Lecture 5

1. Lecture 5 ASTR 111 – Section 002

2. Outline • Quiz Discussion • The Moon in its orbit review • Gravitation and the Waltz of the Planets – through section 4.3 of text.

3. The great debate • Geocentric – Earth is fixed and everything rotates around it. • Heliocentric – The sun is fixed and everything rotates around it. The resolution of this question is one of the great examples of the scientific method

4. The great debate • Geocentric – Earth is fixed and everything rotates around it. • Heliocentric – The sun is fixed and everything rotates around it. The resolution of this question is one of the great examples of the scientific method

5. http://www.youtube.com/watch?v=FHSWVLwbbNw&feature=related

6. Parallax • Apparent change in an objects position due to a change in the line of sight • In astronomy we use Apparent and Actual in many contexts. Parallax is one example.

7. Side note: What is wrong with this picture (from text)?

8. Side note: What is wrong with this picture (from text)? 14 hours

9. What if the nearby object is moving too? • That is, moving at a speed comparable to the speed of Earth in its orbit?

10. Typical observations • http://www.youtube.com/watch?v=cSU5VwIQTNI

11. Typical observations Notice that reference point is the background stars.

12. Mercury in retrograde • This happens three to four times per year, when the planet Mercury slows down, and appears to stop (station) and move backward (retrograde). It's an optical illusion, since there is forward movement, like speeding by a slow-moving train -- as it recedes, it appears to go backward. http://www.astrologycom.com/mercret.html#TOP

13. Mars goes retrograde later in the week (Exact on the 15th, 3:24 am EST), but many are already sensing a cosmic winding down. Mars is in the water sign Cancer, an intiating cardinal sign, but one that takes stealthy sidesteps forward, feeling out every situation. In retrograde, Mars stews in his emotional juices, so to speak, and it may be harder to get things done. Some might experience less energy, quick tempers, irrational arguments and defensive overreacting. Mars here amplifies Cancer's protective instinct, which brings out both compassion for all of humanity, and its shadowy twin, clannish "us against them" rationales. It's a chance to integrate feeling into actions, and possibly a series of lessons in anger management. http://astrology.about.com/b/2007/11/12/mars-retrograde.htm

14. Projection (in context of celestial sphere) • Connect point on celestial sphere with a line to the center of Earth. Where line intersects Earth’s surface is where celestial point projects onto Earth’s surface. • Need two points + a projection point

15. Understanding Retrograde Motion

16. P U U always connects line from eye through P and beyond Top View

17. If U is fixed and P rotates CCW, what does U see on the wall? • Beam traces a line from left to right • Beam does not move • Beam traces a line from right to left

18. If U is fixed and P rotates CCW, what does U see on the wall? • Beam traces a line from left to right • Beam does not move • Beam traces a line from right to left

19. P U U always connects line from eye through P and beyond Top View

20. P U U always connects line from eye through P and beyond Top View

21. Will U ever see P reverse directions with respect to the distance stars? • Yes • No

22. Will U ever see P reverse directions with respect to the distance stars? • Yes • No

23. Now move U away from center

24. P U Top View

25. If U is fixed and P rotates 90o CCW, what does U see on the wall? • Beam traces a line from left to right • Beam does not move • Beam traces a line from right to left

26. If U is fixed and P rotates 90o CCW, what does U see on the wall? • Beam traces a line from left to right • Beam does not move • Beam traces a line from right to left

27. P U Top View

28. P U Top View

30. P U Top View

31. If P is fixed and U rotates 90o CCW, what does U see on the wall? • Beam traces a line from left to right • Beam does not move • Beam traces a line from right to left

32. If P is fixed and U rotates 90o CCW, what does U see on the wall? • Beam traces a line from left to right • Beam does not move • Beam traces a line from right to left

33. P U Top View

34. P U Top View

40. Distant “stars” 4 5 3 2 6 1 7 8 9

41. In this diagram, are the Republicans to the East or West? • At points 1-8, an observer on Earth will see the planet in front of a different “star”. Label them below: • Rush Limbaugh • During which intervals was the planet moving “to the right” and which “to the left”? When was the planet in retrograde motion?

42. Distant “stars” 4 5 3 2 6 1 7 8 9

43. Typical observations

45. 4-5-6 = retrograde motion (westward against background stars) 1-2-3-4 and 6-7=8-9 = protograde (direct) motion (eastward against background stars)

46. Occam’s Razor

47. Occam’s Razor • Law of parsimony • When all things are equal, choose the theory or model that is simpler or requires fewer assumptions

48. As a group, write down two theories for a given phenomena. One theory should not be parsimonious.

49. Copernicus devised the first comprehensive heliocentric model • Copernicus’s heliocentric (Sun-centered) theory simplified the general explanation of planetary motions • In a heliocentric system, the Earth is one of the planets orbiting the Sun • The sidereal period of a planet, its true orbital period, is measured with respect to the stars

50. Copernicus devised the first comprehensive heliocentric model • Some planets always observed near Sun while looking in the sky. • Some planets are sometimes observed at night and sometimes opposite the Sun.