History of Astronomy

1. History of Astronomy

2. Stonehenge • Dates from Stone Age (2800 B.C.) • Construction spanned 17 centuries

3. Sun Dagger Chaco Canyon, NM • Sliver of light passes through carved stone at noon on the summer solstice

4. Ancient Chinese • Observed the heavens, records of comets • Historical data still used today

5. Ancient Greek Astronomy

6. Ionia – the birthplace of science

7. Greek Models of the Universe • Geocentric (Earth Centered) or Ptolemaic, A.D. 140

8. Ptolemaic model • http://www.csit.fsu.edu/%7Edduke/nmoon6.html

9. Retrograde Motion of Mars

10. Jupiter and Saturn Retrograde motion • http://antwrp.gsfc.nasa.gov/apod/ap011220.html

11. Heliocentric Model (Sun centered) • Aristarchus (290 B. C.), forgotten for 1800 years

12. Great Library of Alexandria

13. Hypatia of Alexandria

14. Astronomy in the Middle Ages

15. Muslim astronomy • Key link from ancient Greeks during Dark Ages • Examples of Muslim terms: Zenith and star names such as Vega, Betelgeuse

16. Nicolaus Copernicus(Mikołaj Kopernik) • Rediscovered Aristarchus’s heliocentric model

17. De revolutionibusorbiumcoelestium(On the Revolutions of the Celestial Spheres) • Published just before his death in 1543 • Starting point of modern astronomy • Placed on the Catholic Church’s Index of Prohibited Books in 1616

18. Galileo Galilei • Built a telescope in 1609 • His work supported Copernicus • Found 4 moons orbiting Jupiter

19. Published SidereusNuncius (The Starry Messenger) in 1610 • Banned in 1616

20. Johannes Kepler • Contemporary of Galileo

21. Kepler’s First Law • The orbital paths of the planets are elliptical, not circular, with the Sun at one focus

22. Kepler’s 1st Law

23. Kepler’s Second Law • An imaginary line connecting the Sun to any planet sweeps out equal areas of the ellipse in equal intervals of time

24. Kepler’s second law • http://www.youtube.com/watch?v=_3OOK8a4l8Y&feature=related • http://www.astro.virginia.edu/class/oconnell/astr121/im/kepler-2ndanim-NS.gif

25. Kepler’s Third Law • The square of a planet’s orbital period is proportional to the cube of its semimajor axis P2 = a3 where P is in Earth years and a is in astronomicalunits • 1 astronomical unit (AU) = avg. distance from the Earth to the Sun

27. Pluto’s semimajor axis (average distance from the Sun) is approximately 40. AU. Calculate the period of Pluto • a = 40. AU And a3 = 64,000 • P2 = a3 • P2 = 64,000 • P = √64,000 • P = 250 years

28. Issac Newton • Published PhilosophiaeNaturalis Principia Mathematica in 1687 • Possibly most influential physics book ever written • Newtonian mechanics  WHY the planets move according to Kepler’s Laws

29. Newton’s inverse square law • The acceleration due to gravity is inversely proportional to the square of the distance

30. 2.8 Newtonian Mechanics Escape speed: the speed necessary for a projectile to completely escape a planet’s gravitational field. With a lesser speed, the projectile either returns to the planet or stays in orbit.

31. Newton’s Cannon • http://galileoandeinstein.physics.virginia.edu/more_stuff/Applets/newt/newtmtn.html

32. 2.7 Newton’s Laws Newton’s first law: An object at rest will remain at rest, and an object moving in a straight line at constant speed will not change its motion, unless an external force acts on it.

33. 2.7 Newton’s Laws Newton’s second law: When a force is exerted on an object, its acceleration is inversely proportional to its mass: a = F/m Newton’s third law: When object A exerts a force on object B, object B exerts an equal and opposite force on object A.

34. 2.7 Newton’s Laws Gravity On the Earth’s surface, acceleration of gravity is approximately constant, and directed toward the center of Earth

35. 2.7 Newton’s Laws Gravity For two massive objects, gravitational force is proportional to the product of their masses divided by the square of the distance between them

36. 2.8 Newtonian Mechanics Kepler’s laws are a consequence of Newton’s laws; first law needs to be modified: The orbit of a planet around the Sun is an ellipse, with the center of mass of the planet–Sun system at one focus.

37. William Hershel • Discovered Uranus (1781), • Key figure of The Age of Enlightenment

38. Caroline Hershel • Discovered several comets

39. Einstein • Annus mirabilis (1905) • Published 4 articles in the AnnalenderPhysik Changed views on space, time, and mattermatter

40. Carl Sagan

41. Steven Hawking • Gravitational singularities • Black holes

42. History of Planetariums • Antikythera mechanism mechanical computer • ~ 100 BC, Greek

43. Jena PlanetariumGermany, 1926

44. Buhl Planetarium

45. Hayden PlanetariumNew York

46. Summary of a few important concepts from chapter 2 • First models of solar system were geocentric but couldn't easily explain retrograde motion • Heliocentric model does; also explains brightness variations • Galileo's observations supported heliocentric model • Kepler found three empirical laws of planetary motion from observations

47. Question 1 a) planets move on epicycles. b) planets orbit the Sun in the same direction. c) Earth moves faster in its orbit. d) they are closer than Uranus. e) they rotate quickly on their axes. Mars, Jupiter, and Saturn show retrograde motion because

48. Question 1 a) planets move on epicycles. b) planets orbit the Sun in the same direction. c) Earth moves faster in its orbit. d) they are closer than Uranus. e) they rotate quickly on their axes. Mars, Jupiter, and Saturn show retrograde motion because As Earth overtakes and “passes” the outer planets, they seem to slow down and reverse direction.

49. Question 2 a) The Earth rotated. b) The Sun rotated. c) The geocentric model couldn’t account for day and night. d) The Earth revolved around the Sun. e) The Sun orbited Earth. How did the geocentric model account for day and night on Earth?

50. Question 2 a) The Earth rotated. b) The Sun rotated. c)The geocentric model couldn’t account for day and night. d) The Earth revolved around the Sun. e)The Sun orbited Earth. How did the geocentric model account for day and night on Earth? The geocentric model held that the Earth was motionless in the center of the universe.