Gravitation and the Motions of the Planets

1. Gravitation and the Motions of the Planets

2. The Greeks Aristotle (350 B. C.) - GeocentricCosmology Aristarchus (300 B.C.) - Heliocentric Cosmology, the scale of the Solar system Eratosthenes (200 B.C.) - the size of the Earth to within 5%

3. Retrograde Motion of the Planets

4. Ecliptic

5. Ptolemy (100 AD) - Epicycles and Deferents

8. Ptolemy

9. Nicolaus Copernicus (1473 - 1543) • - Heliocentric Cosmology • The Sun is the center of the planets’ motions • The planets’ orbits are circles • The planets orbit the Sun with the closer ones moving faster than the farther

10. The order of the planets from closest to farthest from the Sun: • Mercury, Venus, Earth, Mars, Jupiter, Saturn • The stars are very far away compared to the planets.

12. The real explanation for retrograde motion

14. Tycho Brahe (1546- 1601) - Greatest observer of the pre-telescopic era (observational precision of 1 arcminute) - disproved the theory of the crystal spheres - discovered a new star (supernova)

17. Tycho Brahe (1546- 1601) - Greatest observer of the pre-telescopic era (observational precision of 1 arcminute) - disproved the theory of the crystal spheres - discovered a new star (supernova) - did not believe in Copernicus’ heliocentric model

18. Parallax

21. Johannes Kepler (1571 - 1630) Kepler’s Laws of Planetary Motion (1609 -1619)

23. Kepler’s First Law: The planets’ orbits are ellipses with the Sun at one focus.

24. The First Law Semi-major axis, a Foci

25. Kepler’s Second Law: The planets in their orbits sweep out equal areas in equal time intervals

26. The Second Law 1 4 3 2

27. The Third Law: P2=a3Where P = orbital period in yearsand a= semi-major axis in AU’s

28. The Third Law: P2=a3Where P = orbital period in yearsand a= semi-major axis in AU’sP (yrs) A (AU’s)Earth 1 1Jupiter 11.8 5.2Pluto 248 39.5

29. The Scientific Method

30. 1. Make an observation

31. 2. Form a hypothesis

32. Hypothesis – A tentative explanation Theory – A well-substantiated and tested hypothesis that has gained acceptance from the Scientific Community Law – A descriptive generalization about a behavior of the natural world, that has never been observed to be violated.

33. 2. Form a hypothesis Hypothesis must be: - consistent with known physical laws - testable

34. 3. Test the hypothesis (make another observation) 4. Based on the results of the test, modify or discard the hypothesis

35. Galileo Galilei (1564 - 1642) • -First Astronomer to use a telescope (1610) • - Discovered: • the phases of Venus

36. Galileo’s original drawing of Venus

38. Galileo Galilei (1564 - 1642) • -First Astronomer to use a telescope (1610) • - Discovered: • the phases of Venus • the moons of Jupiter

40. Galileo Galilei (1564 - 1642) • -First Astronomer to use a telescope (1610) • - Discovered: • the phases of Venus • the moons of Jupiter • the rings of Saturn

42. Galileo Galilei (1564 - 1642) • -First Astronomer to use a telescope (1610) • - Discovered: • the phases of Venus • the moons of Jupiter • the rings of Saturn • mountains, craters on the moon • Milky Way is made of stars

43. Galileo Galilei (1564 - 1642) • -First Astronomer to use a telescope (1610) • - Discovered: • the phases of Venus • the moons of Jupiter • the rings of Saturn • mountains, craters on the moon • Milky Way is made of stars • Sunspots

44. - Brought before the Inquisition and forced to recant his anti-geocentric beliefs

45. Isaac Newton (1642 - 1727) Newton’s Laws of Motion and Gravitation

46. Newton’s First law: An object at rest or traveling in a straight line at a constant speed remains in that state unless acted upon by an outside force.

47. Newton’s Second Law: F = ma

48. Newton’s Second Law: F = ma Force acceleration mass change in velocity speed & direction

49. Newton’s Third Law: For every action (force) there is an equal and opposite reaction(force)

50. Newton’s Law of Gravity