Download PP Chapter 28 Text

Hewitt/Lyons/Suchocki/Yeh
Conceptual Integrated
Science
Chapter 28
THE UNIVERSE
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This lecture will help you
understand:
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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
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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.
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Observing the Night Sky
The monthly constellations seen in the night
sky change as Earth’s path around the Sun
progresses.
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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?
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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.
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Observing the Night Sky
The seven stars of the Big Dipper are at
very different distances from Earth.
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Observing the Night Sky
A time-exposure of the night sky shows
streaks of stars from our “carousel Earth.”
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Observing the Night Sky
CHECK YOUR NEIGHBOR
Knowing the names of the constellations tells us much
about the
A.
B.
C.
D.
stars that comprise them.
people in the cultures that named them.
difference between stars and planets.
all of the above.
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Observing the Night Sky
CHECK YOUR ANSWER
Knowing the names of the constellations tells us much
about the
A.
B.
C.
D.
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.
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The Brightness and Colors
of 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)
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The Brightness and Colors of Stars
CHECK YOUR NEIGHBOR
Which of these stars radiates light of the longest
wavelength?
A.
B.
C.
D.
Red star.
Yellow star.
Blue star.
Violet star.
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The Brightness and Colors of Stars
CHECK YOUR ANSWER
Which of these stars radiates light of the longest
wavelength?
A.
B.
C.
D.
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.)
Copyright © 2007 Pearson Education, Inc., publishing as Pearson Addison-Wesley
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.
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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.
B.
C.
D.
the same.
half as much.
one quarter as much.
four times as much.
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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.
B.
C.
D.
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.
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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.
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The Hertzsprung-Russell Diagram
CHECK YOUR NEIGHBOR
On the H-R diagram, the Sun is
A.
B.
C.
D.
an average star.
seen to be special.
a low-temperature star.
especially bright.
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The Hertzsprung-Russell Diagram
CHECK YOUR ANSWER
On the H-R diagram, the Sun is
A.
B.
C.
D.
an average star.
seen to be special.
a low-temperature star.
especially bright.
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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.
B.
C.
D.
Lower left.
Upper left.
Lower right.
Upper right.
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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.
B.
C.
D.
Lower left.
Upper left.
Lower right.
Upper right.
Explanation:
Such a star would be a white dwarf.
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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.
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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)
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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
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The Life Cycles of Stars
CHECK YOUR NEIGHBOR
The source of energy in the Sun and stars is
A.
B.
C.
D.
chemical reactions.
thermonuclear reactions.
both of the above.
none of the above.
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The Life Cycles of Stars
CHECK YOUR ANSWER
The source of energy in the Sun and stars is
A.
B.
C.
D.
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.
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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
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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)
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Black Holes
CHECK YOUR NEIGHBOR
When a star collapses to one-tenth size, gravitation at its
surface becomes
A.
B.
C.
D.
one tenth as much.
the same.
10 times as much.
100 times as much.
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Black Holes
CHECK YOUR ANSWER
When a star collapses to one-tenth size, gravitation at its
surface becomes
A.
B.
C.
D.
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.
Copyright © 2007 Pearson Education, Inc., publishing as Pearson Addison-Wesley
Black Holes
CHECK YOUR NEIGHBOR
When a giant star collapses to become a black hole, gravity
is greatly increased
A.
B.
C.
D.
at it surface.
at its center.
in all surrounding space.
all of the above.
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Black Holes
CHECK YOUR ANSWER
When a giant star collapses to become a black hole, gravity
is greatly increased
A.
B.
C.
D.
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.
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Black Holes
CHECK YOUR NEIGHBOR
If the Sun collapsed to become a black hole, the orbit of
Earth would
A.
B.
C.
D.
remain unchanged.
be pulled inward toward the black hole.
spiral outward away from the black hole.
be a straight-line path.
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Black Holes
CHECK YOUR ANSWER
If the Sun collapsed to become a black hole, the orbit of
Earth would
A.
B.
C.
D.
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!
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Galaxies
Galaxy:
• A huge assemblage of stars, interstellar
gas, and dust
• Most familiar—Milky Way
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Galaxies
Three types of galaxies:
• Elliptical
• Irregular
• Spiral
This is a giant elliptical galaxy M87.
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Galaxies
A pair of irregular galaxies—
the Large Magellanic Cloud and
neighboring Small Magellanic Cloud.
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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!
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Galaxies
CHECK YOUR NEIGHBOR
The most common galaxies are
A.
B.
C.
D.
elliptical galaxies.
irregular galaxies.
spiral galaxies.
clusters of galaxies.
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Galaxies
CHECK YOUR ANSWER
The most common galaxies are
A.
B.
C.
D.
elliptical galaxies.
irregular galaxies.
spiral galaxies.
clusters of galaxies.
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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
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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
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The Big Bang
CHECK YOUR NEIGHBOR
Scientific evidence supports the date of the Big Bang event
at
A.
B.
C.
D.
7000 years ago.
100,000 years ago.
5 billion years ago.
13.7 billion years ago.
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The Big Bang
CHECK YOUR ANSWER
Scientific evidence supports the date of the Big Bang event
at
A.
B.
C.
D.
7000 years ago.
100,000 years ago.
5 billion years ago.
13.7 billion years ago.
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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
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Quasars
CHECK YOUR NEIGHBOR
When we speak of a quasar, we are talking about
A.
B.
C.
D.
the Big Bang.
a black hole.
a neutron star.
none of the above.
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Quasars
CHECK YOUR ANSWER
When we speak of a quasar, we are talking about
A.
B.
C.
D.
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.
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