1. For instructors’ eyes only… You may be surprised to learn… …that over 25% of all undergraduate students do not utilize their required course materials. …student retention is dropping nationwide and while the higher education community has done a remarkable job of opening the doors of college to more and more students, we have not seen equal strides in the number of students who actually complete four-year degrees. (Education Trust, 2004) See the next slide on what you can do… Instructor: Course/Section:

2. For instructors’ eyes only… What you can do… The top factors motivating a student to use their adopted books all involve whether the material is immediately used, referred to, or assessed from in the classroom. Please take a few minutes the first day of class to explain and demonstrate why you adopted your book and accompanying technology. The next few slides show the book, technology products, and messaging to students that indicates they will be responsible for the content. Feel free to customize the information or delete from your slide set. Instructor: Course/Section:

3. Michael Seeds – Astronomy: The Solar System and Beyond, 5 th Edition This is your required course material You will need this material for: - tests and quizzes - homework and reading assignments Instructor: Course/Section:

4. Why you need to use the new edition… Astronomy is changing rapidly! The new fifth edition is fully updated to reflect the exciting developments in astronomy, including images from the surface of Titan, gamma ray bursts, volcanism on icy moons, the Kuiper Belt and the status of Pluto, dark energy, the search for water on Mars, supernova explosions, extra solar planets, and much more. Instructor: Course/Section:

5. Instructor: Course/Section: Featuring instant access to online resources selected by your instructor to help you succeed in the course, including: ThomsonNOW…Personalized Study including quizzes and animated versions of key figures from the text! Virtual Astronomy Labs… 20 online, interactive labs focusing on the most important concepts in astronomy. Your ticket to success! REGISTER FOR 1PASS TODAY at www.thomsonedu.com/login !www.thomsonedu.com/login

6. Instructor: Course/Section: ThomsonNOW is a powerful, online learning tool that helps you assess your unique study needs, and is available with each new copy of Seeds - Astronomy, 5 th edition! After taking a diagnostic pretest, you are given a personalized learning plan that links you to the text and the interactive animations! Post-Tests assess student mastery of core chapter concepts; results can be emailed to the instructor! Improve your grade! REGISTER TODAY at www.thomsonedu.com/login !www.thomsonedu.com/login

7. Instructor: Course/Section: Interactive exercises that complement and enhance the topics in the text Students can turn in labs online or print for homework assignments Quizzes at the end of each lab help you test your understanding of key concepts REGISTER TODAY at www.thomsonedu.com/login !www.thomsonedu.com/login

8. The Sky Astronomy: The Solar System and Beyond 5th edition Michael Seeds

9. The Sky “The Southern Cross I saw every night abeam. The sun every morning came up astern; every evening it went down ahead. I wished for no other compass to guide me, for these were true.” - CAPTAIN JOSHUA SLOCUM Sailing Alone around the World Chapter 2

10. The Sky The night sky is the rest of the universe as seen from our planet. –When you look up at the stars, you look out through a layer of air only a few hundred kilometers deep. –Beyond that, space is nearly empty, and the stars are scattered light years apart.

11. The Sky –Here, you will begin your search for the natural laws that govern the universe by trying to understand what the universe looks like.

12. The Sky As you read this chapter, keep in mind that you live on a planet. –Stars are scattered in the void all around you, most very distant and some closer. –Earth rotates on its axis once a day. So, from your viewpoint, the sky appears to rotate once around you each day. –Not only does the sun rise in the East and set in the West, but so do the stars. –This apparent motion is caused by the rotation of our planet.

13. The Sky On a dark night, far from city lights, you can see a few thousand stars in the sky. The Stars

14. The Sky The ancient astronomers organized what they saw by naming stars and groups of stars. –Some of these names survive to this day. You may know a few of these groups of stars as constellations. The Stars

15. The Sky All around the world, ancient cultures celebrated heroes, gods, and mythical beasts by naming groups of stars after them. –You should not be surprised that the constellations do not look like the creatures they represent any more than Columbus, Ohio, looks like Christopher Columbus. –The constellations simply celebrate the most important mythical figures in each culture. Constellations

16. The Sky The constellations named within the Western culture originated in Mesopotamia over 5,000 years ago. –Other constellations were added by Babylonian, Egyptian, and Greek astronomers during the classical age. –Of these ancient constellations, 48 are still in use. Constellations

17. The Sky To the ancients, a constellation was a loose grouping of stars. –Many of the fainter stars were not included in any constellation. Regions of the southern sky, not visible to the ancient astronomers of northern latitudes, were not identified with constellations. Constellations

18. The Sky Constellation boundaries, when they were defined at all, were only approximate. –So, a star like Alpheratz could be thought of as part of Pegasus or part of Andromeda. Constellations

19. The Sky In order to correct these gaps and ambiguities, astronomers in recent centuries have added 40 modern constellations to fill gaps. Constellations

20. The Sky In 1928, the International Astronomical Union established 88 official constellations with clearly defined boundaries. –Thus, a constellation now represents not a group of stars, but an area of the sky. Any star within the region belongs to one, and only one, constellation. Constellations

21. The Sky In addition to the 88 official constellations, the sky contains a number of less formally defined groupings called asterisms. –The Big Dipper, for example, is a well-known asterism that is part of the constellation Ursa Major (Great Bear). –Another asterism is the Great Square of Pegasus, which includes three stars from Pegasus and one (Alpheratz) from Andromeda. Constellations

22. The Sky Although constellations and asterisms are named based on what is visible in the sky, it is important to remember that most of these groups are made up of stars that are not physically associated with one another. Constellations

23. The Sky Some stars may be many times further away than others and moving through space in different directions. –The only thing they have in common is that they lie in approximately the same direction from Earth. Constellations

24. The Sky In addition to naming groups of stars, ancient astronomers named the brighter stars. Modern astronomers still use many of those names. The Names of the Stars

25. The Sky Whereas the names of the constellations are in Latin, the common language of science in Renaissance Europe, most star names derive from ancient Arabic. Although, they have been much altered by the passing of centuries. The Names of the Stars

26. The Sky –The name of Betelgeuse, the bright red star in Orion, for example, comes from the Arabic yad al-jawza, meaning ‘armpit of Jawza (Orion).’ –Aldebaran, the bright red eye of Taurus the bull, comes from the Arabic al-dabar-an, meaning ‘the follower.’ The Names of the Stars

27. The Sky Naming individual stars is not very helpful, because you can see thousands of them and the names do not help you locate stars in the sky. The Names of the Stars

28. The Sky Another way to identify stars is to assign Greek letters to the bright stars in a constellation in the approximate order of brightness. –Thus, the brightest star is usually designated α (alpha), the second brightest β (beta), and so on. The Names of the Stars

29. The Sky In many constellations, the letters follow the order of brightness. –However, in some constellations, by tradition, mistake, or the personal preferences of early chartmakers, there are exceptions. The Names of the Stars

30. The Sky A star’s Greek-letter designation is the Greek letter followed by the genitive (possessive) form of the constellation name. –For example, the brightest star in the constellation Canis Major is α Canis Majoris. This identifies both the star and the constellation and gives a clue to the relative brightness of the star. –Compare this with the ancient name for this star, Sirius, which tells you nothing about location or brightness. The Names of the Stars

31. The Sky This method of identifying a star’s brightness is only approximate. –In order to discuss the sky with precision, you must have an accurate way of referring to the brightness of stars. –For that, you must consult Hipparchus, one of the first great astronomers. The Names of the Stars

32. The Sky Astronomers measure the brightness of stars using the magnitude scale, a system that first appeared in the writings of the ancient astronomer Claudius Ptolemy about 140 AD. –The system may have originated earlier than Ptolemy, and most astronomers attribute it to the Greek astronomer Hipparchus (160-127 BC). The Brightness of Stars

33. The Sky The ancient astronomers divided the stars into six classes. –The brightest were called first-magnitude stars and those that were fainter, second-magnitude. The scale continued downward to sixth-magnitude stars, the faintest visible to the human eye. –Thus, the larger the magnitude number, the fainter the star. This makes sense if you think of the bright stars as first-class stars and the faintest stars visible as sixth-class stars. The Brightness of Stars

34. The Sky –Hipparchus is believed to have compiled the first star catalog, and he may have used the magnitude system in that catalog. –Almost 300 years later, Ptolemy used the magnitude system in his own catalog, and successive generations of astronomers have continued to use the system. The Brightness of Stars

35. The Sky Modern astronomers can measure the brightness of stars to high precision. –So, instead of saying that the star known by the charming name Chort (Theta Leonis) is third magnitude, they can say its magnitude is 3.34. The Brightness of Stars

36. The Sky –If you measure magnitudes, you will discover that some stars are brighter than 1.0. For example, Vega (α Lyrae) is so bright that its magnitude, 0.04, is almost zero. –A few are so bright that the magnitude scale must extend into negative numbers. On this scale Sirius, the brightest star in the sky, has a magnitude of -1.47. The Brightness of Stars

37. The Sky If you use a telescope to search for very faint stars, you can find stars much fainter than the limit for the unaided eye. –Thus, the magnitude system has also been extended to numbers larger than sixth magnitude to include fainter stars. The Brightness of Stars

38. The Sky –These numbers are known as apparent visual magnitudes (m v ), and they describe how the stars look to human eyes observing from Earth. –Although some stars emit large amounts of infrared or ultraviolet light, humans can’t see it. It is not included in the apparent visual magnitude. –The subscript ‘v’ reminds you that you are including only light you can see. The Brightness of Stars

39. The Sky Another problem is distance. –Very distant stars look fainter and nearby stars look brighter. –Apparent visual magnitude ignores the effect of distance and tells only how bright the star looks, as seen from Earth. The Brightness of Stars

40. The Sky Sometimes, it is convenient for astronomers to convert apparent visual magnitude into intensity— a measure of the light energy from a star that hits one square meter in one second. The Brightness of Stars

41. The Sky –A simple relationship connects apparent visual magnitudes and the intensity of starlight. –Thus, modern astronomers can measure the brightness of stars to high precision, while still making comparisons to observations of apparent visual magnitude that go back to the time of Hipparchus. The Brightness of Stars

42. The Sky Nonastronomers sometimes complain that the magnitude scale is awkward. –Why would they think it is awkward, and how did it get that way? Building Scientific Arguments

43. The Sky Two things might make the magnitude scale seem awkward. –First, it seems backward: the bigger the magnitude number, the fainter the star. –Of course, that is because ancient astronomers were not measuring the brightness of stars but rather classifying them, and first-class stars would be brighter than second-class stars. Building Scientific Arguments

44. The Sky –The second awkward feature of the magnitude scale is its mathematical relation to intensity. –If two stars differ by one magnitude, one is about 2.5 times brighter than the other. But, if they differ by two magnitudes, one is 2.5 x 2.5 times brighter. –This mathematical relationship arises because of the way human eyes perceive brightness as ratios of intensity. Building Scientific Arguments

45. The Sky Now, build your own scientific argument to analyze the following question. –If the magnitude scale is so awkward, why do you suppose astronomers have used it for over two millennia? Building Scientific Arguments

46. The Sky Ancient astronomers believed the sky was a great sphere surrounding Earth, with the stars stuck on the inside like thumbtacks in a ceiling. –Modern astronomers know that the stars are scattered through space at different distances, but it is still convenient to think of the sky as a great starry sphere enclosing Earth. The Sky and Its Motion

47. The Sky As you study the sky, you will notice three important points. –One, the sky appears to rotate westward around Earth each day, but that is a consequence of the eastward rotation of Earth. That rotation produces day and night. –Two, astronomers measure distances across the sky as angles and express them as degrees, minutes, and seconds. The Celestial Sphere

48. The Sky –Three, what you can see of the sky depends on where you are on Earth. If you lived in Australia, you would see many constellations and asterisms invisible from North America. –For example, the star Alpha Centauri is in the southern sky and isn’t visible from most of the United States. You could just glimpse it above the southern horizon if you were in Miami, but you could see it easily from Australia. The Celestial Sphere

49. The Sky The celestial sphere is an example of a scientific model, a common feature of scientific thought. –Notice that a scientific model does not have to be true to be useful. The Celestial Sphere

50. The Sky In addition to the daily motion of the sky, Earth’s rotation adds a second motion to the sky that can be detected only over centuries. –Over 2,000 years ago, Hipparchus compared a few of his star positions with those recorded nearly two centuries before and realized that the celestial poles and equator were slowly moving across the sky. –Later astronomers understood that this motion is caused by the top-like motion of Earth. Precession

51. The Sky –If you have ever played with a gyroscope or top, you have seen how the spinning mass resists any change in the direction of its axis of rotation. –The more massive the top and the more rapidly it spins, the more difficult it is to change the direction of its axis of rotation. Precession

52. The Sky –However, you probably recall that the axis of even the most rapidly spinning top moves as it spins, describing the surface of a cone. –The weight of the top tends to make it tip, and this combines with its rapid rotation to make its axis sweep around in a conical motion called precession. Precession

53. The Sky Earth spins like a giant top and is tipped 23.5° from vertical. –Earth’s large mass and rapid rotation keep its axis of rotation pointed toward a spot near the star Polaris, and the axis would not wander if Earth were a perfect sphere. Precession

54. The Sky –However, Earth, because of its rotation, has a slight bulge around its middle, and the gravity of the sun and moon pulls on this bulge. That tends to twist Earth upright in its orbit. –The combination of these forces and Earth’s rotation causes Earth’s axis to precess in a conical motion, taking about 26,000 years for one cycle. Precession

55. The Sky –Because the celestial poles and equator are defined by Earth’s rotational axis, precession moves these reference marks. –We notice no change at all from night to night or year to year, but precise measurements reveal the precessional motion of the celestial poles and equator. Precession

56. The Sky Over centuries, precession has dramatic effects. –Egyptian records show that 4,800 years ago the north celestial pole was near the star Thuban (α Draconis). –The pole is now approaching Polaris and will be closest to it in about 2100. –In around 12,000 years, the pole will have moved to within 5° of Vega (α Lyrae). Precession

57. The Sky –The figure shows the path followed by the north celestial pole. Precession

58. The Sky As you study astronomy, notice the special terms used to describe such things as precession and the celestial sphere. –You need to know those terms, but science is about understanding nature, not about naming its parts. –Keep in mind that science is more than just vocabulary. Precession

59. The Sky Does everyone see the same circumpolar constellations? –Here, you must use your imagination and build your argument with great care. –You can use the celestial sphere as a convenient model of the sky. Building Scientific Arguments

60. The Sky A circumpolar constellation is one that does not set or rise. Building Scientific Arguments

61. The Sky Which constellations are circumpolar depends on your latitude. –If you live on Earth’s equator, you see all the constellations rising and setting, and there are no circumpolar constellations at all. Building Scientific Arguments

62. The Sky –If you live at Earth’s North Pole, all the constellations north of the celestial equator never set, and all the constellations south of the celestial equator never rise. In that case, every constellation is circumpolar. Building Scientific Arguments

63. The Sky –At intermediate latitudes, the circumpolar regions are caps on the sky whose angular radius equals the latitude of the observer. –If you live in Iceland, the caps are very large and, if you live in Egypt, near the equator, the caps are much smaller. Building Scientific Arguments

64. The Sky –For people in Canada, Ursa Major is circumpolar, but people in Mexico see most of this constellation slip below the horizon. From much of the United States, some of the stars of Ursa Major set and some do not. –In contrast, Orion rises and sets as seen from nearly everywhere on Earth. Explorers at Earth’s poles, however, never see Orion rise or set. Building Scientific Arguments

65. The Sky Now, use the argument you have just built. –How would you improve the definition of a circumpolar constellation to clarify the status of Ursa Major? –Would your definition help in the case of Orion? Building Scientific Arguments