Juno s Voyage to Jupiter Orbital Motion of Galilean Moons Movie captured by Juno First movie of orbital motion in history Image Credit Michael Steginia Adam Block NOAO AURA NSF Course Announcements Quiz 1 TODAY Given at end of class Friday 2 Sept class cancelled Extra Credit Sessions have begun Next opportunity is next week Be sure to sign up if you want to attend Sign up sheets outside of Room 108 in Nielsen Physics and Astronomy Assignments Reading Assignments Chapter 2 Sections 2 5 2 8 Including More Precisely 2 1 Read by Wednesday 7 Sept Parallel Lectures No new episodes Mastering Astronomy Chapter 1 Homework Due Wednesday 31 Aug at 11 59 PM EDT The Copernican Revolution BEGIN CHAPTER 2 Brief Introduction to Chapter 2 Understanding Planetary Motions Chapter 1 covered the general motions of the Sun Moon and stars in the sky due to Earth s motions rotation revolution and precession and the motions of the Moon Chapter 2 focuses on understanding the motion of the planets wanderers in the sky and the physics behind orbital motions How to the planets move in the sky as viewed from Earth How do the planets move in general orbital motion A triumph of the scientific method to come to understand the physics of the heavens Historical Sections of Chapter 2 2 1 2 4 Left mostly for your reading Material Dr Lindsay wants you to know The Geocentric Ptolemaic Model Difference between geocentric and heliocentric models Who the following people are no need to memorize dates and how they contributed to the rise and acceptance of heliocentrism Nicolai Copernicus Pushed heliocentric model to explain retrograde motion of planets Tycho Brahe Made the most detailed observations of planetary positions i e generated the necessary data set This guy is a nut I highly encourage researching him Johannes Kepler Used Brahe s data to deduce the nature of planetary orbits Elliptical NOT Circular Galileo Galilei Made four fundamental that means you should know what they are telescopic observations demonstrating the validity of heliocentrism and the death of holding onto Aristotelian ideals Historical Sections of Chapter 2 2 1 2 4 Left mostly for your reading Material Dr Lindsay wants you to know The four telescopic observations Galileo made that provided the evidence needed to overturn the most powerful geocentric model called the Ptolemaic model Planetary Motions in the Sky The wanderers of the night sky Credit Yuri Beletsky Planetary Motions in the Sky Our idea of how Solar System is structured and what physical processes govern planetary motion must include Wandering nature of planets Planets always appear close to the Ecliptic Unlike the stars planets change position relatively quickly no fixed RA and Dec Planets appear to move at different speeds at different times Planets move west to east with respect to fixed star background prograde motion Mercury and Venus tethered to the Sun Mars Jupiter and Saturn exhibit retrograde motion east to west and appear brighter during this period The Solar System Two Concepts Prograde and retrograde motion using heliocentric model Geocentric model Heliocentric model Deferents Earth Sun Epicycle East Venus Sun Both constructions are flat which keeps all the planets near the Ecliptic Mars Earth Venus West Mars Orbits Mars s orbit is larger Superior Planet Venus s orbit is smaller Inferior Planet What structure of the Solar System explains all of these apparently complex motions Option One Geocentric Solar System Earth standing still at the center and everything moving around it This one that feels right as a person standing on the Earth Option Two Heliocentric Solar System Sun at the center of the Solar System and everything orbiting it Less intuitive and requires us to be much more clever to realize it is the right structure Planetary Alignments Oppositions Opposite Conjunctions Conjoined Sun Earth and planets in a line Opposition occurs at a planets closest approach to Earth Earth between planet and Sun only for Superior planets Conjunction occurs when a planet appears close to the Sun in our sky Inferior and Superior planets Inferior planet orbit as seen from Earth Planetary motions in the Sky Prograde and Retrograde Motion West During retrograde motion planets are at their brightest why East Prograde motion is night to night eastward motion Retrograde motion is night to night westward motion Planetary Motion in the Sky Prograde and retrograde motion using heliocentric model Prograde motion is nightto night eastward motion Retrograde motion is night to night westward motion To understand why these are the motions we observe from Earth we need to consider where the planets are over several months Orbital Period of Earth 1 year 365 25 days Orbital Period of Mars 684 5 days Being further away Mars orbits slower than Earth Orbits Earth Sun Mars Planetary Motion in the Sky Prograde and retrograde motion using heliocentric model Imagine our view of Mars Point 1 Time 0 months 1 1 Fixed Background Stars Planetary Motion in the Sky Prograde and retrograde motion using heliocentric model 1 1 2 PROGRADE More Eastward Imagine our view of Mars Point 1 Time 1 month 2 2 Fixed Background Stars Planetary Motion in the Sky Prograde and retrograde motion using heliocentric model 1 Imagine our view of Mars Point 1 Time 2 months 2 3 PROGRADE More Eastward 2 3 Fixed Background Stars 3 Planetary Motion in the Sky Prograde and retrograde motion using heliocentric model 1 Imagine our view of Mars Point 1 Time 3 months 3 4 RETROGRADE More Westward 2 4 3 Fixed Background Stars 4 Planetary Motion in the Sky Prograde and retrograde motion using heliocentric model 1 Imagine our view of Mars Point 1 Time 4 months 4 5 RETROGRADE More Westward 2 5 4 3 Fixed Background Stars 5 Planetary Motion in the Sky Prograde and retrograde motion using heliocentric model 1 1 2 PROGRADE More Eastward Imagine our view of Mars Point 1 Time 5 months 2 5 4 3 6 Fixed Background Stars 6 Planetary Motion in the Sky Prograde and retrograde motion using heliocentric model 1 6 7 PROGRADE More Eastward Imagine our view of Mars Point 1 Time 6 months 2 5 4 3 6 7 7 Fixed Background Stars Planetary Motion in the Sky Prograde and retrograde motion using heliocentric model Summary Retrograde motion for superior planets is caused by the Earth orbiting faster catching up to and passing the outer planet at opposition the outer planet and then racing away again 1 1 2 2 5 4 3 6 3 4 5 6 7 7 Fixed Background Stars Why brighter during
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