Hewitt/Lyons/Suchocki/Yeh Conceptual Integrated Science

1. Hewitt/Lyons/Suchocki/YehConceptual Integrated Science Chapter 28 THE UNIVERSE

2. This lecture will help you understand: • Observing the Night Sky • The Brightness and Colors of Stars • The Hertzsprung-Russell Diagram • The Life Cycles of Stars • Black Holes • Galaxies • The Big Bang • Quasars

3. Observing the Night Sky Observing the Night Sky Constellations are groups of stars named over antiquity. A familiar constellation is Ursa Major, the Great Bear.

4. Observing the Night Sky The monthly constellations seen in the night sky change as Earth’s path around the Sun progresses.

5. Observing the Night Sky Can you see that during a solar eclipse, the darkened daytime sky would show constellation positions as normally seen six months earlier or later?

6. Observing the Night Sky The Big Dipper is a well-known constellation. The pairs of stars at the end of its bowl point to Polaris, the North Star.

7. Observing the Night Sky The seven stars of the Big Dipper are at very different distances from Earth.

8. Observing the Night Sky A time-exposure of the night sky shows streaks of stars from our “carousel Earth.”

9. Observing the Night Sky CHECK YOUR NEIGHBOR Knowing the names of the constellations tells us much about the A. stars that comprise them. • people in the cultures that named them. • difference between stars and planets. • all of the above.

10. Observing the Night Sky CHECK YOUR ANSWER Knowing the names of the constellations tells us much about the A. stars that comprise them. • people in the cultures that named them. • difference between stars and planets. • all of the above. Explanation: The names of constellations tell us nothing about the makeup of the stars that compose them. They are more interesting historically.

11. The Brightness and Colorsof Stars A star’s color indicates its temperature: • A red star is cooler than a blue star • A blue star is almost twice as hot as a red star (blue light has almost twice the frequency of red light in accord with   T)

12. The Brightness and Colors of Stars CHECK YOUR NEIGHBOR Which of these stars radiates light of the longest wavelength? A. Red star. • Yellow star. • Blue star. • Violet star.

13. The Brightness and Colors of Stars CHECK YOUR ANSWER Which of these stars radiates light of the longest wavelength? A. Red star. • Yellow star. • Blue star. • Violet star. Explanation: The longest wavelength is emitted by the star with the lowest frequency, the red-hot star. (If the question had asked for the highest frequency, that would be emitted by the violet star.)

14. The Brightness and Colors of Stars Brightness of a star is of two kinds: • Apparent brightness—the brightness as it appears to us • Luminosity—the intrinsic brightness, independent of how bright it appears The luminosity of stars is compared to that of the Sun, which is noted LSun.

15. The Brightness and Colors of Stars CHECK YOUR NEIGHBOR We see the Sun’s luminosity as LSun. If we were on a spaceship twice as far away from the Sun, its apparent brightness would appear A. the same. • half as much. • one quarter as much. • four times as much.

16. The Brightness and Colors of Stars CHECK YOUR ANSWER We see the Sun’s luminosity as LSun. If we were on a spaceship twice as far away from the Sun, its apparent brightness would appear A. the same. • half as much. • one quarter as much. • four times as much. Explanation: In accordance with the inverse-square law, twice as far away means one quarter the brightness.

17. The Hertzsprung-Russell Diagram Graph of intrinsic brightness versus surface temperature for stars Note: positions that form a main sequence for average stars, and exotic stars above or below the main sequence The H-R diagram is to an astronomer what the Periodic Table is to a chemist.

18. The Hertzsprung-Russell Diagram CHECK YOUR NEIGHBOR On the H-R diagram, the Sun is A. an average star. • seen to be special. • a low-temperature star. • especially bright.

19. The Hertzsprung-Russell Diagram CHECK YOUR ANSWER On the H-R diagram, the Sun is A. an average star. • seen to be special. • a low-temperature star. • especially bright.

20. The Hertzsprung-Russell Diagram CHECK YOUR NEIGHBOR A dying star that has collapsed to a small size and is cooling off would appear in which part of the H-R diagram? A. Lower left. • Upper left. • Lower right. • Upper right.

21. The Hertzsprung-Russell Diagram CHECK YOUR ANSWER A dying star that has collapsed to a small size and is cooling off would appear in which part of the H-R diagram? A. Lower left. • Upper left. • Lower right. • Upper right. Explanation: Such a star would be a white dwarf.

22. The Life Cycles of Stars Life cycle of stars: • Begins as a nebula • Advances to a protostar • Becomes a star when fusion in its core occurs Depending on its mass, the star may become a red giant and then burn out to become a white dwarf.

23. The Life Cycles of Stars White dwarf: • Cools for eons until it is too cold to emit light • If part of a binary, pulls matter from its partner, which can lead to a nuclear blast (nova)

24. The Life Cycles of Stars Final stage of more massive stars is collapse, then an explosion called a supernova. Remnant of a supernova is the Crab Nebula

25. The Life Cycles of Stars CHECK YOUR NEIGHBOR The source of energy in the Sun and stars is A. chemical reactions. • thermonuclear reactions. • both of the above. • none of the above.

26. The Life Cycles of Stars CHECK YOUR ANSWER The source of energy in the Sun and stars is A. chemical reactions. • thermonuclear reactions. • both of the above. • none of the above. Explanation: The Sun and other stars are balls of plasma, much too hot for chemical reactions to occur.

27. Black Holes Black hole: • What remains when a supergiant star collapses into itself • Named because gravitation at its surface is so intense that even light cannot escape

28. Black Holes Black hole Why gravitation at the surface of a star increases when it collapses star shrinks to half its radius  gravitation at its surface increases by 4 (inverse-square law)

29. Black Holes CHECK YOUR NEIGHBOR When a star collapses to one-tenth size, gravitation at its surface becomes A. one tenth as much. • the same. • 10 times as much. • 100 times as much.

30. Black Holes CHECK YOUR ANSWER When a star collapses to one-tenth size, gravitation at its surface becomes A. one tenth as much. • the same. • 10 times as much. • 100 times as much. Explanation: This follows from the inverse-square law introduced in Chapter 5.

31. Black Holes CHECK YOUR NEIGHBOR When a giant star collapses to become a black hole, gravity is greatly increased A. at it surface. • at its center. • in all surrounding space. • all of the above.

32. Black Holes CHECK YOUR ANSWER When a giant star collapses to become a black hole, gravity is greatly increased A. at its surface. • at its center. • in all surrounding space. • all of the above. Explanation: It is important to know that gravitation increases mainly at the surface of the collapsed star. Gravity at the surface before collapse is the same at that same distance from the center of the black hole after collapse.

33. Black Holes CHECK YOUR NEIGHBOR If the Sun collapsed to become a black hole, the orbit of Earth would A. remain unchanged. • be pulled inward toward the black hole. • spiral outward away from the black hole. • be a straight-line path.

34. Black Holes CHECK YOUR ANSWER If the Sun collapsed to become a black hole, the orbit of Earth would A. remain unchanged. • be pulled inward toward the black hole. • spiral outward away from the black hole. • be a straight-line path. Explanation: F = G(m1  m2)/d2. Letting this equation guide our thinking, we see that none of its terms differ. Although the density of the black hole has greatly increased, its mass is the same before and after collapse. Because the mass of Earth and the solar black hole are the same, and distance between centers is the same, the force holding Earth in orbit wouldn’t change. Equations nicely guide thinking!

35. Galaxies Galaxy: • A huge assemblage of stars, interstellar gas, and dust • Most familiar—Milky Way

36. Galaxies Three types of galaxies: • Elliptical • Irregular • Spiral This is a giant elliptical galaxy M87.

37. Galaxies A pair of irregular galaxies— the Large Magellanic Cloud and neighboring Small Magellanic Cloud.

38. Galaxies This is Spiral Galaxy M83, thought to be much like our Milky Way. Galaxies are not the largest things in the universe. There are clusters of galaxies, and then galaxy superclusters—larger than can be imagined!

39. Galaxies CHECK YOUR NEIGHBOR The most common galaxies are A. elliptical galaxies. • irregular galaxies. • spiral galaxies. • clusters of galaxies.

40. Galaxies CHECK YOUR ANSWER The most common galaxies are A. elliptical galaxies. • irregular galaxies. • spiral galaxies. • clusters of galaxies.

41. The Big Bang Big Bang: • Theory—our universe began with a primordial explosion some 13.7 billion years ago • Marks the beginning of space and time

42. The Big Bang Evidence for the Big Bang: • Continuing expansion of the universe • Measured cosmic background radiation, predicted before it was discovered and measured • Measurements of element abundances, predicted before measured • Findings—early universe was much hotter than now

43. The Big Bang CHECK YOUR NEIGHBOR Scientific evidence supports the date of the Big Bang event at A. 7000 years ago. • 100,000 years ago. • 5 billion years ago. • 13.7 billion years ago.

44. The Big Bang CHECK YOUR ANSWER Scientific evidence supports the date of the Big Bang event at A. 7000 years ago. • 100,000 years ago. • 5 billion years ago. • 13.7 billion years ago.

45. Quasars Quasars are: • The brightest objects in the universe • The oldest known objects in the universe • May be the brilliant cores of very distant galaxies as seen when young • Are the most puzzling objects known to astronomers

46. Quasars CHECK YOUR NEIGHBOR When we speak of a quasar, we are talking about A. the Big Bang. • a black hole. • a neutron star. • none of the above.

47. Quasars CHECK YOUR ANSWER When we speak of a quasar, we are talking about A. the Big Bang. • a black hole. • a neutron star. • none of the above. Explanation: Quasars are currently the most puzzling objects known to astronomers. Exactly what they are is currently being researched.