The Copernican Revolution

1. The Copernican Revolution Birth of Modern Science Foundations Unit: Part B

2. Introduction • Living in the Space Age • Earth, one planet among many • Orbits the sun, without (serious) question • Vs. the Alternative • Earth was special • the center of all things

3. Introduction • The Radical Transformation of our “View” • Did not happen overnight • Did not happen without controversy and persecution • A humbling process for humankind. • We will look at the historical observations that guided this transformation.

4. The Orbit of the Moon • The Practical Reasons for Early Astronomy • Navigational guide stars (like Polaris) • Planting/Harvesting Seasons • Calendar/Time Keeping • Counting Turns of the Moon

5. The Orbit of the Moon • Understanding Lunar Phases • Brightest Reflector in the sky • Its orbit of the earth causes changes in the amount of sunlight that it reflects in our direction. • It completes a full cycle in roughly 29 days.

6. The Orbit of the Moon • Just like Earth, the moon is normally 50% illuminated, 50% dark. • Depending on orientation we see all, part, or none of the illuminated side. • The phases of the moon are named based on what portion of the illuminated side is visible.

8. The Orbit of the Moon • There are approximately 3-4 days transition between phases of the moon. • New Moon- No illumination visible • Waxing Crescent- Illumination progresses into view each night.

9. The Orbit of the Moon • First Quarter- Half of the illuminated surface (½ of ½ = ¼) • Rises at Noon, Sets at Midnight • Waxing Gibbous- more than half of the Illumination is visible. • Almost Full

10. The Orbit of the Moon • Full Moon- the illuminated surface is fully visible • Moon rises at sunset, sets at sunrise

11. The Orbit of the Moon • Waning Gibbous- The visible illuminated area is receding, but still more than half. • Last (3rd) Quarter- Half of illuminated area • Rises at midnight, sets at noon. • Waning Crescent- less than half visible, approaching new moon.

12. The Orbit of the Moon. • Animation

13. The Orbit of the Moon • Eclipse when some or all of the Sun’s light is blocked by the Earth/Moon. • Lunar Eclipse • Earth casts a shadow that blocks sunlight to the moon. • Two Regions of Shadow • Umbra- Darkest Shadow • Penumbra- Lighter Shadow

14. The Orbit of the Moon

15. The Orbit of the Moon • Total Lunar Eclipse- Entirely in the Umbra • Partial Lunar Eclipse- Only part of the moon is in the umbra. • Some light still reaches the moon, but must pass through the earth’s atmosphere. Copperish Color.

16. The Orbit of the Moon • Solar Eclipse- The moon passes between Earth and Sun, casting a shadow. • Two Regions of shadow • Umbra • Penumbra

17. The Orbit of the Moon • Total Eclipse- seen within the Umbra • Corona is visible

18. The Orbit of the Moon • Partial Eclipse- seen within the Penumbra

19. The Orbit of the Moon • Annular Eclipse- Moon is too far for the Umbra to cast on the surface of Earth (½ of all Solar Eclipses) • Not all of the sun’s disk is blocked by the moon.

20. The Orbit of the Moon • If the moon and earth continually pass in front of the sun, why don’t we have more eclipses? • The Moon’s Orbit plane is tilted 5.2o from the ecliptic plane. • Eclipse occurs only during alignment as the moon is crossing the ecliptic plane. • New Moon  Solar Eclipse • Full Moon  Lunar Eclipse

21. The Orbit of the Moon • Animation

22. The Orbit of the Moon • Visible Eclipses through 2020

23. The Motions of the Planets • Ancient Astronomers recognized the steady pattern of movement of the Sun, Moon, and Stars. • There were five other bodies in the sky, whose motion was not so easily understood. • The planets • Mercury, Venus, Mars, Jupiter, and Saturn

25. The Motions of the Planets • The Planets • These 5, visible to the naked eye. • Usually shift eastward from night to night • Speed up and slow down • Occasionally appear to loop back westward. • Retrograde Motion • Planetes- Greek word meaning “Wanderer”

26. The Motions of the Planets

27. The Motions of the Planets • Ancient Astronomers (Astrologers)- • Wanted detailed knowledge of the Solar system • Correctly reasoned planet brightness related to distance. • System needed to account for variable brightness and wandering motion of the planets.

28. The Motions of the Planets • Geocentric View (earth center) • Follows teachings of Aristotle (300’s BC) • Works great for Sun, Moon, Stars, but not planets • Needs improvements

29. The Motions of the Planets • Epicyclic Model- • Each planet orbits an imaginary point, that in turn orbits the earth. • Begins to explain retrograde and variable brightness • Doesn’t hold up to new observations.

30. The Motions of the Planets • Ptolemaic Model- (Ptolemy 100’s CE) • Develops small adjustments to Epicycles • Shifts focus from Earth’s center • Requires 80 circular paths to fully explain Sun, Moon, and 5 planets.

31. The Motions of the Planets • Two Main Flaws- • Geocentric Assumption • Insistence on uniform circles

32. The Motions of the Planets • The Heliocentric View- • Aristarchus (300’s BC), not widely accepted • Geocentric Model • Ptolemaic accepted for 13 Centuries • Good Reasoning, Bad Conclusions due to inadequate data • Nicholas Copernicus (1473-1543) • Rediscovers Aristarchus’ heliocentric model.

33. The Motions of the Planets • Copernican View • Earth rotates on its axis and orbits the sun. • Accounts for Variable brightness, retrograde motion. • Motivation: Simplicity

34. The Motions of the Planets • Retrograde occurs when we pass a planet orbiting the same side of the sun.

35. The Motions of the Planets • Reality: Still too complex, retains Greek Epicycles • Gains little acceptance in his lifetime. • Book On the Revolution of the Celestial Spheres, published in 1543.

36. The Birth of Modern Astronomy • Copernicus ideas are advanced by two well known scientists. • Galileo Galilei • Johannes Kepler

37. The Birth of Modern Astronomy • Telescope invented in Holland, early 1600’s • Galileo builds his own by 1609, makes several discoveries. • The Moon has terrain similar to earth. • The sun has imperfections, and rotates • Jupiter has at least 4 moons orbiting it. • Venus has a complete cycle of phases (like Moon)

38. The Birth of Modern Astronomy • Every discovery seems to add to the Copernican Model.

39. The Birth of Modern Astronomy

40. The Birth of Modern Astronomy

41. The Birth of Modern Astronomy • Galileo, publishes his findings supporting the Heliocentric view. • 1616- Named a heretic, work banned. • Continues to publish • Inquisition- House arrest in 1633 til death in 1642 • 1992 The Church forgives his “Crimes”

42. The Laws of Planetary Motion • Johannes Kepler • Laws for Planetary Motion (theoretical) • Based on Data taken by Tycho Brahe. • Kepler became Brahe’s assistant in Prague in 1600 • Brahe dies in 1601 • Kepler inherits Data taken decades Prior, spends the next 29 years analyzing it.

43. The Laws of Planetary Motion • Looking for a simple explanation for planetary motion within Copernican model. • Three Laws 1. A planet’s orbital path is elliptical, with the sun at One Focus. Semi-Major Axis- Half of the Long side Eccentricity- distance between foci/major axis

44. The Laws of Planetary Motion

45. The Laws of Planetary Motion 2. A planet sweeps out equal area in equal time. Moves fastest at the closest point (Perihelion) Moves slowest at the furthest point (Aphelion) Animation

46. The Laws of Planetary Motion 3. The square of the orbital period proportional the cube of the semi-major axis. P- Period in Earth years a- Semi-Major Axis in “astronomical units” 1 A.U. = Earth’s SMA, average Earth-Sun distance

47. The Laws of Planetary Motion • The Power of Kepler’s Laws • Gives us an accurate scale for the solar system. • RADAR puts that scale into concrete measurements • 1 A.U. = 149, 597,870 km (92,975,680 miles)

48. The Laws of Planetary Motion

49. Newton’s Laws • Kepler’s Laws- • Determined Emperically (observation) • What makes the planets follow these Laws? • Best Theoretical Explanation • Isaac Newton (1642-1727) • Laws of Motion • Universal Gravitation • Calculus

50. Newton’s Laws • Three Laws of Motion • An object at rest, remains at rest; An object in motion maintains its motion, unless acted on by a Net External Force. • An object’s acceleration is proportional to the Net force acting on it, and inversely proportional to mass. • For every Force, there is an equal and opposite reaction Force.