Presentation on theme: "Birth of Modern Astronomy OR How Nerds Changed the World!!!"— Presentation transcript:
1 Birth of Modern Astronomy OR How Nerds Changed the World!!! The Motion of PlanetsBirth of Modern AstronomyORHow Nerds Changed the World!!!Theory?Hypothesis?Law?Scientific Method?
2 How is science done? Observations Experiments Explanations Repeat TheoriesLawsRepeat
3 Assumptions of Early Models Geocentric - Earth in the middleEverything orbits the EarthStars are located on the Celestial SphereEverything moves in uniform circular motions
4 The Greeks Anaximander Pythagoras Eudoxus Aristotle Apollonius Celestial sphere rotates around the earthPythagorasEarth is a sphereEudoxusPlanet motion accounted for by separate spheresAristotleComplete model of the universe (4 elements)Perfect heavensApolloniusepicycles
9 The problem of Retrograde Motion: Apollonius The motion of these spheres did not account for retrograde motion.Apollonius introduces ‘epicycles’Roughly meaning ‘cycles within’
10 What is an epicycle?EpicycleThe Center of of epicycle revolves around the earthThe planet spins along the epicycle at the same time.MarsEarthDeferent
11 Enter the Roman: Ptolemy Brought it all togetherAdded the equant to adjust the model to match observationsWrote “The Mathematical Compilation”Destruction of Library of Alexandria(Europe lost almost all it’s written knowledge)The Arab Scholars called it “Almagest” (“the greatest”)This is how they came to know it once the work returned to Europe.
16 Tycho Brahe (1546-1601) Comet – beyond the Moon Supernova – far away Naked eye observations of planetsAccuracy through repetitionBest observations of planetary positionsHired “nerd” to help calculate modelDied….
17 Three Laws of Planetary Motion Johannes Kepler ( )Worked for BraheTook data after his deathSpent years figuring out the motions of the planetsCame up with…Three Laws of Planetary Motion
18 1. Planets move in elliptical orbits with the Sun at one foci PerihelionAphelionFoci (sing. Focus)Average distance from the Sun = 1 Astronomical Unit (1 A.U.)
19 2. Planets move faster at perihelion than at aphelion. 1 Month1 Month
20 3. Period is related to average distance P = period of the orbita= average distanceP2 = k a3Longer orbits - greater average distanceNeed the value of k to use the formulak depends upon the situationCan be used for anything orbiting anything else
21 P2 = a3 Special version of Kepler’s third Law – If the object is orbiting the SunP – measured in years,a – measured in A. U., then….P2 = a3
22 Galileo Galilei (1564-1642) Knew of Copernicus’s & Kepler’s work Used a telescope to look at the skyWhat did he see?
23 The Moon was an imperfect object Venus has phases
24 Jupiter has objects around it Saturn is imperfectThe Sun is imperfect
25 Isaac Newton (1642-1727) The Three Laws of Motion The ultimate “nerd” Able to explain Kepler’s lawsHad to start with the basics -The Three Laws of Motion
26 1. Law of Inertia - Objects do whatever they are currently doing unless something messes around with them.
27 2. Force definedF=maF=forcem=massa=acceleration (change in motion)
28 3. For every action there is an equal and opposite reaction. The three laws of motion form the basis for the most important law of all (astronomically speaking)Newton’s Universal Law of Gravitation
29 F=force of gravityG=constantM1, M2 = massesR=distance from “centers”Gravity is the most important force in the Universe
30 Newton’s Revisions to Kepler’s Laws of Planetary Motion: Kepler’s 1st and 2nd Laws apply to all objects (not just planets)3rd Law rewritten:4π2 and G are just constant #s (they don’t change)M1 and M2 are any two celestial bodies (could be a planet and Sun)Importance: if you know period and average distance of a planet, you can find mass of Sun (2 x 1030 kg) or any planet!Mass of Sun is kgMass of Earth is kgMass of Mr. J is 100 kg! WOW!30
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