1. Bellwork 1.Who is credited with the revolutionary model of a HELIOCENTRIC solar system? A. Aristotle B. Ptolemy C. Galileo D. Copernicus 2.The planets loop backwards in their orbits. A.TRUE B.FALSE 3.During which months is Earth closest to the Sun? 1

2. The story so far…. Ancient Greeks had a GEOCENTRIC model of the solar system with Earth in center and Sun and planets in perfect circles. Ptolemy add many epicycles to explain the looping of planets during retrograde motion. Galileo used a telescope to see phases of Venus, Jupiter’s moons, rotating sunspots Copernicus made a HELIOCENTRIC model of the solar system with the Sun in the center so the planets were NOT looping backwards, Earth’s faster orbit was ‘passing’ the slower outer planets. 2

3. http://www.classzone.com/books/earth_science/terc/content/investigations/es2603/es2603page01.cfm 3

4. Kepler’s Model of the Solar System 4

5. Tycho Brahe (1575) After seeing the total eclipse on August 21, 1560, and became a master of careful astronomical OBSERVATIONS. Lost part of his nose in a duel and replaced it with a metal one. Made DETAILED naked eye observations of the motions of the planets. In the course of 30 years, he had amassed the most accurate astronomical DATA of the day 5

6. Mathmatician - Kelper's mathematical skills were extraordinary. He could not get Tycho's very careful observations to fit Copernicus’ model. He constructed 3 Laws about planets orbits: SHAPE, SPEED, TIME Kepler ‘inherited’ the observations after the sudden death of Tycho Johannes Kepler’s Johannes Kepler’s (1600) 6

7. Kepler’s 3 Laws of Planetary Motion 1 st Law: Ellipses! The SHAPE of the orbital paths of each planet is an ellipse (NOT a perfect circle) (with the Sun not exactly in the center, but at one focus) 7

8. http://highered.mcgraw- hill.com/olcweb/cgi/pluginpop.cgi?it=swf::800::600::/sites/dl/free/007299181x/787 78/Kepler_Nav.swf::Keplers%20Second%20Law%20Interactive 8

9. 2 nd Law: SPEED of the planet An imaginary line connecting the Sun to any planet sweeps out equal areas in equal time. Area 2 Area 1 90 days Planets have variations in their orbital speed 9

10. Kepler’s 3 rd Law: a planet’s orbital TIME is proportional to its distance. P 2 (years) = A 3 (AU) 1 Astronomical Unit = The Earth-Sun Distance (93 million miles) In other words……the farther away the planet, the longer its ‘year’ 10

11. Kepler’s Third Law Object a (AU) P (year) a3a3a3a3 P2P2P2P2 Mercury0.3870.2410.0580.058 Venus0.7230.6150.3780.378 Earth1.001.001.001.00 Mars1.521.883.513.53 Jupiter5.2011.9141.142. Saturn9.5429.5868.870. Uranus19.284.07,080.7,060. Neptune30.1165.27,300. 27,200. 27,200. Pluto39.5248.61,600. 61,500. 61,500. = = = = = = = = = 11

12. 12 Heliocentric Solar System Using data construct a model to show the correct SIZE and SCALE

13. Isaac Newton (1642 – 1727) One of the most brilliant theoreticians to ever live. One of the most brilliant theoreticians to ever live. Explained WHY the planets move as they do. Explained WHY the planets move as they do. He formulated three laws of motion and the law of universal gravitation. He formulated three laws of motion and the law of universal gravitation. 13

14. Newton’s 1 st Law of Inertia: Objects in uniform straight line motion continue in straight line motion unless an outside force is applied to change their motion Once in orbit, a planet will continue its orbital motion at constant velocity until an outside force (asteroid, another planet?) acts on it to change its orbit. 14

15. Newton’s Second Law The ACCELERATION (change in motion) of an object is directly proportional to the net FORCE acting on the object, is in the direction of the net force, and is inversely proportional to the MASS of the object. a = F net mass OR F = ma WHY 15

16. Newton’s Third Law Whenever one object exerts a force on a second object, the second object exerts an equal and opposite force on the first object. “To every action there is an equal and opposite re-action.” Forces are interacting in PAIRS – one object on another 16

17. Law of Universal Gravitation Mass attracts mass Gravity is the FORCE that causes objects to move ! 17