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2. Resources Chapter Presentation Visual Concepts Transparencies Standardized Test Prep Brain Food Video Quiz

3. Chapter 30 Stars, Galaxies, and the Universe Table of Contents Section 1 Characterstics of Stars Section 2 Stellar Evolution Section 3 Star Groups Section 4 The Big Bang Theory

4. Section 1 Characteristics of Stars Chapter 30 Objectives • Describehow astronomers determine the compositions and temperature of stars. • Explainwhy stars appear to move in the sky. • Describeone way astronomers measure the distances to stars. • Explainthe difference between absolute magnitude and apparent magnitude.

5. Section 1 Characteristics of Stars Chapter 30 Analyzing Starlight star a large celestial body that is composed of gas and that emits light. • Nuclear fusion is the combination of light atomic nuclei to form heavier atomic nuclei • Astronomers learn about stars by analyzing the light that the stars emit. • Starlight passing through a spectrograph produces a display of colors and lines called a spectrum.

6. Section 1 Characteristics of Stars Chapter 30 Analyzing Starlight, continued • All stars have dark-line spectra, which are bands of color crossed by dark lines where the color is diminished. • A star’s dark-line spectrum reveals the star’s composition and temperature. • Stars are made up of different elements in the form of gases. • Because different elements absorb different wavelengths of light, scientists can determine the elements that make up a star by studying its spectrum.

7. Section 1 Characteristics of Stars Chapter 30 The Compositions of Stars • Scientists have learned that stars are made up of the same elements that compose Earth. • The most common element in stars is hydrogen. • Helium is the second most common element in star. • Small quantities of carbon, oxygen, and nitrogen are also found in stars.

8. Section 1 Characteristics of Stars Chapter 30 The Temperatures of Stars • The temperature of most stars ranges from 2,800˚C to 24,000˚C. • Blue stars have average surface temperatures of 35,000˚C. • Yellow stars, such as the sun, have surface temperatures of about 5,500˚C. • Red stars have average surface temperatures of 3,000˚C.

9. Section 1 Characteristics of Stars Chapter 30 The Sizes and Masses of Stars • Stars vary in size and mass. • Stars such as the sun are considered medium-sized stars. The sun has a diameter of 1,390,000 km. • Most stars visible from Earth are medium-sized stars. • Many stars also have about the same mass as the sun, however some stars may be more or less massive.

10. Section 1 Characteristics of Stars Chapter 30 Stellar Motion Apparent Motion • The apparent motion of stars is the motion visible to the unaided eye. Apparent motion is caused by the movement of Earth. • The rotation of Earth causes the apparent motion of stars sees as though the stars are moving counter-clockwise around the North Star. • Earth’s revolution around the sun causes the stars to appear to shift slightly to the west every night.

11. Section 1 Characteristics of Stars Chapter 30 Stellar Motion, continued Reading Check Why does Polaris appear to remain stationary in the night sky?

12. Section 1 Characteristics of Stars Chapter 30 Stellar Motion, continued Reading Check Why does Polaris appear to remain stationary in the night sky? Polaris is almost exactly above the pole of Earth’s rotational axis, so Polaris moves only slightly around the pole during one rotation of Earth.

13. Section 1 Characteristics of Stars Chapter 30 Stellar Motion, continued Circumpolar Stars • Some stars are always visible in the night sky. These stars never pass below the horizon. • In the Northern Hemisphere, the movement of these stars makes them appear to circle the North Star. • These circling stars are called circumpolar stars.

14. Section 1 Characteristics of Stars Chapter 30 Stellar Motion, continued Actual Motion of Stars • Most stars have several types of actual motion. • Stars rotate on an axis. • Some stars may revolve around another star. • Stars either move away from or toward our solar system.

15. Section 1 Characteristics of Stars Chapter 30 Stellar Motion, continued Actual Motion of Stars • Doppler effect an observed change in the frequency of a wave when the source or observer is moving • The spectrum of a star that is moving toward or away from Earth appears to shift, due to the Doppler effect. • Stars moving toward Earth are shifted slightly toward blue, which is called blue shift. • Stars moving away from Earth are shifted slightly toward red, which is called red shift.

16. Section 1 Characteristics of Stars Chapter 30 Stellar Motion, continued The spectrum of a star that is moving toward or away from Earth appears to shift, as shown in the diagram below.

17. Section 1 Characteristics of Stars Chapter 30 Distances to Stars • light-year the distance that light travels in one year. • Distances between the stars and Earth are measured in light-years. • parallax an apparent shift in the position of an object when viewed from different locations. • For relatively close stars, scientists determine a star’s distance by measuring parallax.

18. Section 1 Characteristics of Stars Chapter 30 Light-Year

19. Section 1 Characteristics of Stars Chapter 30 Stellar Brightness • Apparent magnitude the brightness of a star as seen from the Earth. • The apparent magnitude of a star depends on both how much light the star emits and how far the star is from Earth. • Absolute magnitude the brightness that a star would have at a distance of 32.6 light-years from Earth • The brighter a star is, the lower the number of its absolute magnitude.

20. Section 1 Characteristics of Stars Chapter 30 Stellar Brightness The lower the number of the star on the scale shown on the diagram below, the brighter the star appears to observers.

21. Section 1 Characteristics of Stars Chapter 30 Absolute and Apparent Motion

22. Chapter 30 Section 2 Stellar Evolution Objectives • Describehow a protostar becomes a star. • Explainhow a main-sequence star generates energy. • Describethe evolution of a star after its main-sequence stage.

23. Chapter 30 Section 2 Stellar Evolution Classifying Stars • Main sequence the location on the H-R diagram where most stars lie; it has a diagonal pattern from the lower right to the upper left. • One way scientists classify stars is by plotting the surface temperatures of stars against their luminosity. The H-R diagram is the graph that illustrates the resulting pattern. • Astronomers use the H-R diagram to describe the life cycles of stars. Most stars fall within a band that runs diagonally through the middle of the H-R diagram. These stars are main sequence stars.

24. Chapter 30 Section 2 Stellar Evolution Classifying Stars, continued • Main sequence the location on the H-R diagram where most stars lie; it has a diagonal pattern from the lower right to the upper left. • One way scientists classify stars is by plotting the surface temperatures of stars against their luminosity. The H-R diagram is the graph that illustrates the resulting pattern. • Astronomers use the H-R diagram to describe the life cycles of stars. Most stars fall within a band that runs diagonally through the middle of the H-R diagram. These stars are main sequence stars.

25. Chapter 30 Section 2 Stellar Evolution Classifying Stars, continued

26. Chapter 30 Section 2 Stellar Evolution Star Formation • nebula a large cloud of gas and dust in interstellar space; a region in space where stars are born. • A star beings in a nebula. When the nebula is compressed, some of the particles move close to eaother and are pulled together by gravity. • As described in Newton’s law of universal gravitation, as gravity pulls particles of the nebula closer together, the gravitational pull of the particles on each other increases. • As more particles come together, regions of dense matter begin to build up within the cloud.

27. Chapter 30 Section 2 Stellar Evolution Star Formation, continued Protostars • As gravity makes dense regions within a nebula more compact, these regions spin and shrink and begin to form a flattened disk.The disk has a central concentration of matter called a protostar. • The protostar continues to contract and increase in temperature for several million years. Eventually the gas in the region becomes so hot that its electrons are stripped from their parent atoms. • The nuclei and free electrons move independently, and the gas is then considered a separate state of matter called plasma.

28. Chapter 30 Section 2 Stellar Evolution Star Formation, continued The Birth of a Star • A protostar’s temperature continually increases until it reaches about 10,000,000°C. • At this temperature, nuclear fusion begins. Nuclear fusion is a process in which less-massive atomic nuclei combine to form more-massive nuclei. The process releases enormous amounts of energy. • The onset of nuclear fusion marks the birth of a star. Once this process begins, it can continue for billions of years.

29. Chapter 30 Section 2 Stellar Evolution Star Formation,continued A Delicate Balancing Act • As gravity increases the pressure on the matter within the star, the rate of fusion increase. • In turn, the energy radiated from fusion reactions heats the gas inside the star. • The outward pressures of the radiation and the hot gas resist the inward pull of gravity. • This equilibrium makes the star stable in size.

30. Chapter 30 Section 2 Stellar Evolution Star Formation, continued Reading Check How does the pressure from fusion and hot gas interact with the force of gravity to maintain a star’s stability?

31. Chapter 30 Section 2 Stellar Evolution Star Formation, continued Reading Check How does the pressure from fusion and hot gas interact with the force of gravity to maintain a star’s stability? The forces balance each other and keep the star in equilibrium. As gravity increases the pressure on the matter within a star, the rate of fusion increases. This increase in fusion causes a rise in gas pressure. As a result, the energy from the increased fusion and gas pressure generates outward pressure that balances the force of gravity.

32. Chapter 30 Section 2 Stellar Evolution The Main-Sequence Stage • The second and longest stage in the life of a star is the main-sequence stage. During this stage, energy continues to be generated in the core of the star as hydrogen fuses into helium. • A star that has a mass about the same as the sun’s mass stays on the main sequence for about 10 billion years. • Scientists estimate that over a period of almost 5 billion years, the sun has converted only 5% of its original hydrogen nuclei into helium nuclei.

33. Chapter 30 Section 2 Stellar Evolution Leaving the Main Sequence Giant Stars giant a very large and bright star whose hot core has used most of its hydrogen. • A star enters its third stage when almost all of the hydrogen atoms within its core have fused into helium atoms. billion years. • A star’s shell of gases grows cooler as it expands. As the gases in the outer shell become cooler, they begin to glow with a reddish color. These stars are known as giants.

34. Chapter 30 Section 2 Stellar Evolution Leaving the Main Sequence, continued Supergiants • Main-sequence stars that are more massive than the sun will become larger than giants in their third stage. • These highly luminous stars are called supergiants. These stars appear along the top of the H-R diagram.

35. Chapter 30 Section 2 Stellar Evolution Leaving the Main Sequence, continued Reading Check Where are giants and supergiants found on the H-R diagram?

36. Chapter 30 Section 2 Stellar Evolution Leaving the Main Sequence, continued Reading Check Where are giants and supergiants found on the H-R diagram? Giants and supergiants appear in the upper right part of the H-R diagram.

37. Chapter 30 Section 2 Stellar Evolution The Final Stages of a Sunlike Star Planetary Nebulas • As the star’s outer gases drift away, the remaining core heats these expanding gases. • The gases appear as a planetary nebula, a cloud of gas that forms around a sunlike star that is dying.

38. Chapter 30 Section 2 Stellar Evolution The Final Stages of a Sunlike Star, continued White Dwarfs • As a planetary nebula disperses, gravity causes the remaining matter in the star to collapse inward. • The matter collapses until it cannot be pressed further together. • A hot, extremely dense core of matter - a white dwarf - is left. White dwarfs shine for billions of years before they cool completely. • The gases appear as a planetary nebula, a cloud of gas that forms around a sunlike star that is dying.

39. Chapter 30 Section 2 Stellar Evolution The Final Stages of a Sunlike Star, continued Novas and Supernovas nova a star that suddenly becomes brighter • Some white dwarfs revolve around red giants. When this happeneds, the gravity of the whit dwarf may capture gases from the red giant. • As these gases accumulate on the surface of the white dwarf, pressure begins to build up. • This pressure may cause large explosions. These explosions are called novas.

40. Chapter 30 Section 2 Stellar Evolution The Final Stages of a Sunlike Star, continued Novas and Supernovas • A white dwarf may also become a supernova, which is a star that has such a tremedous explosion that it blows itself apart. • The explosions of supernovas completely destroy the white dwarf star and may destroy much of the red giant.

41. Chapter 30 Section 2 Stellar Evolution The Final Stages of Massive Stars Supernovas in Massive Stars • Massive stars become supernovas as part of their life cycle. • After the supergiant stage, the star collapses, producing such high temperatures that nuclear fusion begins again. • When nuclear fusion stops, the star’s core begins to collapse under its own gravity. This causes the outer layers to explode outward with tremendous force.

42. Chapter 30 Section 2 Stellar Evolution The Final Stages of Massive Stars, continued Reading Check What causes a supergiant star to explode as a supernova?

43. Chapter 30 Section 2 Stellar Evolution The Final Stages of Massive Stars, continued Reading Check What causes a supergiant star to explode as a supernova? Giants and supergiants appear in the upper right part of the H-R diagram.

44. Chapter 30 Section 2 Stellar Evolution The Final Stages of Massive Stars, continued Neutron Stars neutron star a star that has collapsed under gravity to the point that the electrons and protons have smashed together to form neutrons • Stars more massive than the sun do not become white dwarfs. • After a star explodes as a supernova, the core may contract into a neutron star.

45. Chapter 30 Section 2 Stellar Evolution The Final Stages of Massive Stars, continued

46. Chapter 30 Section 2 Stellar Evolution Types of Stars

47. Chapter 30 Section 2 Stellar Evolution The Final Stages of Massive Stars, continued Pulsars pulsar a rapidly spinning neutron star that emits pulses of radio and optical energy • Some neutron stars emit a beam of radio waves that sweeps across space and are detectable here on Earth. • These stars are called pulsars. For each pulse detected on Earth, we know that the star has rotated within that period.

48. Chapter 30 Section 2 Stellar Evolution The Final Stages of Massive Stars, continued Black Holes black hole an object so massive and dense that even light cannot escape its gravity • Some massive stars produce leftovers too massive to become a stable neutron star. • These stars contract, and the force of the contratction leaves a black hole.

49. Chapter 30 Section 3 Star Groups Objectives • Describethe characteristics that identify a constellation. • Describethe three main types of galaxies. • Explainhow a quasar differs from a typical galaxy.

50. Chapter 30 Section 3 Star Groups Constellations Dividing Up the Sky constellation one of 88 regions into which the skay has been divided in order to describe the locations of celestial objects; a group of stars organized in a recognizable pattern • In 1930, astronomers around the world agreed upon a standard set of 88 constellations. • You can use a map of the constellations to locate a particular star.