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© 2010 Pearson Education, Inc. Chapter 3 The Science of Astronomy.

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1 © 2010 Pearson Education, Inc. Chapter 3 The Science of Astronomy

2 © 2010 Pearson Education, Inc. How did astronomical observations benefit ancient societies? Keeping track of time and seasons – for practical purposes, including agriculture – for religious and ceremonial purposes Aid to navigation Astrology (at least into the 1980s)

3 © 2010 Pearson Education, Inc. Ancient people of central Africa (6500 BC) could predict seasons from the orientation of the crescent moon

4 © 2010 Pearson Education, Inc. Days of week were named for Sun, Moon, and visible planets

5 © 2010 Pearson Education, Inc. What did ancient civilizations achieve in astronomy? Daily timekeeping Tracking the seasons and calendar Monitoring lunar cycles Monitoring planets and stars Predicting eclipses And more …

6 © 2010 Pearson Education, Inc. Egyptian obelisk: Shadows tell time of day.

7 © 2010 Pearson Education, Inc. England: Stonehenge (completed around 1550 B.C.)Archaeoastronomy

8 © 2010 Pearson Education, Inc. England: Stonehenge (1550 B.C.)

9 © 2010 Pearson Education, Inc. New Mexico: Anasazi kiva aligned north-south

10 © 2010 Pearson Education, Inc. SW United States: “Sun Dagger” marks summer solstice

11 © 2010 Pearson Education, Inc. Peru: Lines and patterns, some aligned with stars.

12 © 2010 Pearson Education, Inc. Macchu Pichu, Peru: Structures aligned with solstices.

13 © 2010 Pearson Education, Inc. South Pacific: Polynesians were very skilled in art of celestial navigation

14 © 2010 Pearson Education, Inc. France: Cave paintings from 18,000 B.C. may suggest knowledge of lunar phases (29 dots)

15 © 2010 Pearson Education, Inc. China: Earliest known records of supernova explosions (1400 B.C.) Bone or tortoise shell inscription from the 14th century BC. "On the Xinwei day the new star dwindled." "On the Jisi day, the 7th day of the month, a big new star appeared in the company of the Ho star."

16 © 2010 Pearson Education, Inc. 3.2 Ancient Greek Science Why does modern science trace its roots to the Greeks? How did the Greeks explain planetary motion? How was Greek knowledge preserved through history? Our goals for learning:

17 © 2010 Pearson Education, Inc. Greeks were the first people known to make models of nature. They tried to explain patterns in nature without resorting to myth or the supernatural. Greek geocentric model (c. 400 B.C.) Why does modern science trace its roots to the Greeks?

18 © 2010 Pearson Education, Inc. Special Topic: Eratosthenes Measures Earth (c. 240 B.C.) Calculate circumference of Earth: 7/360  (circum. Earth) = 5000 stadia  circum. Earth = 5000  360/7 stadia ≈ 250,000 stadia Measurements: Syene to Alexandria distance ≈ 5000 stadia angle = 7° Compare to modern value (≈ 40,100 km): Greek stadium ≈ 1/6 km  250,000 stadia ≈ 42,000 km

19 © 2010 Pearson Education, Inc. Underpinnings of the Greek geocentric model: How did the Greeks explain planetary motion? Earth at the center of the universe Heavens must be “perfect”: Objects moving on perfect spheres or in perfect circles. Aristotle Plato

20 © 2010 Pearson Education, Inc. But this made it difficult to explain apparent retrograde motion of planets… Review: Over a period of 10 weeks, Mars appears to stop, back up, then go forward again.

21 © 2010 Pearson Education, Inc. The most sophisticated geocentric model was that of Ptolemy (A.D ) — the Ptolemaic model: Sufficiently accurate to remain in use for 1,500 years. Arabic translation of Ptolemy’s work named Almagest (“the greatest compilation”) Ptolemy

22 © 2010 Pearson Education, Inc. So how does the Ptolemaic model explain retrograde motion? Planets really do go backward in this model..

23 © 2010 Pearson Education, Inc. 3.3 The Copernican Revolution How did Copernicus, Tycho, and Kepler challenge the Earth-centered model? What are Kepler’s three laws of planetary motion? How did Galileo solidify the Copernican revolution? Our goals for learning:

24 © 2010 Pearson Education, Inc. How did Copernicus, Tycho, and Kepler challenge the Earth-centered model? Copernicus ( ) Proposed a Sun-centered model (published 1543) Used model to determine layout of solar system (planetary distances in AU) But... The model was no more accurate than the Ptolemaic model in predicting planetary positions, because it still used perfect circles.

25 © 2010 Pearson Education, Inc. Tycho Brahe ( ) Compiled the most accurate (one arcminute) naked eye measurements ever made of planetary positions. Still could not detect stellar parallax, and thus still thought Earth must be at center of solar system (but recognized that other planets go around Sun). Hired Kepler, who used Tycho’s observations to discover the truth about planetary motion.

26 © 2010 Pearson Education, Inc. Kepler first tried to match Tycho’s observations with circular orbits But an 8-arcminute discrepancy led him eventually to ellipses. “If I had believed that we could ignore these eight minutes [of arc], I would have patched up my hypothesis accordingly. But, since it was not permissible to ignore, those eight minutes pointed the road to a complete reformation in astronomy.” Johannes Kepler ( )

27 © 2010 Pearson Education, Inc. An ellipse looks like an elongated circle. What is an ellipse?

28 © 2010 Pearson Education, Inc. Kepler’s First Law: The orbit of each planet around the Sun is an ellipse with the Sun at one focus. What are Kepler’s three laws of planetary motion?

29 © 2010 Pearson Education, Inc. Kepler’s Second Law: As a planet moves around its orbit, it sweeps out equal areas in equal times. This means that a planet travels faster when it is nearer to the Sun and slower when it is farther from the Sun.

30 © 2010 Pearson Education, Inc. More distant planets orbit the Sun at slower average speeds, obeying the relationship p 2 = a 3 p = orbital period in years a = avg. distance from Sun in AU Kepler’s Third Law

31 © 2010 Pearson Education, Inc. Thought Question An asteroid orbits the Sun at an average distance a = 4 AU. How long does it take to orbit the Sun? A.4 years B.8 years C.16 years D.64 years Hint: Remember that p 2 = a 3

32 © 2010 Pearson Education, Inc. A.4 years B.8 years C.16 years D.64 years We need to find p so that p 2 = a 3. Since a = 4, a 3 = 4 3 = 64. Therefore, p = 8, p 2 = 8 2 = 64. Thought Question An asteroid orbits the Sun at an average distance a = 4 AU. How long does it take to orbit the Sun?

33 © 2010 Pearson Education, Inc. How did Galileo solidify the Copernican revolution? Galileo overcame major objections to the Copernican view. Three key objections rooted in Aristotelian view were: 1.Earth could not be moving because objects in air would be left behind. 2.Non-circular orbits are not “perfect” as heavens should be. 3.If Earth were really orbiting Sun, we’d detect stellar parallax.

34 © 2010 Pearson Education, Inc. Galileo’s experiments showed that objects in air would stay with Earth as it moves. Overcoming the first objection (nature of motion): Aristotle thought that all objects naturally come to rest. Galileo showed that objects will stay in motion unless a force acts to slow them down (Newton’s first law of motion).

35 © 2010 Pearson Education, Inc. Overcoming the second objection (heavenly perfection): Tycho’s observations of comet and supernova already challenged this idea. Using his telescope, Galileo saw: Sunspots on Sun (“imperfections”) Mountains and valleys on the Moon (proving it is not a perfect sphere)

36 © 2010 Pearson Education, Inc. Tycho thought he had measured stellar distances, so lack of parallax seemed to rule out an orbiting Earth. Galileo showed stars must be much farther than Tycho thought — in part by using his telescope to see the Milky Way is countless individual stars. If stars were much farther away, then lack of detectable parallax was no longer so troubling. Overcoming the third objection (parallax):

37 © 2010 Pearson Education, Inc. Galileo also saw four moons orbiting Jupiter, proving that not all objects orbit Earth.

38 © 2010 Pearson Education, Inc. Galileo’s observations of phases of Venus proved that it orbits the Sun and not Earth.

39 © 2010 Pearson Education, Inc. Galileo’s trial

40 © 2010 Pearson Education, Inc. Galileo’s trial Galileo Pope Urban VIII

41 © 2010 Pearson Education, Inc. Papal Infallibility “His definitions, of themselves, and not from the consent of the Church, are justly held irreformable, for they are pronounced with the assistance of the Holy Spirit, an assistance promised to him in blessed Peter." And if you did not agree with the Church sanctioned doctrines And if you did not agree with the Church sanctioned doctrines:

42 © 2010 Pearson Education, Inc.

43 "The Bible was written to show us how to go to heaven, not how the heavens go." - Cardinal Baronius (1598), a quote cited by Galileo 43

44 © 2010 Pearson Education, Inc. Galileo Galilei The Catholic Church ordered Galileo to recant his claim that Earth orbits the Sun in 1633 and banned his book. The trial was soon viewed as a clash between dogma and free thinking and helped reducing the political power of the church. His book on the subject was removed from the Church’s index of banned books in 1824.

45 © 2010 Pearson Education, Inc. exoneration In 1992, 359 years after the Galileo trial and 350 years after his death, Pope John Paul II established a commission that ultimately issued an apology, lifting the edict of Inquisition against Galileo.

46 © 2010 Pearson Education, Inc. How can we distinguish science from non-science? Defining science can be surprisingly difficult. Science from the Latin scientia, meaning “knowledge.” 3.4 The Nature of Science

47 © 2010 Pearson Education, Inc. The idealized scientific method Based on proposing and testing hypotheses Based on proposing and testing hypotheses hypothesis = educated guess hypothesis = educated guess Observations and experiments are key Observations and experiments are key More accurate observations distinguish between different hypotheses More accurate observations distinguish between different hypotheses

48 © 2010 Pearson Education, Inc. But science rarely proceeds in this idealized way… For example: Sometimes we start by “just looking” then coming up with possible explanations. Sometimes we follow our intuition rather than a particular line of evidence.

49 © 2010 Pearson Education, Inc. Hallmarks of Science: #1 Modern science seeks explanations for observed phenomena that rely solely on natural causes. (A scientific model cannot include divine intervention)

50 © 2010 Pearson Education, Inc. Hallmarks of Science: #2 Science progresses through the creation and testing of models of nature that explain the observations as simply as possible. (Simplicity = “Occam’s razor”)

51 © 2010 Pearson Education, Inc. Hallmarks of Science: #3 A scientific model must make testable predictions about natural phenomena that would force us to revise or abandon the model if the predictions do not agree with observations. In other words a scientific model must be falsifiable. (Karl Popper)

52 © 2010 Pearson Education, Inc.

53 Not all knowledge comes from science Suppose you are shopping for a car: You might make observations, exercise logic, test hypotheses, but this pursuit is clearly not science, because it is not directed at developing a testable explanation for observed natural phenomenon. There is nothing wrong with this knowledge!

54 © 2010 Pearson Education, Inc. What about our apprehensions and fear of science?

55 © 2010 Pearson Education, Inc. Spiritual value of science 1.The universe is not capricious and vengeful. 2.There is beauty and order beyond our wildest ancient dreams. 3.Unity and symmetry: The entire universe is made of the same elements and obey the same physical laws

56 © 2010 Pearson Education, Inc.

57 Our Precious Birthright Scientific progress: The cumulative growth of a system of knowledge over time in which useful features are retained and based on non useful features are abandoned, based on the rejection or confirmation of testable knowledge the rejection or confirmation of testable knowledge.

58 © 2010 Pearson Education, Inc. What is a scientific theory? The word theory has a different meaning in science than in everyday life. In science, a theory is NOT the same as a hypothesis, rather: A scientific theory must: —Explain a wide variety of observations with a few simple principles, AND —Must be supported by a large, compelling body of evidence. —Must NOT have failed any crucial test of its validity.

59 © 2010 Pearson Education, Inc. Thought Question Darwin’s theory of evolution meets all the criteria of a scientific theory. This means: A.Scientific opinion is about evenly split as to whether evolution really happened. B.Scientific opinion runs about 90% in favor of the theory of evolution and about 10% opposed. C.After more than 100 years of testing, Darwin’s theory stands stronger than ever, having successfully met every scientific challenge to its validity. D.There is no longer any doubt that the theory of evolution is absolutely true.

60 © 2010 Pearson Education, Inc. Thought Question Darwin’s theory of evolution meets all the criteria of a scientific theory. This means: A.Scientific opinion is about evenly split as to whether evolution really happened. B.Scientific opinion runs about 90% in favor of the theory of evolution and about 10% opposed. C.After more than 100 years of testing, Darwin’s theory stands stronger than ever, having successfully met every scientific challenge to its validity. D.There is no longer any doubt that the theory of evolution is absolutely true.

61 © 2010 Pearson Education, Inc. 3.5 Astrology How is astrology different from astronomy? Does astrology have any scientific validity? Other paranormal claims Our goals for learning:

62 © 2010 Pearson Education, Inc. How is astrology different from astronomy? Astronomy is a science focused on learning about how stars, planets, and other celestial objects work. Astrology is a search for hidden influences on human lives based on the positions of planets and stars in the sky.

63 © 2010 Pearson Education, Inc. Does astrology have any scientific validity? Scientific tests have shown that astrological predictions are no more accurate than we should expect from pure chance.

64 © 2010 Pearson Education, Inc. Astrological Time Twins A study involving 2,101 persons born in London during 3–9 March They were born on average 4.8 minutes astrologers apart, so they were precisely those for which astrologers had predicted ‘really exceptional similarities of life and temperament’. Measurements at ages 11, 16 and 23 had provided test scores for IQ, reading and arithmetic; teacher and parent ratings of behavior such as anxiety, aggressiveness and sociability self-ratings of ability such as art, music and sports; and various others such as occupation, accident proneness and marital status;

65 © 2010 Pearson Education, Inc. No correlation was found! The effect size due to astrology was 0.00 ± It disconfirms the idea of sun signs (2,101 Pisceans evidently had few similarities!)It disconfirms the idea of sun signs (2,101 Pisceans evidently had few similarities!)

66 © 2010 Pearson Education, Inc. What is the credible evidence for fringe phenomena? Astrology Psychokinesis ESP Clairvoyance Crystals Numerology ET visits Channeling Crop circles Tarot reading Pyramidology Palmistry J.J. Abrams Alien abductions Divination Bible code

67 © 2010 Pearson Education, Inc. Why is it important? If any of these phenomena has factual validity it will have a profound impact on the way we understand the world around us. For this reason: Extraordinary claims demand Extraordinary proof.

68 © 2010 Pearson Education, Inc. James Randi has become a foremost spokesperson on behalf of critical thinking, reason and a willingness to ask questions -- especially when claims are made concerning the paranormal or spiritual.

69 © 2010 Pearson Education, Inc. JREF million-dollar paranormal challenge The James Randi Educational Foundation offer a one-million-dollar prize to anyone who can show, under proper observing conditions, evidence of any paranormal, supernatural, or occult power or event.

70 © 2010 Pearson Education, Inc. Reading Time to move on to Chapter 4!


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