1. The Universe Preview Understanding Concepts Reading Skills
Interpreting Graphics

2. Understanding Concepts
1. Inside a star’s core, hydrogen nuclei fuse to
form deuterons, which consist of one proton
and one neutron. When deuterons fuse with hydrogen nuclei, what do they form?
A. plasma
B. hydrogen atoms
C. hydrogen nuclei
D. helium nuclei

3. Understanding Concepts
1. Inside a star’s core, hydrogen nuclei fuse to
form deuterons, which consist of one proton
and one neutron. When deuterons fuse with hydrogen nuclei, what do they form?
A. plasma
B. hydrogen atoms
C. hydrogen nuclei
D. helium nuclei

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2. The hottest stars appear to be which color?
F. blue
G. green
H. red
I. yellow

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2. The hottest stars appear to be which color?
F. blue
G. green
H. red
I. yellow

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3. What is the final stage in the life cycle of most
stars in our galaxy?
A. red giant
B. white dwarf
C. nebula
D. supernova

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3. What is the final stage in the life cycle of most
stars in our galaxy?
A. red giant
B. white dwarf
C. nebula
D. supernova

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4. What objects are thought to be the most distant
objects in the universe?
F. spiral galaxies
G. elliptical galaxies
H. quasars
I. nebulas

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4. What objects are thought to be the most distant
objects in the universe?
F. spiral galaxies
G. elliptical galaxies
H. quasars
I. nebulas

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5. About how long does it take light from the sun
to reach Earth?
A. 8 seconds
B. 8 minutes
C. 8 days
D. 8 years

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5. About how long does it take light from the sun
to reach Earth?
A. 8 seconds
B. 8 minutes
C. 8 days
D. 8 years

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6. Why is the light from distant galaxies almost
always shifted toward the red end of the
spectrum?

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6. Why is the light from distant galaxies almost
always shifted toward the red end of the
spectrum?
Answer: They are moving away from us
(Doppler effect.)

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7. What is the name for the process in which
atoms combine to form larger atoms, and
where does it take place?

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7. What is the name for the process in which
atoms combine to form larger atoms, and
where does it take place?
Answer: Fusion, inside of stars

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8. If the Milky Way galaxy has a spiral shape, why
do we see it as a streak across the sky?

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8. If the Milky Way galaxy has a spiral shape, why
do we see it as a streak across the sky?
Answer: We are inside the Milky Way and can only see a side view.

18. Reading Skills AFTER THE BANG
Astronomers and physicists generally agree that the universe began about 13 billion to 15 billion years ago in the big bang. For some time after the big bang occurred, the universe was much hotter and denser than it is today. In fact, it was so hot and dense that there were no individual atoms; instead, subatomic particles, including protons, neutrons, and photons (particles of pure energy) made a dense fluid called plasma. Every time that a proton and an electron combined, drawn together by their opposite charges, a photon collided with them and ripped them apart again.

19. Reading Skills, continued
AFTER THE BANG, continued
After a few hundred thousand years, the average temperature of the plasma was low enough that the protons could hold onto their electrons to form neutral atoms, and photons could escape without being absorbed.

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9. Why couldn’t stable atoms form before the
cooling of the superheated plasma?
F. Protons and electrons were moving too
fast to combine.
G. Before the plasma cooled, subatomic particles
carried no charge and therefore were not attracted to one another.
H. Colliding with photons caused immediate
destruction of any atom that formed.
I. Cosmic background radiation prevented
the atoms from forming.

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9. Why couldn’t stable atoms form before the
cooling of the superheated plasma?
F. Protons and electrons were moving too
fast to combine.
G. Before the plasma cooled, subatomic particles
carried no charge and therefore were not attracted to one another.
H. Colliding with photons caused immediate
destruction of any atom that formed.
I. Cosmic background radiation prevented
the atoms from forming.

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10. Telescopes show images based on the photons
they receive, in the form of light, radio waves,
or other radiation. They show us events of the
past, because photons take time to travel to us
from those events. Why would it be difficult for
telescopes to observe events that took place
before the cooling of the superheated plasma?

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10. Telescopes show images based on the photons
they receive, in the form of light, radio waves,
or other radiation. They show us events of the
past, because photons take time to travel to us
from those events. Why would it be difficult for
telescopes to observe events that took place
before the cooling of the superheated plasma?
Answer: No photons escaped.

24. Interpreting Graphics
The following chart shows the fusion reactions in a large-mass star,
which create elements that are heavier than those found in stars like
the sun. Use this diagram to answer questions 11 and 12.

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11. Which element fuses to become oxygen?
A. carbon
B. neon
C. silicon
D. iron

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11. Which element fuses to become oxygen?
A. carbon
B. neon
C. silicon
D. iron

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12. Do the elements that are produced by fusion get heavier or lighter as they get closer to the center of the large-mass star? Why?

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12. Do the elements that are produced by fusion get heavier or lighter as they get closer to the center of the large-mass star? Why?
Answer: Heavier; the pressure of gravity.

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Astronomers have determined that black holes, with masses from a
few million to a billion times greater than the mass of our sun, reside in
the centers of nearby galaxies. The graphic shows the relationship
between the mass of black holes and the size of the bulge of stars at the
center of these galaxies. Use the graphic to answer questions 13 and 14.

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13. How does the mass of the black hole at the center of a galaxy relate to the mass of the bulge
of stars that surround the black hole?
F. The two masses are always equal.
G The two masses are directly proportional.
H. The two masses are inversely proportional.
I. The two masses are unrelated to one another.

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13. How does the mass of the black hole at the center of a galaxy relate to the mass of the bulge
of stars that surround the black hole?
F. The two masses are always equal.
G The two masses are directly proportional.
H. The two masses are inversely proportional.
I. The two masses are unrelated to one another.

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14. Why would a black hole be surrounded by a bulge of stars?

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14. Why would a black hole be surrounded by a bulge of stars?
Answer: The gravitational pull of the black hole’s enormous mass causes stars to move toward it.