Chapter 1 History of Astronomy The Copernican Revolution

1. Chapter 1 History of Astronomy The Copernican Revolution Mars rover Spirit

2. The Motions of the Planets Sun, Moon, and stars all have simple movements in the sky, consistent with an earth-centered system • Planets: • move with respect to fixed stars • change in brightness • change speed • have retrograde motion

3. Ptolemy 2th century Geocentric Universe Fig. 5-10, p.81

4. Ptolemaic system to explain retrograde motion Fig. 5-11, p.81

5. Copernicus 1473 – 1543 Heliocentric Universe Believed all motions are perfect circles p.82

6. Retrograde motion of planets Heliocentric Model Apparent Motion Geocentric Model

7. Copernican model explaining retrograde motion Fig. 5-15, p.83

8. Tycho Brahe (1546 – 1601) observatory Fig. 5-16, p.84

9. Tycho Brahe 1546-1601 Johannes Kepler 1571-1630 p.86

10. Orbits are ellipses. Sun at a focus point. Eccentricity is 0 for circle and 1 straight line. The closer the number to 1 the flatter the ellipse. Equal areas swept in equal time. a³ = p². a in AU and p in years. Kepler Three Laws

11. Ellipse Eccentricity (e) = distance between foci / major axis є between 0 and 1. Circle e = 0. Almost a line e ~ 1. Fig. 5-18, p.85

12. Kepler’s laws 1. Planetary orbits are ellipses, Sun at one focus

13. Kepler Second Law a Area B Area A b Area A and B are equal and swept in equal time. Planet has to move faster in a than b. Fig. 5-19, p.86

14. Kepler 3rd law a³ = p² Fig. 5-21, p.87

15. The Birth of Modern Astronomy Kepler’s laws 3. Square of period of planet’s orbital motion is proportional to cube of semi major axis

16. Galileo Galilei 1564-1642 Father of Modern Astronomy First person to use telescope to observe the sky. 1. Craters and mountains on the Moon. 2. Jupiter has 4 moons. 3. Sun spots. Sun is not perfect. Next page. 4. Phases of Venus. (P. 18) Agrees with Sun centered universe. p.89

17. Ptolemaic model Phases of Venus as observed by Galileo match lower one. Copernican model

18. Sunspots as recorded by Galileo Fig. 5-26, p.90

19. Isaac Newton 1642-1727 F = ma F = -GmM/r² Force of gravity p.91

20. Newton’s Laws Kepler’s lawsare a consequence ofNewton’s laws. m1a1 = m2a2

21. The Solar System, all planets almost in the same plane and revolve around Sun in same direction. Fig. 5-29, p.94

22. Is Pluto a planet – (Yes until Aug 2006).Now dwarf planet (Maybe, change possible in 2009). Are there other planet type objects? YES called Kuiper Belt Objects. OTHER PLANETS (KBO’s)

23. The Dimensions of the Solar System The distance from the Earth to the Sun is called an astronomical unit. Its actual length may be measured by bouncing a radar signal off Venus and measuring the transit time.

24. Newton’s Laws Gravity On the Earth’s surface, theaccelerationdue to gravity is approximately constant, and directed toward the center of the Earth:

25. Gravity Leaning tower of Pisa experiment By Galileo Galilee

26. Newton’s Laws Gravity For two massive objects, thegravitational forceis proportional to the product of their masses divided by the square of the distance between them: Weight = Mass × Gravity (acceleration) On the Moon gravity strength is 1/6. A weight of 120 lb on Earth will be only 20 lb on the Moon.

27. Newton’s Laws Gravity The gravitational pull of the Sun keeps the planets moving in their orbits.

28. Newton’s Laws Massive objects actually orbit around their common center of mass; if one object is much more massive than the other, the center of mass is not far from the center of the more massive object. For objects more equal in mass, the center of mass is between the two. m1 m2 a1 a2 m1a1 = m2a2