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Chapter Twenty-Seven: Stars

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Title: PowerPoint Presentation Author: kat Last modified by: Valarie Gray Created Date: 3/8/2000 5:59:36 PM Document presentation format: On-screen Show (4:3) – PowerPoint PPT presentation

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Title: Chapter Twenty-Seven: Stars


1
Chapter Twenty-Seven Stars
  • 27.1 The Sun
  • 27.2 Stars
  • 27.3 The Life Cycle of Stars

2
NGC 3532 in the constellation Carina
ESO/G.Beccari
3
27.2 How are stars classified?
  • Astronomers classify stars according to

4
27.2 How are stars classified?
  • Astronomers classify stars according to
  • size/mass,

5
27.2 How are stars classified?
  • Astronomers classify stars according to
  • size/mass,
  • temperature,

6
27.2 How are stars classified?
  • Astronomers classify stars according to
  • size/mass,
  • temperature,
  • color, and

7
27.2 How are stars classified?
  • Astronomers classify stars according to
  • size/mass,
  • temperature,
  • color, and
  • brightness.

8
27.2 What is the size of stars?
  • Stars come in a range of sizes and masses.

9
27.2 What is the size of stars?
  • Stars come in a range of sizes and masses.
  • Our Sun is a medium-sized star.

10
27.2 What is the size of stars?
  • Stars come in a range of sizes and masses.
  • Our Sun is a medium-sized star.
  • The largest stars, giant stars have a mass of
    about 60 times the mass of the Sun.

11
  • The sun is considered a __________ star.
  • Giant
  • Medium-sized
  • Dwarf

12
27.2 The size of stars
  • There are two types of giant stars.

13
27.2 The size of stars
  • What are two types of giant stars?
  • Red giants are cooler than white stars.

14
27.2 The size of stars
  • What are two types of giant stars?
  • Red giants are cooler than white stars.
  • Blue giant stars are hot and much more massive
    than our sun.

15
  • Which star is cooler, a blue giant or a red
    giant?

16
27.2 The size of stars
  • Stars that are smaller than the sun come in two
    main categories, dwarfs and neutron stars.

17
27.2 The size of stars
  • Stars that are smaller than the sun come in two
    main categories, dwarfs and neutron stars.
  • Sirius, the Dog Star, is the largest known white
    dwarf.

18
27.2 How is temperature and color related with
stars?
  • If you look closely at the stars on a clear
    night, you might see a slight reddish or bluish
    tint to some stars.

19
27.2 How is temperature and color related with
stars?
  • If you look closely at the stars on a clear
    night, you might see a slight reddish or bluish
    tint to some stars.
  • This is because their surface temperatures are
    different.

20
27.2 Temperature and color
  • The color of light is related to its energy.

21
27.2 Temperature and color
  • The color of light is related to its energy.
  • White light is a mixture of all colors at equal
    brightness.

22
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23
27.2 Brightness and luminosity
  • Brightness, also called intensity, describes the
    amount of light energy per second falling on a
    surface.

24
27.2 Brightness and luminosity
  • For a distant source of light like a star, the
    brightness decreases as the inverse square of the
    distance.

25
What does the inverse square law mean?

26
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27
27.2 Brightness and luminosity
  • Luminosity is the total amount of light given off
    by a star in all directions.
  • .

28
27.2 Brightness and luminosity
  • Luminosity is the total amount of light given off
    by a star in all directions.
  • Luminosity is a fundamental property of a star
    whereas brightness depends on both luminosity and
    distance.

29
27.2 Temperature and luminosity
  • In the early 1900s, Danish astronomer Ejnar
    Hertzsprung and American astronomer Henry Russell
    developed an important tool for studying stars.

30
27.2 Temperature and luminosity
  • In the early 1900s, Danish astronomer Ejnar
    Hertzsprung and American astronomer Henry Russell
    developed an important tool for studying stars.
  • Their graph showed luminosity on the y axis

31
27.2 Temperature and luminosity
  • In the early 1900s, Danish astronomer Ejnar
    Hertzsprung and American astronomer Henry Russell
    developed an important tool for studying stars.
  • Their graph showed luminosity on the y axis
  • and surface temperature on the x axis

32
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33
27.2 Temperature and luminosity
  • H-R diagrams are useful because they help
    astronomers categorize stars into groups

?
34
27.2 Temperature and luminosity
  • H-R diagrams are useful because they help
    astronomers categorize stars into groups
  • Main sequence stars, like the Sun, are in a very
    stable part of their life cycle.

35
27.2 Temperature and luminosity
  • H-R diagrams are useful because they help
    astronomers categorize stars into groups
  • Main sequence stars, like the Sun, are in a very
    stable part of their life cycle.
  • White dwarfs are hot and dim and cannot be seen
    without a telescope.

36
27.2 Temperature and luminosity
  • H-R diagrams are useful because they help
    astronomers categorize stars into groups
  • Main sequence stars, like the Sun, are in a very
    stable part of their life cycle.
  • White dwarfs are hot and dim and cannot be seen
    without a telescope.
  • Red giants are cool and bright and some can be
    seen without a telescope.

37
27.2 Temperature and luminosity
  • H-R diagrams are useful because they help
    astronomers categorize stars into groups
  • Main sequence stars, like the Sun, are in a very
    stable part of their life cycle.
  • White dwarfs are hot and dim and cannot be seen
    without a telescope.
  • Red giants are cool and bright and some can be
    seen without a telescope.

Can you locate blue giants on the H-R diagram?
38
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39
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40
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41
Chapter Twenty-Seven Stars
  • 27.1 The Sun
  • 27.2 Stars
  • 27.3 The Life Cycle of Stars

42
27.3 The life cycle of stars
  • A star, regardless of its size, begins its life
    inside a huge cloud of gas (mostly hydrogen) and
    dust called a nebula.

43
27.3 The life cycle of stars
  • A star, regardless of its size, begins its life
    inside a huge cloud of gas (mostly hydrogen) and
    dust called a nebula.
  • The Eagle Nebula is the birthplace of many stars.

44
27.3 The life cycle of stars
  • A protostar is the earliest stage in the life
    cycle of a star.

45
27.3 The life cycle of stars
  • A protostar is the earliest stage in the life
    cycle of a star.
  • The Orion Nebula was the birthplace of these
    protostars.

46
27.3 The life cycle of stars
  • A star is born when temperature and pressure at
    its center become great enough to start nuclear
    fusion.

47
27.3 The life cycle of stars
  • A star is born when temperature and pressure at
    its center become great enough to start nuclear
    fusion.
  • Once nuclear fusion begins, a star is in the main
    sequence stage of its life cycle.

48
27.3 The life cycle of stars
  • The time a star stays on the main sequence
    depends on the stars mass.

49
27.3 The life cycle of stars
  • The time a star stays on the main sequence
    depends on the stars mass.
  • High-mass stars burn brighter, and hotter, using
    up their hydrogen faster than low-mass stars.

50
27.2 The old age of Sun-like stars
  • With no more energy flowing outward, nothing
    prevents gravity from crushing the matter in the
    core together.

51
27.2 The old age of Sun-like stars
  • With no more energy flowing outward, nothing
    prevents gravity from crushing the matter in the
    core together.
  • When hydrogen fusion stops, the core glows
    brightly and is called a white dwarf.

52
27.2 The old age of Sun-like stars
  • A planetary nebula forms when a star blows off
    its outer layers leaving its bare core exposed as
    white dwarf.

53
27.2 The old age of Sun-like stars
  • A planetary nebula forms when a star blows off
    its outer layers leaving its bare core exposed as
    white dwarf.
  • Planetary nebulae are one of natures ways of
    recycling the matter in old stars and
    distributing new elements.

54
27.3 Supernovae and synthesis of the elements
  • Scientists believe the early universe was mostly
    hydrogen, helium and a trace of lithium.

55
27.3 Supernovae and synthesis of the elements
  • Scientists believe the early universe was mostly
    hydrogen, helium and a trace of lithium.
  • Heavier elements are created by nuclear fusion
    inside the cores of stars.

56
27.3 Supernovae and synthesis of the elements
  • Scientists believe the early universe was mostly
    hydrogen, helium and a trace of lithium.
  • Heavier elements are created by nuclear fusion
    inside the cores of stars.
  • Nuclear fusion reactions are exothermic,
    releasing energy only up to iron.

57
27.3 Supernovae and synthesis of the elements
  • Scientists believe the early universe was mostly
    hydrogen, helium and a trace of lithium.
  • Heavier elements are created by nuclear fusion
    inside the cores of stars.
  • Nuclear fusion reactions are exothermic,
    releasing energy only up to iron.
  • When the core of the star contains mostly iron,
    nuclear fusion stops.

58
27.3 Supernovae and synthesis of the elements
  • If a stars iron core reaches 1.4 times the mass
    of the Sun, gravity becomes strong enough to
    combine electrons and protons into neutrons.

59
27.3 Supernovae and synthesis of the elements
  • If a stars iron core reaches 1.4 times the mass
    of the Sun, gravity becomes strong enough to
    combine electrons and protons into neutrons.
  • During this brief period, heavier elements such
    as gold and uranium are created, as atomic nuclei
    are smashed together.

60
27.3 Supernovae and synthesis of the elements
  • If a stars iron core reaches 1.4 times the mass
    of the Sun, gravity becomes strong enough to
    combine electrons and protons into neutrons.
  • During this brief period, heavier elements such
    as gold and uranium are created, as atomic nuclei
    are smashed together.
  • The core of the star collapses and the result is
    a spectacular explosion called a supernova.

61
27.3 Supernovae and synthesis of the elements
  • The Crab nebula is the remains of a supernova.

62
27.3 Supernovae and synthesis of the elements
  • The Crab nebula is the remains of a supernova.
  • Chinese astronomers recorded its demise 1054 AD.

63
27.3 Examining light from stars
  • Spectroscopy is a tool of astronomy in which the
    light produced by a star or other object (called
    its spectrum) is analyzed.

64
27.3 Analyzing light from stars
  • A spectrometer splits light into a spectrum of
    colors and displays lines of different colors
    along a scale.

65
27.3 Analyzing light from stars
  • A spectrometer splits light into a spectrum of
    colors and displays lines of different colors
    along a scale.
  • Each element has its own unique pattern of
    spectral lines.

66
27.2 Analyzing light from stars
  • In 1861, Sir William Huggins used spectroscopy to
    determine that the Sun and the stars are made
    mostly of hydrogen.

67
27.2 Analyzing light from stars
  • A few years later, Sir Joseph Norman Lockyer
    observed a line at the exact wavelength of 587.6
    nm.
  • He concluded that this must be an undiscovered
    element and named it helium, after the Greek name
    for the Sun, Helios.

68
27.2 Analyzing light from stars
  • A few years later, Sir Joseph Norman Lockyer
    observed a line at the exact wavelength of 587.6
    nm.

69
27.2 Analyzing light from stars
  • A few years later, Sir Joseph Norman Lockyer
    observed a line at the exact wavelength of 587.6
    nm.
  • He concluded that this must be an undiscovered
    element and named it helium, after the Greek name
    for the Sun, Helios.
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