Transcript Chapter 20 Notes

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Visual Concepts
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Chapter 20
The Universe
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
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Chapter 20
Section 1 The Life and Death of
Stars
Objectives
• Describe the basic structure and properties of stars.
• Explain how the surface temperature of a star is
measured.
• Recognize that all normal stars are powered by
fusion reactions that form elements.
• Identify the stages in the evolution of stars.
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Chapter 20
Section 1 The Life and Death of
Stars
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.
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Chapter 20
Section 1 The Life and Death of
Stars
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.
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Chapter 20
Section 1 The Life and Death of
Stars
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.
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Chapter 20
Section 1 The Life and Death of
Stars
Constellation
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Chapter 20
Section 1 The Life and Death of
Stars
Nuclear Fusion
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Chapter 20
Section 1 The Life and Death of
Stars
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.
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Chapter 20
Section 1 The Life and Death of
Stars
Structure of the Sun
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Chapter 20
Section 1 The Life and Death of
Stars
Structure of the Sun
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Chapter 20
Section 1 The Life and Death of
Stars
The Sun’s Atmosphere
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Chapter 20
Section 1 The Life and Death of
Stars
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.
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Chapter 20
Section 1 The Life and Death of
Stars
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.
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Chapter 20
Section 1 The Life and Death of
Stars
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.)
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Chapter 20
Section 1 The Life and Death of
Stars
Starlight Intensity Graph
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Chapter 20
Section 1 The Life and Death of
Stars
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.
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Chapter 20
Section 1 The Life and Death of
Stars
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.
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Chapter 20
Section 1 The Life and Death of
Stars
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.
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Chapter 20
Section 1 The Life and Death of
Stars
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.
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Chapter 20
Section 1 The Life and Death of
Stars
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
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Section 1 The Life and Death of
Stars
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.
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Section 1 The Life and Death of
Stars
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
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Chapter 20
Section 1 The Life and Death of
Stars
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.
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Chapter 20
Section 1 The Life and Death of
Stars
H-R Diagram
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Chapter 20
Section 1 The Life and Death of
Stars
Types of Stars
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Chapter 20
Section 2 The Milky Way and
Other Galaxies
Objectives
• Define galaxy, and identify Earth’s home galaxy.
• Describe two characteristics of a spiral galaxy.
• Distinguish between the three types of galaxies.
• Describe two aspects of a quasar, and identify the
tools scientists use to study quasars.
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Chapter 20
Section 2 The Milky Way and
Other Galaxies
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?
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Chapter 20
Section 2 The Milky Way and
Other Galaxies
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?
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Chapter 20
Section 2 The Milky Way and
Other Galaxies
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.
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Chapter 20
Section 2 The Milky Way and
Other Galaxies
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.
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Chapter 20
Section 2 The Milky Way and
Other Galaxies
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.
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Chapter 20
Section 2 The Milky Way and
Other Galaxies
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.
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Chapter 20
Section 2 The Milky Way and
Other Galaxies
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.
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Chapter 20
Section 2 The Milky Way and
Other Galaxies
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.
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Chapter 20
Section 2 The Milky Way and
Other Galaxies
Investigating Different Types of Galaxies
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Chapter 20
Section 2 The Milky Way and
Other Galaxies
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.
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Chapter 20
Section 2 The Milky Way and
Other Galaxies
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.
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Chapter 20
Section 2 The Milky Way and
Other Galaxies
Formation of the Solar System
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Chapter 20
Section 2 The Milky Way and
Other Galaxies
Lunar Phases
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Chapter 20
Section 2 The Milky Way and
Other Galaxies
Solar and Lunar Eclipses
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Chapter 20
Section 3 Origin of the Universe
Objectives
• Describe the basic structure of the universe.
• Describe red shift, and explain what it tells scientists
about our universe.
• State the main features of the big bang theory, and
explain the evidence supporting the expansion of the
universe.
• Explain how scientists are using tools and models to
hypothesize what may happen to the universe in the
future.
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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?
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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?
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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.
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Chapter 20
Section 3 Origin of the Universe
Cosmology
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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.
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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
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Chapter 20
Section 3 Origin of the Universe
Red Shift
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Section 3 Origin of the Universe
What Happened at the Beginning? continued
• Expansion implies that the universe was once
smaller.
• Long ago, the entire universe might have been
contained in an extremely small space.
• All of the matter in the universe appears to expand
rapidly outward, like a gigantic explosion
• Scientists call this hypothetical explosion the big
bang.
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Chapter 20
Section 3 Origin of the Universe
Universal Expansion
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Chapter 20
Section 3 Origin of the Universe
What Happened at the Beginning? continued
• Did the universe start with a big bang?
• Scientists have proposed several different theories to
explain the expansion of the universe.
• The most complete and widely accepted theory is the big
bang theory.
• Big bang theory the theory that all matter and
energy in the universe was compressed into an
extremely small volume that 10 to 20 billion years
ago exploded and began expanding in all
directions
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Chapter 20
Section 3 Origin of the Universe
Big Bang Theory
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Chapter 20
Section 3 Origin of the Universe
What Happened at the Beginning? continued
• Cosmic background radiation supports the big bang
theory.
• Cosmic background radiation is a steady but very
dim signal from all over the sky in the form of
radiation at microwave wavelengths.
• Many scientists believe that the microwaves are
dim remnants of the radiation produced during the
big bang.
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Chapter 20
Section 3 Origin of the Universe
What Happened at the Beginning? continued
• Radiation dominated the early universe.
• According to the big bang theory, expansion
cooled the universe enough for matter such as
protons, neutrons, and electrons to form.
• Processes in stars lead to bigger atoms.
• Once hydrogen atoms formed, stars and
galaxies began to form, too.
• All elements other than hydrogen and helium
form in stars.
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Chapter 20
Section 3 Origin of the Universe
Predicting the Future of the Universe
•
The future of the universe is uncertain.
•
•
The universe is expanding, but the combined
gravity of all the mass in the universe is also
pulling the universe inward.
The competition between these forces leaves
three possibilities:
1. The universe will keep expanding forever
2. The expansion of the universe will gradually slow
down, and the universe will approach a limit in size.
3. The universe will stop expanding and start to fall
back in on itself
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Chapter 20
Section 3 Origin of the Universe
Predicting the Future of the Universe,
continued
• The fate of the universe depends on mass.
• If there is not enough mass, the gravitational pull
will be too small to stop the expansion.
• If there is just the right amount of mass, the
expansion will continually slow down, but will
never stop completely.
• If there is too much mass, gravity will eventually
overcome expansion and the universe will
contract.
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Chapter 20
Section 3 Origin of the Universe
Predicting the Future of the Universe,
continued
• New technology helps scientists test theories.
• Powerful telescopes and other sensitive
equipment help scientists study the universe.
• Scientists make observations to test theories and
develop new explanations.
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Chapter 20
Section 3 Origin of the Universe
Predicting the Future of the Universe,
continued
• There is a debate about dark matter.
• There is more matter in the universe than what is
visible.
• Scientists call this dark matter.
• Dark matter may be planets, black holes, or brown
dwarfs (starlike objects that lack enough mass to
begin fusion.)
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Chapter 20
Section 3 Origin of the Universe
Predicting the Future of the Universe,
continued
• Scientists use mathematics to build better models.
• Theories can be expressed in mathematical form.
• Mathematical models can be used to help test
theories that are not easily observed.
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Chapter 20
Section 3 Origin of the Universe
Contents of Galaxies
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Chapter 20
Section 3 Origin of the Universe
Structure of the Universe
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Chapter 20
Section 3 Origin of the Universe
Concept
Mapping
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Chapter 20
Standardized Test Prep
Understanding Concepts
1. Light travels 9.5 X 1015 meters in one year. Express
the distance between the sun and its nearest
neighbor, Alpha Centauri—4.1X1016 meters—in
terms of light years.
A.
B.
C.
D.
0.43
2.2
4.3
22.0
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Chapter 20
Standardized Test Prep
Understanding Concepts, continued
1. Light travels 9.5 X 1015 meters in one year. Express
the distance between the sun and its nearest
neighbor, Alpha Centauri—4.1X1016 meters—in
terms of light years.
A.
B.
C.
D.
0.43
2.2
4.3
22.0
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Chapter 20
Standardized Test Prep
Understanding Concepts, continued
2. Toward which end of the spectrum is the light of a
receding galaxy shifted?
F.
G.
H.
I.
blue
green
red
yellow
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Chapter 20
Standardized Test Prep
Understanding Concepts, continued
2. Toward which end of the spectrum is the light of a
receding galaxy shifted?
F.
G.
H.
I.
blue
green
red
yellow
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Chapter 20
Standardized Test Prep
Understanding Concepts, continued
3. A star, such as the sun, in the middle of the main
sequence, remains at equilibrium for billions of years
before it changes. What forces keep the star from
shrinking or expanding during that period?
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Chapter 20
Standardized Test Prep
Understanding Concepts, continued
3. A star, such as the sun, in the middle of the main
sequence, remains at equilibrium for billions of years
before it changes. What forces keep the star from
shrinking or expanding during that period?
Answer: The equilibrium is a result of the force of
gravity, which pulls material inward, and the energy
produced by fusion, which pushes material outward.
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Chapter 20
Standardized Test Prep
Reading Skills
When a very large star collapses, it can form a black
hole. Inside a black hole, mass is so dense that
even light cannot reach the escape velocity of its
gravitational field. A black hole with a mass ten times
as great as the sun would have a radius of only
about 30 kilometers. Matter that strikes a black hole
becomes part of its mass. Black holes are detected
by their gravitational effects on matter around them.
4. Why can black holes only be observed by their
effects and not by direct observation through a large
telescope?
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Chapter 20
Standardized Test Prep
Reading Skills, continued
4. [See previous slide for question.]
Answer: Because no light can escape from the black
hole, it cannot be directly observed. Direct
observation of a distant object can only be made by
collecting electromagnetic radiation that it emits or
reflects.
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Chapter 20
Standardized Test Prep
Interpreting Graphics
Base your answers to questions 5 through 8 on the
illustration below.
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Chapter 20
Standardized Test Prep
Interpreting Graphics, continued
5. Which of these stars is most likely to become a white
dwarf in the near future?
A.
B.
C.
D.
Betelgeuse
Sirius
Proxima Centauri
Alpha Centauri
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Chapter 20
Standardized Test Prep
Interpreting Graphics, continued
5. Which of these stars is most likely to become a white
dwarf in the near future?
A.
B.
C.
D.
Betelgeuse
Sirius
Proxima Centauri
Alpha Centauri
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Chapter 20
Standardized Test Prep
Interpreting Graphics, continued
6. Why does Sirius appear brighter in the night sky
than Betelgeuse?
F. Sirius is a brighter star than Betelgeuse.
G. Betelgeuse is farther from Earth than Sirius.
H. Betelgeuse is cooler than Sirius, so it does not
emit as much light.
I. Sirius has a smaller diameter, so it is a more
concentrated light source.
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Chapter 20
Standardized Test Prep
Interpreting Graphics, continued
6. Why does Sirius appear brighter in the night sky
than Betelgeuse?
F. Sirius is a brighter star than Betelgeuse.
G. Betelgeuse is farther from Earth than Sirius.
H. Betelgeuse is cooler than Sirius, so it does not
emit as much light.
I. Sirius has a smaller diameter, so it is a more
concentrated light source.
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Copyright © by Holt, Rinehart and Winston. All rights reserved.
Chapter 20
Standardized Test Prep
Interpreting Graphics, continued
7. Which type of star would more likely be found in the
arms of the Milky Way than in its core?
A.
B.
C.
D.
red giants
white dwarfs
green main sequence stars
yellow main sequence stars
Chapter menu
Resources
Copyright © by Holt, Rinehart and Winston. All rights reserved.
Chapter 20
Standardized Test Prep
Interpreting Graphics, continued
7. Which type of star would more likely be found in the
arms of the Milky Way than in its core?
A.
B.
C.
D.
red giants
white dwarfs
green main sequence stars
yellow main sequence stars
Chapter menu
Resources
Copyright © by Holt, Rinehart and Winston. All rights reserved.
Chapter 20
Standardized Test Prep
Interpreting Graphics, continued
8. Which of these stars would appear to be brightest if
all of them were observed from the same distance?
F.
G.
H.
I.
Aldebaran
Canopus
Sun
Vega
Chapter menu
Resources
Copyright © by Holt, Rinehart and Winston. All rights reserved.
Chapter 20
Standardized Test Prep
Interpreting Graphics, continued
8. Which of these stars would appear to be brightest if
all of them were observed from the same distance?
F.
G.
H.
I.
Aldebaran
Canopus
Sun
Vega
Chapter menu
Resources
Copyright © by Holt, Rinehart and Winston. All rights reserved.