1. A brief History of Astronomy

2. How is science done? Observations Experiments Explanations Theories Laws Repeat

3. Assumptions of Early Models Geocentric = Earth in the center of the universe Everything orbits the Earth Stars are located on the Celestial Sphere Everything moves in uniform circular motions

4. Thales (624-546BCE) Philosopher (“tails”) Proposed the first model of the universe that did not rely on supernatural forces Simple model: –Small, flat Earth surrounded by a sheet of water, with a single vast sphere. –This sphere carried the stars

5. Pythagoras (580-500BCE) Proposed a more complex model of the universe –the Earth was a sphere –All stars and planets were on their own concentric spheres beyond the Earth

7. Plato (427-347BCE) Proposed that celestial bodies (planets, etc) moved about Earth at a constant speed, and followed a circular motion with Earth at the centre. Asserted that heavenly motion must be in perfect circles and that heavenly objects reside on perfect spheres

9. Aristotle

10. Problems with Aristotle Retrograde motion… it didn’t make sense with the current model

11. Key Terms Retrograde motion= motion that is backward compared to the norm. Example: Mars travels in apparent retrograde motion when it moves westward rather than the more common eastward.

12. Ptomely (100-170 BCE) Argued that each planet also revolved in a small circle (EPICYCLE) His GEOCENTRIC model (the Ptolemaic model) remained for 1400 years

13. Key Terms Epicycle= a small rotation on which a planet is placed. The epicycle then moves on a larger orbit. Used to explain retrograde motion.

14. Ptolemaic Model

15. http://faculty.fullerton.edu/cmcconnell/Planets.html#2

16. THE COPERNICAN REVOLUTION

17. The Greeks and other ancient peoples developed many important ideas of science What we now consider science arose during the European Renaissance (14 th to 16 th century) The dramatic change now known as the Copernican revolution spurred the development of virtually all modern science and technology

18. Nicholaus Copernicus (1473- 1543) Proposed a sun-centered (HELIOCENTRIC) universe where the Earth travelled around the Sun. Held onto the idea of epicycles and constant circular motion Proposed that stars were very far away Proposed that the Earth rotated on an axis

20. http://faculty.fullerton.edu/cmcconnell/Planets.html#2

21. Feared criticism from the Catholic Church. Early supporters were drawn to the aesthetic advantage of his model. Belief in circular orbits made it no less complex than the Ptolemaic As a result it won few converts for 50 years

22. Why was is it considered such a big deal?

23. It was a strange and even rebellious notion It was a time of major upheaval: Columbus had sailed to “the New World”, Martin Luther has proposed radical revisions in Christianity The present PARADIGM (or prevailing scientific theory) is a way of seeing the universe around us. Questions, research and interpretation of results is all in the context of this theory. Viewing the universe in any other way requires a complete shift in thinking.

24. Replacing a theory that had been believed to be correct for nearly 2000 years is not easy Only when the old theory’s complexity made it beyond usefulness was the intellectual environment at a point that the concept of heliocentric universe was possible

25. By his time, tables of planetary motion based on the Ptolemaic model were noticeably inaccurate. But few people were willing to undertake the difficult calculations required to revise the tables. He was probably motivated in large part by the much simpler explanation of retrograde motion offered by a Sun- centered system.

26. Tycho Brahe (1546-1601) Considered the best naked-eye observer of all time. Observed a supernova and a comet Was able to show that the stars existed way beyond the distance of the moon He was convinced that the planets must orbit the sun, but was unable to develop a satisfying model Accuracy through repetition

27. Johannes Kepler (1571-1630) Worked for Brahe Highly religious Believed in the Heliocentric model Attempted to find a physically realistic model for Mars’ orbit (retrograde motion) This finally lead him to discard the circular orbit

29. Let’s look at what Kepler had for data… Page 573 in your textbook Use the data table and plug these numbers into your graphing calculator Determine if the relationship between Orbital Radius (ie, the distance from the planet to the Sun) and the Orbital Period (how long it takes the planet to orbit the Sun – ie, a year).

30. What type of relationship? Inverse (linear) Logarithmic Exponential

31. Check your “r” values!

32. Kepler’s Laws of Planetary Motion Three Laws that describe the relationships between the motion of the planets

33. Kepler’s Laws of Planetary Motion 1 st Law: The orbits of planets and other celestial bodies around the Sun are ellipses. The Sun is one of the ellipses foci.

35. An ellipse is defined as a figure drawn around 2 points called FOCI, such that the distance from one focus to any point on the figure back to the other focus is a constant

36. Kepler’s Laws of Planetary Motion 2 nd Law: A line from the Planet to the Sun sweeps over equal areas in equal amounts of time http://commons.wikimedia.org/wiki/File:Ellipse_Animation_Small.gif http://www.opencourse.info/astronomy/introduction/05.motion_planets/

37. Why does this happen? Planets move quicker when they are closer to the Sun. This makes it cover more distance.

38. Kepler’s Laws of Planetary Motion 3 rd Law: Deals with the length of time that it takes a planet to orbit the Sun (The Period of Revolution). All planets orbiting the Sun have the same ratio (k). Where r is the planet’s average (mean) distance from the Sun (measured in AU) T is the period of revolution of the planet (measured in years)

39. Kepler’s Laws We now know that k is constant not only for planets but for ALL satellites (even artificial!) orbiting the Earth, the Moon, and the Sun. Note: k is not a true constant. It is only a constant for things orbiting the same celestial body. Example: All planets orbiting the Sun have the same k value. All moons orbiting Jupiter have the same k value. All Kepler’s Laws are true for all satellites.