How to Use This Presentation

1. How to Use This Presentation • To View the presentation as a slideshow with effects select “View” on the menu bar and click on “Slide Show.” • To advance through the presentation, click the right-arrow key or the space bar. • From the resources slide, click on any resource to see a presentation for that resource. • From the Chapter menu screen click on any lesson to go directly to that lesson’s presentation. • You may exit the slide show at any time by pressing the Esc key.

2. Resources Bellringers Chapter Presentation Transparencies Standardized Test Prep Visual Concepts

3. The Universe Chapter 20 Table of Contents Section 1 The Life and Death of Stars Section 2 The Milky Way and Other Galaxies Section 3 Origin of the Universe

4. Section 1 The Life and Death of Stars Chapter 20 Objectives • Describethe basic structure and properties of stars. • Explain how the surface temperature of a star is measured. • Recognizethat all normal stars are powered by fusion reactions that form elements. • Identifythe stages in the evolution of stars.

5. Section 1 The Life and Death of Stars Chapter 20 Bellringer Based on what you have learned, as well as previous knowledge, write answers for the following items: 1. People have studied the stars for centuries. The ancient Greeks gave names to groups of stars called constellations. Make a list of at least five constellations. 2. Explain why scientists collect information from electromagnetic waves, such as visible light, microwaves, and X rays, to study stars. 3. Stars do not all look the same. Some are brighter than others, and many have different colors. Write a paragraph suggesting the causes of these differences.

6. Section 1 The Life and Death of Stars Chapter 20 What Are Stars? • Star a large celestial body that is composed of gas and that emits light; the sun is a typical star • Light-year the distance that light travels in one year; about 9.5 trillion kilometers • Stars are huge spheres of hot gas. • The nearest star to the Earth is the sun. • We use the unit light-year to describe a star’s distance from Earth.

7. Section 1 The Life and Death of Stars Chapter 20 What Are Stars? continued • Stars are driven by nuclear fusion reactions. • The core of a star is extremely hot, extremely dense, and under extreme pressure. • Nuclear fusion takes place in the core of a star. • Fusion combines the nuclei of hydrogen atoms into helium. • When two particles fuse, energy is released.

8. Section 1 The Life and Death of Stars Chapter 20 Constellation

9. Section 1 The Life and Death of Stars Chapter 20 Nuclear Fusion

10. Section 1 The Life and Death of Stars Chapter 20 What Are Stars? continued • Energy moves slowly through the layers of a star. • Energy moves through the layers of a star by convection and radiation. • Convection rising hot gas moves upward, away from the star’s center, and cooler gas sinks toward the center • Radiation atoms absorb energy and transfer it to other atoms in random directions; atoms near the star’s surface radiate energy into space.

11. Section 1 The Life and Death of Stars Chapter 20 Structure of the Sun

12. Section 1 The Life and Death of Stars Chapter 20 Structure of the Sun

13. Section 1 The Life and Death of Stars Chapter 20 The Sun’s Atmosphere

14. Section 1 The Life and Death of Stars Chapter 20 Studying Stars • Why do some stars appear brighter than others? • The brightness of a star depends on the star’s temperature, size, and distance from Earth. • The brightest star in the night sky, Sirius, appears so bright because it is relatively close to Earth.

15. Section 1 The Life and Death of Stars Chapter 20 Studying Stars, continued • We learn about stars by studying light. • Stars produce a full range of electromagnetic radiation, from high-energy X-rays to low-energy radio waves. • Scientists use optical telescopes to study visible light and radio telescopes to study radio waves emitted from astronomical objects. • Earth’s atmosphere blocks some wavelengths, so telescopes in space can study a wider range of the spectrum.

16. Section 1 The Life and Death of Stars Chapter 20 Studying Stars, continued • A star’s color is related to its temperature. • Hotter objects glow with light that has shorter wavelengths (closer to the blue end of the spectrum). • Cooler objects glow with light that has longer wavelengths (closer to the red end of the spectrum.)

17. Section 1 The Life and Death of Stars Chapter 20 Starlight Intensity Graph

18. Section 1 The Life and Death of Stars Chapter 20 Studying Stars, continued • Spectral lines reveal the composition of stars. • The spectra of most stars have dark lines caused by gases in the outer layers that absorb light at that wavelength. • Each element produces a unique pattern of spectral lines. • Astronomers can match the dark lines in starlight to the known lines of elements found on Earth.

19. Section 1 The Life and Death of Stars Chapter 20 The Fate of Stars • The sun formed from a cloud of gas and dust. • Stars are born, go through different stages of development, and eventually die. • The sun formed about 5 billion years ago. • Stars appear different from one another in part because they are at different stages in their life cycles.

20. Section 1 The Life and Death of Stars Chapter 20 The Fate of Stars, continued • The sun now has a balance of inward and outward forces • The fusion reactions in the core of the sun produce an outward force that balances the inward force due to gravity. • Over time, the percentage of the sun’s core that is helium becomes larger. • Eventually the core will run out of hydrogen and the sun will begin to die. • Scientists estimate that the sun can continue nuclear fusion for another 5 billion years.

21. Section 1 The Life and Death of Stars Chapter 20 The Fate of Stars, continued • The sun will become a red giant before it dies. • As fusion slows, the outer layers of the sun will expand. • The sun will become a red giant. • Red giant a large, reddish star late in its life cycle • When the sun runs out of helium, the outer layers will expand and eventually leave the sun’s orbit. • The sun will become a white dwarf. • White dwarf a small, hot dim star that is the leftover center of an old star.

22. Section 1 The Life and Death of Stars Chapter 20 The Fate of Stars, continued • Supergiant stars explode in supernovas. • Massive stars evolve faster, develop hotter cores, and create heavier elements through fusion. • A supergiant forms iron at it’s core. • Eventually the core collapses and then explodes in a Type II supernova. • Supernova a gigantic explosion in which a miassive star collapses and throws its outer layers into space, plural supernovae

23. Section 1 The Life and Death of Stars Chapter 20 The Fate of Stars, continued • A Type I supernova occurs when a white dwarf in a binary system (a system composed of two stars) collects enough mass from its companion to exceed 1.4 solar masses.

24. Section 1 The Life and Death of Stars Chapter 20 The Fate of Stars, continued • After a Type II supernova, either a neutron star or a black hole forms. • If the core that remains after a supernova has a mass of 1.4 to 3 solar masses, the remnant can become a neutron star. • If the leftover core has a mass that is greater than three solar masses, it will collapse to form a black hole. • Black hole an object so massive and dense that not even light can escape its gravity

25. Section 1 The Life and Death of Stars Chapter 20 The Fate of Stars, continued • The H-R diagram shows how stars evolve. • The vertical line on an H-R diagram indicates brightness in absolute magnitude. • The horizontal line on the H-R diagram indicates temperature. • Most stars appear in a diagonal line called the main sequence. • As stars age and pass through different stages, their positions on the H-R diagram change.

26. Section 1 The Life and Death of Stars Chapter 20 H-R Diagram

27. Section 1 The Life and Death of Stars Chapter 20 Types of Stars

28. Section 2 The Milky Way and Other Galaxies Chapter 20 Objectives • Definegalaxy, and identify Earth’s home galaxy. • Describetwo characteristics of a spiral galaxy. • Distinguishbetween the three types of galaxies. • Describetwo aspects of a quasar, and identify the tools scientists use to study quasars.

29. Section 2 The Milky Way and Other Galaxies Chapter 20 Bellringer Based on what you have learned, as well as previous knowledge, answer the following questions: 1. What types of objects would you expect to find within a galaxy? 2. Do you think that the same force that keeps our solar system together keeps galaxies together?

30. Section 2 The Milky Way and Other Galaxies Chapter 20 Bellringer, continued 3. Do you think that the components of galaxies move in a random and unpredictable motion, or do they move in an ordered and predictable one? 4. The word galaxy comes from the Greek word for “milk,” and the star-rich region of our own galaxy has long been called the Milky Way. Other galaxies, before they were recognized as containing stars, were called nebulas, from the Latin for “clouds.” What do you think was the reason these starry regions were described in these terms?

31. Section 2 The Milky Way and Other Galaxies Chapter 20 Galaxies • Galaxies contain millions or billions of stars. • Galaxy a collection of stars, dust, and gas bound together by gravity • Because stars age at different rates, a galaxy may contain many types of stars.

32. Section 2 The Milky Way and Other Galaxies Chapter 20 Galaxies, continued • Gravity holds galaxies together in clusters. • Galaxies are not spread evenly throughout space. • Cluster a group of stars or galaxies bound by gravity • The Milky Way galaxy and the Andromeda galaxy are two of the largest members of the Local Group, a cluster of more than 30 galaxies. • Clusters of galaxies can form even larger groups, called superclusters.

33. Section 2 The Milky Way and Other Galaxies Chapter 20 Types of Galaxies • We live in the Milky Way galaxy. • Edwin Hubble divided all galaxies into three major types: spiral, elliptical, and irregular. • Most of the objects visible in the night sky are part of the Milky Way galaxy. • Scientists use astronomical data to piece together a picture of the Milky Way galaxy.

34. Section 2 The Milky Way and Other Galaxies Chapter 20 Types of Galaxies, continued • The Milky Way is a spiral galaxy. • Our galaxy is a huge spiraling disk of stars, gas, and dust. • Our solar system is located within a spiral arm. • The nucleus of the galaxy is dense and has many old stars. • The gas and dust is called interstallar matter. • Interstellar matter the gas and dust located between the stars in a galaxy.

35. Section 2 The Milky Way and Other Galaxies Chapter 20 Types of Galaxies, continued • Eliptical galaxies have no spiral arms. • Elliptical galaxies are spherical or egg shaped. • They contain mostly older stars and have little interstellar matter. • Because older stars are red, elliptical galaxies often have a reddish color.

36. Section 2 The Milky Way and Other Galaxies Chapter 20 Types of Galaxies, continued • All other galaxies are irregular galaxies. • Irregular galaxies lack regular shapes and do not have a well-defined structure. • Some irregular galaxies may be oddly shaped because the gravitational influence of nearby galaxies distorts their spiral arms.

37. Section 2 The Milky Way and Other Galaxies Chapter 20 Investigating Different Types of Galaxies

38. Section 2 The Milky Way and Other Galaxies Chapter 20 How Galaxies Evolve • Quasars may be infant galaxies. • In 1960, a faint object was matched with a strong radio signal. This object was called a quasar. • quasar quasi-stellar radio sources; very luminous objects that produce energy at a high rate and that are thought to be the most distant objects in the universe • Each quasar has a huge central black hole and a large disk of gas and dust around it.

39. Section 2 The Milky Way and Other Galaxies Chapter 20 How Galaxies Evolve, continued • Galaxies change over time. • Galaxies change as they use up their stores of gas and dust • Galaxies also change as a result of collisions. • As galaxies approach each other, mutual gravitational attraction changes their shape. • Collisions of gas and dust may cause new stars to begin forming.

40. Section 2 The Milky Way and Other Galaxies Chapter 20 Formation of the Solar System

41. Section 2 The Milky Way and Other Galaxies Chapter 20 Lunar Phases

42. Section 2 The Milky Way and Other Galaxies Chapter 20 Solar and Lunar Eclipses

43. Chapter 20 Section 3 Origin of the Universe Objectives • Describethe basic structure of the universe. • Describered shift, and explain what it tells scientists about our universe. • Statethe main features of the big bang theory, and explain the evidence supporting the expansion of the universe. • Explainhow scientists are using tools and models to hypothesize what may happen to the universe in the future.

44. Chapter 20 Section 3 Origin of the Universe Bellringer Based on what you have learned, as well as previous knowledge, answer the following questions: 1. What types of objects would you expect to find within a galaxy? 2. Do you think that the same force that keeps our solar system together keeps galaxies together?

45. Chapter 20 Section 3 Origin of the Universe Bellringer 3. Do you think that the components of galaxies move in a random and unpredictable motion, or do they move in an ordered and predictable one? 4. The word galaxy comes from the Greek word for “milk,” and the star-rich region of our own galaxy has long been called the Milky Way. Other galaxies, before they were recognized as containing stars, were called nebulas, from the Latin for “clouds.” What do you think was the reason these starry regions were described in these terms?

46. Chapter 20 Section 3 Origin of the Universe What Is the Universe? • Universe the sum of all space, matter, and energy that exist, that have existed in the past, and that will exist in the future. • You are part of the universe, as is Earth and everything on it.

47. Chapter 20 Section 3 Origin of the Universe Cosmology

48. Chapter 20 Section 3 Origin of the Universe What is the Universe? continued • We see the universe now as it was in the past. • It takes time for light to travel in space. • The farther away an object is, the older the light that we receive from that object. • Most of the universe is empty space • Space is a vacuum with no air and no air pressure.

49. Chapter 20 Section 3 Origin of the Universe What Happened at the Beginning? • The universe is expanding. • Observations of spectral lines from other galaxies indicated that they were moving away from us • Red shift an apparent shift toward longer wavelengths of light caused when a luminous object moves away from the observer • Blue shift an apparent shift toward shorter wavelengths of light caused when a luminous object moves toward the observer

50. Chapter 20 Section 3 Origin of the Universe Red Shift