Geocentric and Heliocentric Models of the Solar System

1. Study Points • Describe the geocentric and the heliocentric models of the solar system. • The word planet derives from the Greek "planetes" which means wanderer. Why were the planets called wanderers? • Explain Aristotle’s main argument against the heliocentric model. • What was Aristotle’s other (and weaker) argument against the heliocentric model? • Who gave the first evidence in favor of the heliocentric model? What was the evidence? • Who added the mathematical calculations to the geocentric model? • When a planet undergoes retrograde motion, what does it look like in the sky and what direction does the planet move day to day? • How did the geocentric model explain retrograde motion? • How did the heliocentric model explain retrograde motion?

2. Before the Copernican Revolution Part 1 of 2 Lectures on the Copernican Revolution

3. Before the Copernican Revolution – Greek Astronomy • Greeks (influenced by Babylonia, Mesopotamia, Egypt, Rome) • ~700 BC to ~140 AD • Some ideas and people • Know the starred* items

4. Two Different Solar System Models Everything orbits around what? Geocentric Model* - Earth-centered* (from Aristotle, 384-322BC) Earth Sun Heliocentric Model* - Sun-centered* (from Copernicus, 1473-1543AD)

5. Astronomy Before the Copernican Revolution • People all over the world tracked Sun, Moon, and stars to keep time and seasons quite accurately • Useful for planting & navigating • Many understood the Moon reflected sunlight • Few understood how objects really moved in space

6. Discuss • How do we know the Sun is at the center of our solar system? Can you think of ways to prove the Earth orbits around the Sun? • What is the evidence you could use to prove to a member of the “Flat Earth Society” that our planet is, indeed, round? • Attendance: Write down your full name and your best reason for the Earth being round.

7. Prior to the Copernican Revolution – Greek Astronomy Greeks ~500 BC • What is the sun? Fire? • Tiny lights in the sky? • Why do 7 lights wander among the others?* • 7 Planetes* = wanderers* • The 7 included: Sun, Moon, Mercury, Venus, Mars, Jupiter & Saturn • The 7 moved differently than the stars science.msfc.nasa.gov/ ssl/pad/solar/surface.htm imagine.gsfc.nasa.gov/.../ news/22apr02.html http://artsci.shu.edu/physics/1007/retro2.gif

8. Prior to the Copernican Revolution – Greek Astronomy Pythagoras of Samos ~500 BC • Earth is a sphere • Sphere is perfection in math • Crystal spheres for 7 planetes: Sun, Moon, 5 planets • Already thinking geocentric http://library.thinkquest.org/C0126626/fate/geocentric.jpg

9. Prior to the Copernican Revolution – Greek Astronomy Plato ~360 BC • Heavens are perfect, unchanging (from mathematical perfection) • Heavenly motion must be in circles and uniform • starting with simplest first

10. Prior to the Copernican Revolution – Greek Astronomy Aristotle ~350 BC • Plato’s student • Earth: corrupt, changeable, imperfect • Separation of perfect heavens and Earth • Arguments for geocentric model* • No parallax of stars** (main argument) • Should see parallax with heliocentric (we do now) • Moon would be left behind if Sun-centered* • Parallax is the apparent change in position of an object due to the change in position of the object or the observer • Parallax thumb demonstration

11. Prior to the Copernican Revolution – Greek Astronomy Aristarchus ~300 BC • First evidence for Heliocentric solar system model • Measured size of Sun based on the Sun being much larger than Earth* • Measured Sun was much farther away than Moon • Eratosthenes, northern Africa, measured size of Earth ~240 BC

12. Prior to the Copernican Revolution – Greek Astronomy Ptolemy ~140 AD • Geocentric model* (often called the Ptolemaic system) • Mathematical model of universe* • Perfect Bodies and orbits: circles, spheres • Uniform motion • Epicycles explain retrograde motion* • Forward motion on half of epicycle*; Backward motion on other half*

13. From Cycles of the Sky & Moon Lectures Already know this: • Minute to Minute: the Sun, Moon, stars, planets appear to rise in • Day to Day: Moon moves • New information: • Day to Day: Planetstypicallymove • Retrograde Day to Day Motion: Planets move

14. From Cycles of the Sky & Moon Lectures Already know this: • Minute to Minute: the Sun, Moon, stars, planets appear to rise in East and set in West due to Earth’s spin (rotation). (East to West) • Day to Day: Moon moves West to East due to Moon’s orbit (revolution) around Earth. New information: • Day to Day: Planetstypicallymove West to East due to their orbits around the Sun. (similar to Moon) • Retrograde Day to Day Motion: Planets move East to Westdue to their orbits around the Sun and the difference in speeds of Earth and other planet.

15. Retrograde Motion (Day to Day) Sometimes planets moved backwards against the background of stars. Retrograde motion is East to West and observed day to day. Minute to minute motion across sky is still East to West due to Earth’s rotation.

16. Ptolemy • Geocentric Model • Perfect circles, spheres, uniform motion • Added epicycles to explain retrograde motion* Mars’ Epicycle Earth Mars

17. Both models explain observations… Copernican Revolution Retrograde motion of planets

18. Retrograde motion – Geocentric Explanation • Planets ride on epicycles • Sometimes appear to • move backwards Prior to the Copernican Revolution – Greek Astronomy

19. Retrograde motion – Heliocentric Explanation • One planet overtakes • another planet. • Slower planet appears to • move backwards. • Retrograde motion is due • to a difference in speeds of the planets.* Copernican Revolution

20. Retrograde motion – Heliocentric New (and correct) explanation of retrograde motion of the planets: due to speed difference* • Retrograde (westward) motion of a planet occurs when the Earth passes the planet. • Ptolemy’s epicylces unnecessary Copernican Revolution

21. Retrograde Motion of Mars Copernican Revolution https://upload.wikimedia.org/wikipedia/commons/7/70/Apparent_retrograde_motion_of_Mars_in_2003.gif

22. Retrograde Motion of Mars Copernican Revolution Watch: https://www.youtube.com/watch?v=2lDcBwkeeuU

23. Big Gap Before Copernican Revolution Prior to the Copernican Revolution • Dark Ages in Europe, ~400-1400 AD • Roman libraries sacked, famine, wars, & plague • Europe sees very little progress • Islamic Golden Age of Science, ~500-1200 AD Long time between Ptolemy ~140 AD to Copernicus ~1500 AD

24. Big Gap Before Copernican Revolution Prior to the Copernican Revolution • Dark Ages in Europe, ~400-1400 AD • Islamic Golden Age of Science, ~500-1200 AD • Al Mamon starts Baghdad school of astronomy ~800AD • Islamic astronomers criticized & improved Ptolemy’s model • Native Americans & Chinese document supernova in Taurus constellation, now Crab Nebula, 1054 AD • Observatories built in Asia, Middle East, & northern Africa Long time from Ptolemy ~140 AD to Copernicus ~1500 AD

25. Summary • Before Copernicus ~700BC to 140 AD • Geocentric Model Dominated • Pythagoras of Samos • Plato • Aristotle* • Aristarchus* • Ptolemy*

26. Planetarium Observation • Planetarium Start Sep. 12; Due Dec. 3 (10 points) Go to a planetarium show • Best Option: Bell Planetarium Class Field Trip on Thursday, October 3. (FREE!) • Bus from Minneapolis College at 8:30am from the corner of Spruce Place & Harmon Place on the south side of Science bldg., by T bldg. Bus returns by 10:45am. • Free show at 9:15am this day only. Parking is $5 if driving separately. Bell Museum address and directions. • If you do not go to the Bell Planetarium with the class, then you can go any time on your own at your own cost. See the link at the top for options: • Como Planetarium Tuesdays at 7pm • Bell Museum throughout the week • Jackson Middle School classroom planetarium • Make a Shoebox Planetarium You only need to do this once. If you go to the Bell on Oct. 3, then there is no need to do any more for this.

27. Observation Projects OBSERVATION PROJECTS: (in order of due date) 130 points as options. Maximum cannot exceed 100 points. • Earth-Sun Scale ModelDue Sep. 10 (10 points) Make scaled model & take picture  • Sunset – Part 1 Due Oct. 1 (10 points) Take picture of sunset about 7pm • Moon Phases Due Oct. 8 (10 points) Observe 4 phases & record in table • Planetarium Due Dec. 3 (10 points) Go to a planetarium show • Telescope Due Dec. 17 (20 points) Look through a telescope • Stargazing Due Dec. 17 (20 points) Go stargazing & write report • Moon Craters Due Dec. 17 (10 points) Look at magnified moon craters FUTURE: (don’t start yet) • Astrophysics Lecture Due Dec. 3 (10 points) Attend 1 U of M lecture on Oct. 10 or write report • Astronomy News Report Due Dec. 10 (20 points) Write astronomy news report • Sunset – Part 2 Due Dec. 10 (10 points) Take 2nd picture of sunset in same location

28. Homework • Continue flashcards of STUDY POINTS • Do D2L Brightspace Quizzes 1 – 3 (new quiz today) • Work on Observations • Come prepared to Lab – Star Charts Lab • If you missed lab Tuesday, come talk to Raquel • Lab next week – watch email for Safe Sun Lab – probably Tuesday, 9/17 – get notebook ready • This will only happen on 1 day and all lab students need to come that day. There will be no lecture on this day. • Test 1 Tuesday, Sep. 24 • To prepare: study points & 4 D2L Brightspace quizzes • About 60 multiple choice questions. Bring a pencil. • Optional – bring calculator (not graphing), some in the room to use • Grades updated weekly