxus b Appoloneus c Ptolemaic System III Copernicus Brahe Kepler 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 a Copernicus b Brahe c Kepler i Elliptical Motion ii Equal Areas iii Period 2 Distance 2 Current Lecture I Eratosthenes and the Size of the Earth a How could Earth move given its great size i In early days rest was considered the natural state ii Angels were believed to move the celestial beings iii Shows that evidence can be suspect b Eratosthenes 200 B C i Traveler and scientist ii In a well in Syene on the first day of summer sun was right overhead 1 year later goes to a well in Alexandria and sees the sun was at a different angle iii Equation he used angle between the two cities 360 degrees known distance between the two cities Circumference of the earth iv Evidence based on logic and reasoning leads to knowledge II Geocentrism a Homocentric spheres of Eudoxus i Homocentric spheres did not account for planets appearing brighter opposite the sun superior planets get brighter when opposite the sun ii Homocentric spheres did not accurately predict motion of the planets b Example headlights get closer lights appear brighter c Retrograde loops d Appolonius introduces epicycles i Deferent a point about which a planet moves ii Epicycle planet moves around a deferent and epicycle moves around the earth iii Says when the planet retrogrades that it is brightest because it is closer to the earth iv Doesn t account for irregularity Deferent Mars E e Ptolemaic System i Extension of Appollonius s deferent and epicycle 1 Accepts and utilizes circular planetary motion ii Summer is 92 days long iii Winter is 89 days long Sun appears to travel through these 90 degree section equally quickly E III Copernicus Brahe a Nicholas Copernicus i 19 Feb 1473 24 May 1543 ii Ptolemaic system is inaccurate and overly complex iii Simpler sun centered system that includes perfect circular motion iv Retains tiny epicycles v Mars is moving more slowly so as we view Mars its position changes among the background stars vi Accounts for retrograde motion vii Year earth s revolution viii Day earth s rotation ix Month moon s revolution x Copernican system is more simple less circles b Tycho Brahe Tychonic System i 14 Dec 1546 24 Oct 1601 ii Cannot accept Earth s motion iii Sun orbits earth planets orbit sun Planets Moon Mars Earth Sun E iv Sky made of quintessant essence not of the earth s materials c Johannes Kepler i Rejects perfect circular motion studying Mars ii Hven worked there with an assistant most meticulous of all observers of astronomy iii Discovered 3 law 1 Elliptical motion a Measured the angular distance between the earth and mars after 687 days 1 mars year b Different at different times means it s an ellipse 2 Equal areas a As a planet gets closer to the sun it speeds up as it gets farther it slows down b Sumer is 93 days because we are farthest from the sun 3 Period 2 Distance 3 iv System used today