Of men and Models

1. Of men and Models History of Astronomy

2. models • Good scientific model of the universe • 2 Characteristics • Explains observations • Good universe model must explain movements of sun, moon, stars, and planets • Makes predictions of future positions of sun, moon, etc…

3. archaeostronomy • Stonehenge • Started in 3000BC finished 1800BC • Fist a circular ditch with a pathway • Stone outside facing the path • Found astronomical alignments at Stonehenge and could be possible eclipse predictor • Never will know

4. The Greeks Aristotle 384-322 bc • First principle- something that is obviously true • Used logic and reasoning of first principle perfection of heavens • First principle is true so anything based on that is true • 2 parts of universe- Earth and Heavens • Earth is imperfect and changeable • Heavens re perfect and unchanging • Earth is a sphere • Traveler saw new constellations and the bow of a ship • Shadow of earth during eclipse is round

5. The Greeks Aristotle • Geocentric model • Earth centered system • 55 crystalline spheres that carried the planets moon and Sun across the sky

6. Greeks Aristarchus • First to say that the Earth was not the center of the universe, but this was unknown until it was read in the writings of Archimedes • None of the works by Aristarchus survived • Estimated the relatives distances of the Sun and the Moon from Earth by using angular observations

7. Aristarchus • Looked at half moon and was at a 90 degree angle between Sun and Earth • Found angle between Moon Earth and Sun to be 87 degrees • Wrong numbers but correct method

8. Aristarchus • Said Sun is 7 times bigger but is actually closer to 100 times • Said moon’s diameter is .32 times and is .27 times

9. Greeks Ptolemy 140AD Geocentric model Made it possible to predict the positions of planets This was the first good model could close to accurately predict the locations of the planets would be for a given time

10. Greeks Ptolemy • Planets sometimes look as though they are moving backwards • Retrograde motion • http://www.scienceu.com/observatory/articles/retro/retro.html • In order to explain the observation, he assumed that each planet revolved in a small orbit called an epicycle • The center of the epicycle then revolved about the Earth on a much larger circle

12. Copernicus • 16th century • “On the Revolution of Heavenly Bodies” 1545 • Heliocentric-sun centered • Showed that the planetary motions can be explained much more simply by assuming that all the planets, including Earth, orbit the Sun • explained the apparent “retrograde” motion of Mars, Jupiter, and Saturn and the fact that Mercury and Venus never move more than a certain distance from the sun • His ideas were not widely accepted until more than 100 years later

13. Copernicus • A very important aspect of Copernicus’ model was the concept of a universe in which the distances of the planets from the sun bore a direct relationship to the size of their orbits • Meaning a greater the radius of the orbit, the greater the distance from the Sun • This lead to a new ordering of the planets • He also coined the term astronomical unit AU- the distance from the Earth to the sun

14. Tycho Brahe • Eccentric • Kidnapped • Rich • Lost his nose in a duel over a mathematical equation • Pet Elk • Jepp • Horrible way to die

15. Tychobrahe • Did not follow the heliocentric model • Discovered a new star (now known as a supernova or an exploding star) • Found that it was not moving in relation to the other stars using parallax • Changes in the perfect heavens • Observed a comet in 1577 and determined it was farther away than the moon by using parallax

16. paralax Try it out! p simulation

17. Tycho Brahe • Made extraordinary observations • Built a special building specifically for his observation of the night sky • Uraniborg • Recorded the location of stars and planets onto a perfect brass globe

18. Tycho Brahe • His model • Did not agree with the Ptolemy model because he saw the superova • Did not agree with Copernicus because he could not see movement of star • Happy Medium

19. Tycho • Geocentric • The Sun and Moon revolve around the Earth, and the other five planets revolve around the Sun.

20. Johannes Kepler1571-1630 • Accepted the Copernican model • Worked on him own but needed the observations of Brahe to back up his theories • Became a math teacher • During a lesson found what he thought might be the key to the structure of the universe

21. Kepler • Thought that the obits of the heavenly bodies would be arranged in different polygons • Didn’t work • BUT WAIT! ITS 3D! • Moved to spheres

22. Kepler • Tycho Brahewas interested in his publication of MysteriumCosmographicum • Lost his job and Tycho invited him to work with him. • Keppler needed Tycho’s information • Tycho kept stringing him along • When Tycho died he finally passed along his information and his tools • Keppler found that Mars had an eliptical path

23. Kepler • 3 laws of planetary motion • Law of ellipses • Law of equal Areas • Harmonic Law

24. Law of ellipses • The orbit of the planet is an ellipse with the sun at one focus • The planet has a place in their orbit when they are closest to the sun (perihelion -147 mil km earth - sun), and when they are farthest away (aphelion 152-mil km earth - sun) • Rp = radius of orbit at perhelion • Ra = radius of orbit at aphelion

25. What is an ellipse? • Not a circle • How close is it from being a circle? • Eccentricity Increasing eccentricity

26. eccentricity • Ranges from 0-1 • A circle has an e of • 0 • A parabola has an e of 1 • So… and ellipse has an e of • 0<e<1

28. eccentricity • Figure out Earths е • Ra = 1.52 x1010 and Rp = 1.47 x1010 • е = 0.0167

29. Planets sweep out equal areas of space in equal time. Therefore, the planets velocities are not uniform Planet speeds up at perihelion Slows down at aphelion Perihelion and Aphelion Law of equal areas

30. Equal Areas • A = ½ bh A’ = ½ b’h’ • A = A’ • equal areas

31. There is a direct relationship between the distance from the sun and the planet’s angular velocity When Kepler first published his third law in 1619, the mathematical statement of it looked like this: p2 x a3 = k P period of orbit, a is semi major axis (1/2 major axis), k is a constant which is unique for every body under consideration Newton later changed it Harmonic Law

32. p2α a3 The square of the orbital period of a planet is directly proportional to the cube of the semi-major axis of its orbit. What this implies is that in bigger orbits it takes longer to go around, for TWO reasons:      (1) you have further to go in bigger orbits      (2) you move slower in bigger orbits Harmonic Law

33. Harmonic • What this implies is that in bigger orbits it takes longer to go around, for TWO reasons:      (1) you have further to go in bigger orbits      (2) you move slower in bigger orbits • We use T2/R3

34. Pluto’s orbit is 100 times bigger than Mercury’s So, you have 100 times further to go (approx) In addition, Pluto goes 10 times (sqrt of 100) slower than Mercury Pluto takes 1000 times as long to go around i.e. ¼ of a millennium rather than ¼ of a year Examples of Kepler’s law at work

35. Saturn’s orbit is a little over 9 times bigger than ours Moves little more than 3 times slower than we do (sqrt of 9), It takes a little more than 9 times 3 (=27) times as long, to go around Examples of Kepler’s law at work

36. Galileo Galilee 1564-1642 • Known as the father of the scientific method • First to use the telescope to disprove Ptolemy’s model

37. Galileo • His greatest fame is for discoveries in astronomy • moons of Jupiter • phases of Venus • He also changed the views on motion and falling bodies • Same acceleration rate • Newton named it 9.8 m/s2

38. Galileo • Downward motion required a force and sideways motion required no force • http://videos.howstuffworks.com/discovery/29420-assignment-discovery-aristotle-galileo-and-gravity-video.htm • He determined the natural horizontal motion was due to a property of matter he called “inertia.” • Inertial movement will continue if not acted upon by an outside force • He determined the natural horizontal motion was due to a property of matter he called “inertia.” • Inertial movement will continue if not acted upon by an outside force.