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TEACHER RESOURCE PAGE
Answer Key
33.
34.
35.
36.
within 1,000 light-years of Earth
A
B
the brightness of a star as it appears to us on
Earth
37. the true brightness that a star would have if
all the stars were at a standard, uniform
distance from Earth
Directed Reading
SECTION: CHARACTERISTICS OF
STARS
1. a ball of gases that gives off a tremendous
amount of electromagnetic energy
2. From Earth, stars appear as tiny specs of
white light, but they actually vary in color.
3. B
4. A
5. C
6. D
7. C
8. A
9. the elements that make up the star
10. hydrogen; helium
11. A
12. C
13. B
14. the surface temperature of the star
15. 2,800 C to 24,000 C
16. red
17. blue
18. A
19. C
20. B
21. D
22. B
23. C
24. B
25. They move across the sky; they may revolve
around another star; they either move away
from or toward our solar system.
26. the apparent shift in the wavelength of light
emitted by a light source moving toward or
away from an observer
27. that those galaxies are moving away from
Earth
28. A
29. D
30. A
31. B
32. Parallax is the apparent shift in a star’s
position when viewed from different
locations. Scientists measure parallax to
determine a relatively close star’s distance
from Earth.
Directed Reading
SECTION: STELLAR EVOLUTION
1. B
2. the total amount of energy a star gives off
each second
3. the graph that illustrates the pattern revealed
when the surface temperatures of stars are
plotted against their luminosity
4. The temperature of a star’s surface is plotted
on the horizontal axis; the luminosity is
plotted on the vertical axis.
5. It is the band that runs diagonally through
the H-R diagram and extends from cool,
dim, red stars at the lower right to hot,
bright, blue stars at the upper left.
6. A
7. C
8. Dense regions of matter build up within the
nebula.
9. a shrinking, spinning region that begins to
flatten into a disk with a central
concentration of matter
10. Gravitational energy is converted into heat
energy, and the temperature of the protostar
increases.
11. It marks the birth of a star.
12. The rate of fusion increases.
13. It makes the star stable in size.
14. as long as it has an ample supply of
hydrogen to fuse into helium
15. C
16. B
17. when about 20% of the hydrogen atoms in
its core have fused into helium atoms
Original content Copyright © Holt McDougal. All rights reserved. Additions and changes to the original content are the responsibility of the instructor.
Holt McDougal Earth Science
69
Stars, Galaxies, and the Universe
TEACHER RESOURCE PAGE
18. As the helium core becomes hotter, it
transfers energy into a thin shell of hydrogen
surrounding the core.
19. They are large, bright, red stars. They are
above the main sequence on the H-R
diagram.
20. bright main-sequence stars that are more
massive than the sun and become larger than
regular giant stars
21. A
22. C
23. A
24. D
25. A
26. A supernova is a star that has such a
tremendous explosion that it blows itself
apart. Unlike a nova, a white dwarf can
sometimes accumulate so much mass on its
surface that gravity overwhelms the outward
pressure. The star collapses and is so dense
that the outer layers rebound and explode.
27. C
28. D
29. The core begins to collapse under its own
gravity, and it explodes.
30. a small but extremely dense ball of neutrons
left after a supernova explodes
31. a neutron star that emits a beam of radio
waves that sweep across space
32. If the leftover core of a star contains more
than 3 times the mass of the sun, the star
may contract more under its greater gravity
until the force crushes the dense core and
leaves a black hole.
33. because they do not give off light
Original content Copyright © Holt McDougal. All rights reserved. Additions and changes to the original content are the responsibility of the instructor.
Holt McDougal Earth Science
70
Stars, Galaxies, and the Universe