1. Modern Day Astronomers (sort of) The New Guys

2. The Astronomers Copernicus Galileo Tycho Brahe Johannes Kepler Sir Isaac Newton

3. Copernicus O Life: 1473-1543 O Theory: O Reintroduced the heliocentric model of the Universe Proof? The New Guys

4. Proof? O 7 points 1. Earth is not the center of everything 2. Earth is only the center of gravity and of the lunar orbit 3. All planets revolve around the Sun 4. The stars are much farther away than the Sun 5. Apparent motion we see in the stars is due to the movements of the Earth Proof Cont’dCopernicus

5. Proof? Cont’d O 7 points 6. The Sun’s daily and yearly motion are due to the Earth’s rotation and revolution around the Sun 7. The Sun-centered model provides a natural explanation for the retrograde motion of the planets, which is again caused by the movement of the Earth Copernicus

6. Galileo O Life: 1564 – 1642 O Contributions: O One of the first to turn a telescope to the heavens O First to see the moons of Jupiter O Recognized that his observations conflicted with Ptolemic views The New Guys Galileo’s Work Joke

7. Galileo’s Tracking of Jupiter's Moons Galileo

9. Tycho Brahe O Life: 1546-1601 O Known For: O Made the most extensive observations with just the naked eye. O He noticed errors in the Ptolemic planetary tables O Had his own semi- heliocentric theory of the solar system Man with the Golden Nose The New Guys Theory

10. Brahe

11. Johannes Kepler O Life: 1571 - 1630 O Known for: O Used Brahe’s observations to develop three laws of planetary motion = Kepler’s laws The New Guys 1 st Law 2 nd Law 3 rd Law

12. Kepler’s 1 st Law O Each planet moves in an ellipse with the Sun at one focus O An ellipse is an elongated circle- O with two foci -a point around which the planet revolves, O a line drawn through both foci and including the orbit is known as the major axis O ½ this distance is known as the semi-major axis (the average distance from the Sun) KeplerImageKepler’s 1 st Law cont’d

13. Kepler’s 1 st Law

14. Kepler’s 1 st Law O Eccentricity O is the ratio of the distance between the foci to the length of the major axis (or diameter) O A circle is an ellipse whose eccentricity is zero O Using the semi-major axis and the eccentricity: O Perihelion: closest point to the Sun O Aphelion -a planets farthest point from the Sun (ap- think away) KeplerImageCartoon

15. Kepler Kepler’s 1 st Law

16. Kepler

17. Kepler’s 2 nd Law O The line between the Sun and the planet sweeps out equal areas in equal time intervals O Planets move fastest when closest to the Sun ImageKepler

18. Kepler’s 2 nd Law

19. Kepler’s 3 rd Law O “Harmonic Law” O The time it takes for a planet to complete one period (a planetary year) is equal to the square root of the semi-major axis cubed O p 2 = a 3 Kepler

20. Newton O Kepler knew the how but not the why of planetary motion O It took Isaac Newton to explain why all objects interact the way that they do The New Guys Laws of MotionLaw of Gravity Planetary Motion Correcting Kepler

21. Newton Laws of Motion 1. A body at rest stays at rest unless acted upon by an outside force, a body in motion stays in motion unless acted upon by an outside force 2. Force is equal to mass times acceleration F = ma 3. For every action there is an equal and opposite reaction- this means that you attract the Earth with exactly the same force as it attracts you- also explains how a rocketship is propelled Newton

22. Newton’s Laws of Gravity O F = Gm 1 m 2 r 2 O F = force O G = constant 6.67 x 10 -11 Nm 2 /kg 2 O M 1 = mass of body #1 O M 2 = mass of body #2 O R = radius between two bodies O Force of gravity for Earth = 9.8 m/s 2 Newton

23. Planetary Motion O So why doesn’t Earth fall into the Sun? O A combination of gravitational forces of both bodies and our planet’s velocity Newton

24. Correcting Kepler’s Laws O The orbit of a planet around the Sun is an ellipse with the common center of mass of the planet and the Sun at one focus Newton