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C H A P T E R
2
THE SKY
GUIDEPOSTS
2-1 The Stars
How do astronomers refer to stars?
Astronomers divide the sky into 88 constellations. Although the constellations originated in Greek
and Middle Eastern mythology, the names are Latin. Even the modern constellations, added to fill
in the spaces between the ancient figures, have Latin names.
The names of stars usually come from ancient Arabic, although modern astronomers often refer to a
star by its constellation and a Greek letter assigned according to its brightness within the
constellation.
How can you compare the brightness of the stars?
The magnitude system is the astronomer’s brightness scale. First-magnitude stars are brighter than
second-magnitude stars, which are brighter than third-magnitude stars, and so on. The magnitude
you see when you look at a star in the sky is its apparent visual magnitude, which does not take into
account its distance form Earth.
Apparent visual magnitude, mv, includes only the light that human eyes can see.
2-2 The Sky and its Motion
How does the sky move as Earth moves?
The celestial sphere is a model of the sky, carrying the celestial objects around Earth. Because
Earth rotates eastward, the celestial sphere appears to rotate westward on its axis. The northern and
southern celestial poles are the pivots on which the sky appears to rotate.
The celestial equator, an imaginary line around the sky above Earth’s equator, divides the sky in
half.
Astronomers often refer to angles “on” the sky as if the stars, sun, moon, and planets were
equivalent to spots painted on a plaster ceiling. These angular distances are unrelated to the true
distance between the objects in light-years.
What you see of the celestial sphere depends on your latitude. Much of the southern hemisphere of
the sky is not visible from northern Latitudes. To see that part of the sky, you would have to travel
southward over Earth’s surface.
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The angular distance from the horizon to the north celestial pole always equals your latitude. This is
the basis for celestial navigation.
The gravitational forces of the moon and sun act on the spinning Earth and cause it to precess like a
top. Earth’s axis of rotation sweeps around in a conical motion with a period of 26,000 years, and
consequently, the celestial poles and celestial equator move slowly against the background of the
stars.
2-3 The Cycles of the Sun
What causes the seasons?
Because Earth orbits the sun, the sun appears to move eastward along the ecliptic through the
constellations. It circles the entire zodiac in a year.
Because the ecliptic is tipped 23.5 to the celestial equator, the sun spends half the year in the
northern celestial hemisphere and half in the southern celestial hemisphere.
In the summer, the sun is above the horizon longer and shines more directly down on the ground.
Both effects cause warmer weather.
2-4 The Motion of the Planets
In addition to the sun, the visible planets also move along the ecliptic, and their positions give rise to
the ancient superstition called astrology.
Mercury and Venus follow orbits inside Earth’s orbit and never move far from the sun. They are
visible in the east before dawn or in the west after sunset.
How do astronomical cycles affect Earth’s climate?
Changes in the shape of Earth’s orbit, in its precession, and in its axial tilt can alter the planet’s heat
balance and seem to be at least partly responsible for the ice ages and glacial periods.
CHAPTER OUTLINE
Guideposts
2-1 The Stars
Constellations
The Names of the Stars
The Brightness of Stars
Magnitude and Intensity
Window on Science 2-1
Scientific Arguments: The Structure of Science
Building Scientific Arguments
2-2 The Sky and Its Motion
Window on Science 2-2
Frameworks for Thinking about Nature: Scientific Models
The Celestial Sphere
Precession
Concept Page: The Sky Around Us
Building Scientific Arguments
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2-3
2-4
2-5
Window on Science 2-3
Naming Versus Understanding: The True Goal of Science
The Cycles of the Sun
The Annual Motion of the Sun
The Seasons
Building Scientific Arguments
The Motions of the Planets
The Moving Planets
Concept Page: The Cycle of the Seasons
Astrology
Window on Science 2-4
Astrology and Pseudoscience
Building Scientific Arguments
Astronomical Influences on Earth's Climate
The Hypothesis
The Evidence
Window on Science 2-5
The Foundation of Science: Evidence
EDUCATIONAL RESOURCES
 Web Resources and CD-ROMs in the Media Cluster
Ace Astronomy (http:/ace.brookscole.com/sf9 selecting Chapter 2) and TheSky software with this text have
activities that can be used to improve understanding of the concepts of this chapter (see the ``Ace
Astronomy” and “Exploring The Sky” activities at the end of the chapter ).
Other internet sites related to this material:
http://skyandtelescope.com/
http://einstein.stcloudstate.edu/Dome/
http://einstein.stcloudstate.edu/Dome/constellns/constlist.html
http://earthobservatory.nasa.gov/Library/Giants/Milankovitch/
Lists events in the night sky
Online night sky with constellations
Greek Constellation Mythology
Milankovitch & his theory
ANSWERS TO REVIEW QUESTIONS
1.
Our current scientific culture has been greatly influenced by Western Civilization, and the modern
constellations came about as Europeans began to explore the world during the 15th to the 17th centuries.
The southern sky was unknown by the ancient Greeks and hence uncharted until the age of exploration
began. European explorers created constellations in the southern hemisphere that depicted various
devices of their time. Europeans also created a few northern hemisphere constellations. Because most
of the bright stars were already part of ancient constellations, these newly created northern hemisphere
constellations were developed using faint stars.
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2.
The Greek letter indicates its brightness relative to the other stars in the constellation. The brighter stars
have Greek letters nearer the beginning of the Greek alphabet. The Arabic name contains no information
concerning brightness of the star.
3.
a)  Ursa Majoris is the brighter of the two because it has a Greek letter designation that suggests that it
is the brightest star in the constellation of Ursa Majoris.
b) It is difficult to determine which is brighter; one might guess that  Pegasi should be brighter than 
Scorpii. Both constellations are bright constellations, and  is one of the brighter stars in Pegasus, while
 would be one of the moderately bright stars in Scorpius. As it turns out,  Scorpii is twice as bright as
 Pegasi.
c)  Orionis should be much brighter than  Telescopii. Orion is a very bright constellation with
several stars brighter than second magnitude. On the other hand, Telescopium is a faint constellation
with no stars brighter than third magnitude. (Note:  Telescopii doesn't exist! The star originally listed
as  Telescopii is actually the star  Sagittarii).
4.
The magnitude scale is confusing because it is an inverse scale, meaning that bright objects have smaller
magnitudes than fainter objects. Additionally, the scale is logarithmic and not linear. That is, one star
that is two times brighter than another does not have two times (or half) the magnitude of the other.
Instead they will differ in magnitude by less than one.
5.
The celestial sphere is convenient, especially for pointing telescopes. When pointing a telescope at an
object, we only need to know the direction to the object, not how far away it is. It also adequately
represents what we see when we look at the night sky.
6.
The celestial pole is a point on the celestial sphere where a line from the center of Earth through one of
the geographic poles would intersect the celestial sphere. The celestial equator is the line around the
celestial sphere that is everywhere 90° from each of the celestial poles.
7.
The north celestial pole is not visible from any latitude south of the equator. The south celestial pole is
not visible from any latitude north of the celestial equator. However, the celestial equator is always
visible. When the observer is either at the north or south geographic pole, the celestial equator will
coincide with the horizon (if we neglect atmospheric refraction).
8.
If we mean Earth does not turn on its axis with respect to the stars, then defining an ecliptic would be
possible, but it would mean using observations from many different locations on Earth. In this case,
defining latitude could get a little tricky since there would be no pole star.
If we mean that Earth does not rotate with respect to the sun (i.e., Earth being in synchronous rotation
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with the sun), it would be possible but again would require coordinated observations between the light
side and dark side. Celestial poles and an equator could be defined under these circumstances.
9.
During the winter, light from the sun hits Earth at a more oblique angle than it does during the summer.
The length of time that the sun is above the horizon is noticeably shorter during the winter than during
the summer.
10. First the seasons are reversed. The season when the sun is highest in the sky at noon in the Southern
Hemisphere is the season when the sun is lowest in the Northern Hemisphere. Due to the eccentricity of
Earth's orbit with perihelion occurring in early January, the Southern Hemisphere summers should be
slightly warmer than Northern Hemisphere summers because Earth is slightly closer to the sun during the
Southern Hemisphere summer. For the same reason the Southern Hemisphere winters should be slightly
warmer than the Northern Hemisphere winters.
11. During winter in the Northern Hemisphere, Earth is closer to the sun than it is during winter in the
Southern Hemisphere. When Earth is closer to the sun, the length of the solar day is greater than
average. Since the Northern Hemisphere daylight would be a little longer, and the sun would be a little
closer, the Northern Hemisphere winters should be a little warmer on average.
12. The constellation looks odd in its positioning relative to the horizon because the stamp depicts the sky as
seen from the southern hemisphere. Orion is on the celestial equator. Considering the extreme case,
compared to an observer at the north geographic pole, an observer at the south geographic pole will see
Orion as “up side down” since the two observers are inverted relative to one another. Try making a
drawing to see this. For northern and southern hemisphere observers not at the poles, the situation is
similar (but less extreme) and results in differing views of Orion.
ANSWERS TO DISCUSSION QUESTIONS
1.
These concepts are listed in the common order of progressively better understanding. Even astronomers
sometimes unconsciously switch to the earlier, less realistic concepts in discussion.
2.
In the case of 90 degrees, the seasons would be much more extreme with much larger temperature and
daylight variation during the year. For zero degrees, the seasons would be eliminated (at least variations
due to tilt relative to the sun).
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ANSWERS TO PROBLEMS
1.
Approximately 2 magnitudes smaller
2.
Approximately 4
3.
630
4.
2800
5.
A is brighter than B by a factor of 6.3.
6.
A is brighter than B by a factor of 170.
7.
The sun is 400,000 times brighter than the full moon.
8.
66.5°; 113.5°
9.
The angle between the north celestial pole and the northern horizon is equal to your latitude.
The angle between the southern horizon and the noon sun at the summer solstice is given by , where
  ( 90   lat .)  23. 5 .
This equation assumes that you are located in the northern hemisphere.
The equation works equally well in the southern hemisphere if the southern latitudes are taken to be
negative.
For an observer at latitude 40° N, the angle between the southern horizon and the noon sun at the
summer solstice would be 73.5°. For an observer at latitude 40 S, the angle between the southern
horizon and the summer solstice sun at noon would be 153.5.
ANSWERS TO BUILDING SCIENTIFIC ARGUMENTS
1.
Even though it is awkward, astronomers continue to use the magnitude system after two millennia
because we can compare the magnitude of a star today with the magnitude determined many years ago.
Now, a large body of information exists in terms of magnitudes, so it is easiest if we continue to use the
system.
2.
A more exact improved definition of circumpolar constellations is a constellation that is located entirely
within an angular distance of a celestial pole equal to the observer's latitude. For an observer at
sufficiently high latitude, Ursa Major would be inside this circle. On the other hand, at lower latitude,
for Ursa Major, this would not be the case. At the Earth’s equator, no constellation would be
circumpolar. With this definition of a circumpolar constellation, Orion would not be a circumpolar
constellation for any observer because a portion of Orion is more than 90° away from the north celestial
pole, and another portion of Orion is more than 90° away from the south celestial pole. With this
definition, any constellation that extends across the celestial equator, as Orion does, could not be a
circumpolar constellation for any observer.
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This definition is as arbitrary as any other. We could clearly require that only 50% of the constellation
remain above the horizon, and then Orion would be circumpolar for nearly all observers.
3.
The ellipticity of Earth's orbit makes Northern Hemisphere winters slightly warmer than Southern
Hemisphere winters.
4.
If the planets' orbits all were in the same plane as Earth's orbit, then the planets would all appear exactly
on the ecliptic at all times. The most unique difference would be the frequent occurrence of occultations
of one planet by another planet. Retrograde motion would still be visible, but instead of a loop, each
planet would trace an exact reversal in direction moving back directly over its path.
5.
If Earth's orbit were circular, precession would have no effect on the seasons.
TEST QUESTIONS
MULTIPLE CHOICE
GUIDEPOST CATEGORY: How do astronomers refer to stars?
1.
In one way of naming stars, a ______________ letter indicates its brightness relative to the other stars in
the constellation.
*
2.
a.
English
b.
Arabic
c.
Greek
d.
Cyrillic
A constellation must consist of a number of stars, all
*
a.
at the same distance from the Earth.
b.
at various different distances from the Earth.
c.
within a boundary in the same general angular area of the sky.
d.
Wrong! Constellations are made of planets only.
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3.
Although the constellations originated in Greek and Middle Eastern mythology, the names are
*
4.
English.
b.
German.
c.
Russian.
d.
Chinese.
e.
Latin.
The names of stars usually come from
*
5.
a.
a.
ancient Arabic.
b.
ancient English.
c.
Latin.
d.
Russian.
e.
Chinese.
________________________is the brightest star in the constellation of Ursa Majoris.
*
a.
β Ursa Majoris
b.
γ Ursa Majoris
c.
α Ursa Majoris
d.
Wrong! Ursa Majoris is the name of the brightest star.
GUIDEPOST CATEGORY: How can you compare the brightness of the stars?
6.
The magnitude scale
*
a.
originated just after the telescope was invented.
b.
can be used to indicate the apparent intensity of a celestial object.
c.
is used to measure the temperature of a star.
d.. was used to determine the rate of precession.
7.
The apparent visual magnitude of a star is 7.3. This tells us that the star is
*
a.
one of the brighter stars in the sky.
b.
bright enough that it would be visible even during the day.
c.
not visible with the unaided eye.
e.
very close to Earth.
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8.
The apparent visual magnitude of a star is a measure of the star's
*
9.
a.
size.
b.
intensity.
c.
distance.
d.
color.
e.
temperature.
Which star in the table below would appear the brightest to an observer on Earth?
*
a.
 Cet
b.
 CMa
c.
Nim
d.
 Per
e.
 Dra
Star
Apparent Visual
Name
Magnitude
 Dra
3.07
 Cet
2.53
 Per
3.98
Nim
8.07
 CMa
-1.46
10. Based on the information in the table below, what is the ratio of the intensity of  Dra to that of Nim?
*
a.
2.512
b.
5
Star
Apparent Visual
c.
8.07
Name
Magnitude
d.
11.14
 Dra
3.07
e.
100
 Cet
2.53
 Per
3.98
Nim
8.07
 Cma
-1.46
11. Which star in the table below would not be visible to the unaided eye of an observer on Earth?
*
a.
 Cet
b.
 Cma
c.
Nim
d.
e.
Star
Apparent Visual
Name
Magnitude
 Per
 Dra
3.07
 Dra
 Cet
2.53
 Per
3.98
Nim
8.07
 Cma
-1.46
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12. The star Vega has an apparent visual magnitude of 0.03, and the star HR 4374 has an apparent visual
magnitude of 4.87. It has been determined that both stars are at the same distance from Earth. What does
this information tell us about the two stars?
*
a.
Vega must be closer to Earth than HR 4374.
b.
Vega must be farther from Earth than HR 4374.
c.
Vega must produce less energy than HR 4374.
d.
Vega must produce more energy than HR 4374.
e.
Vega will appear fainter to us than HR 4374.
13. Polaris is a second magnitude star, and Phi Pegasi is about 16 times fainter than Polaris. What is the
approximate magnitude of Phi Pegasi?
*
a.
18
b.
-14
c.
3
d.
-3
e.
5
14. Star A has an apparent visual magnitude of 13.4, and star B has an apparent visual magnitude of 15.4.
Star A is _________________ than star B.
*
a.
2 times fainter
b.
2 times brighter
c.
6.3 times fainter
d.
6.3 times brighter
e.
29.8 times fainter
GUIDEPOST CATEGORY: How does the sky move as the Earth moves?
15. Seen from the northern latitudes, the star Polaris
*
a.
is never above the horizon during the day.
b.
always sets directly in the west.
c.
is always above the northern horizon.
d.
is never visible during the winter.
e.
is the brightest star in the sky.
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16. An observer on Earth's equator would find
*
a.
Polaris directly overhead.
b.
Polaris 40° above the northern horizon.
c.
that the celestial equator coincides with the horizon.
d.
the celestial equator passing directly overhead.
e.
that the ecliptic coincides with the horizon.
17. The celestial equator is
*
a.
a line around the sky directly above Earth's equator.
b.
the dividing line between the north and south celestial hemispheres.
c.
the path that the sun appears to follow on the celestial sphere as Earth orbits the sun.
d.
a and b.
e.
a and c.
18. The ________ is the point on the celestial sphere directly above any observer.
*
a.
north celestial pole
b.
south celestial pole
c.
zenith
d.
celestial equator
e.
asterism
19. An observer in the Northern Hemisphere watches the sky for several hours. Due to the motion of Earth,
this observer notices that the stars near the north celestial pole appear to move
*
a.
counter clockwise.
b.
clockwise.
c.
from left to right.
d.
from right to left.
e.
nearly vertically upward.
20. You live at a latitude of 73° N. What is the angle between the northern horizon and the north celestial
pole?
*
a.
73°
b.
27°
c.
17°
d.
23½°
e.
5°
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21. You live at a latitude of 39° S. What is the angle between the southern horizon and the south celestial
pole?
*
a.
45°
b.
23.5°
c.
39°
d.
51°
e.
The answer depends on the day of the year.
22. You live at a latitude of 28° N. What is the angle between the northern horizon and the north celestial
pole?
*
a.
62°
b.
28°
c.
40°
d.
23½°
e.
5°
23. You live at a latitude of 16° S. What is the angle between the southern horizon and the south celestial
pole?
*
a.
74°
b.
164°
c.
16°
d.
23½°
e.
5°
24. You live at a latitude of 32° N. What is the angle between the southern horizon and the sun at noon at
the vernal equinox?
*
a.
45°
b.
23.5°
c.
32°
d.
58°
e.
81.5
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25. You live at a latitude of 61° N. What is the angle between the southern horizon and the sun at noon at
the summer solstice?
*
a.
52.5°
b.
23.5°
c.
61°
d.
29°
e.
5.5
26. You live at a latitude of 17° N. What is the angle between the southern horizon and the sun at noon at
the winter solstice?
*
a.
17°
b.
23.5°
c.
96.5°
d.
73°
e.
49.5
27. If the north celestial pole appears on your horizon, what is your latitude?
*
a.
90° N
b.
90° S
c.
0°
d.
45° N
e.
The latitude of the observer cannot be determined from the information given.
28. What is the approximate latitude of the observer in the diagram below?
*
a.
90° N
b.
90° S
c.
50° N
North
Celestial
Pole
E
N
d.
50° S
e.
0°
S
W
29. What is the approximate latitude of the observer in the diagram below?
*
a.
20° N
b.
20° S
c.
70° N
d.
70° S
e.
0°
E
N
South
Celestial
Pole
S
W
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30. An observer in the Northern Hemisphere takes a time exposure photograph of the night sky. If the
illustration depicts the photograph taken by the observer, which direction was the camera pointing?
*
a.
straight north
b.
straight east
c.
straight south
d.
straight west
e.
straight up, directly overhead
Star Trails
Horizon
31. An observer in the Northern Hemisphere takes a time exposure photograph of the night sky. If the
illustration depicts the photograph taken by the observer, which direction was the camera pointing?
a.
straight north
b.
straight east
c.
straight south
d.
straight west
e.
straight up, directly overhead
Star Trails
*
Horizon
32. An observer in the Southern Hemisphere takes a time exposure photograph of the night sky. If the
illustration depicts the photograph taken by the observer, which direction was the camera pointing?
*
a.
straight north
b.
straight east
c.
straight south
d.
straight west
e.
straight up, directly overhead
Star Trails
Horizon
33. An observer in the Southern Hemisphere takes a time exposure photograph of the night sky. If the
illustration depicts the photograph taken by the observer, which direction was the camera pointing?
*
a.
straight north
b.
straight east
c.
straight south
d.
straight west
e.
straight up, directly overhead
Star Trails
14
Horizon
Chapter 2
Seeds’ FOUNDATIONS OF ASTRONOMY Instructors Manual and Test Bank 9e
Revised by Gene Byrd
34. An observer in the Northern Hemisphere takes a time exposure photograph of the night sky. If the
illustration depicts the photograph taken by the observer, which direction was the camera pointing?
*
a.
straight north
b.
straight east
c.
straight south
d.
straight west
e.
straight up, directly overhead
Star Trails
Horizon
35. An observer in the Southern Hemisphere takes a time exposure photograph of the night sky. If the
illustration to the right depicts the photograph taken by the observer, which direction was the camera
pointing?
*
a.
straight north
b.
straight east
c.
straight south
d.
straight west
e.
straight up, directly overhead
Star Trails
Horizon
GUIDEPOST CATEGORY: What causes the seasons?
36. What causes summer here in the northern hemisphere? In the summer, at this point
*
a.
the Earth is closer to the sun.
b.
the Earth's northern hemisphere is tilted toward the sun.
c.
the Earth's northern hemisphere is tilted away from the sun.
37. When it is winter in the northern hemisphere, it is ________ in the southern hemisphere.
*
a.
winter
b.
summer
c.
spring
d.
fall
38. The sun moves ____________ along the ecliptic among the stars.
*
a.
eastward
b.
westward
c.
The sun does not appear to move.
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39. Which of the following causes seasons on the earth?
*
a.
the earth being closer to the sun during our summer and farther during our winter
b.
the sun's varying light output
c.
the tilt of the earth's axis
d.
the eleven-year sunspot cycle
40. The summer solstice (at the start of summer) is the point on the ecliptic where the sun
*
a.
crosses the celestial equator moving north.
b.
crosses the celestial equator moving south.
c.
is farthest north of the celestial equator halting its northward movement.
d.
is farthest south of the celestial equator halting its southward movement.
41. At the time of the winter solstice (the start of winter) the sun is
*
a.
farthest south of the celestial equator.
b.
farthest north of the celestial equator.
c.
on the celestial equator moving north.
d.
on the celestial equator moving south.
42. As seen from the earth, the sun appears to move ____________ along the ________ among the stars.
*
a.
eastward, celestial equator
b.
westward, celestial equator
c.
eastward, ecliptic
d.
westward, ecliptic
e.
Wrong! The sun does not appear to move among the stars.
43. At the time of the winter solstice (the start of winter) the sunlight is at a lower angle and thus is ______
than(as) in the start of summer.
*
a. less intense
b. more intense
c. the same intensity
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GUIDEPOST CATEGORY: How do astronomical cycles affect Earth’s climate?
44. Precession of the rotation axis of Earth is caused by
*
a.
the force of gravity from the sun and moon on Earth's equatorial bulge.
b.
the force of gravity from the sun and Jupiter on the Earth-moon system.
c.
the magnetic field of Earth.
d.
the formation and subsequent melting of glaciers during the ice-ages.
e.
the impact of asteroids.
45. Precession of the rotation axis of Earth takes _______________to complete a cycle.
*
a.
24 hours
b.
one year
c.
260 years
d.
26,000 years
e.
260,000 years
46. Precession of the rotation axis of Earth is caused by
*
a.
the force of gravity from the sun and moon on Earth's equatorial bulge.
b.
the force of gravity from the sun and Jupiter on the Earth-moon system.
c.
the magnetic field of Earth.
d.
the formation and subsequent melting of glaciers during the ice-ages.
e.
the impact of asteroids.
47. The inclination of the axis of the earth varies from 22° to 24° degrees taking __________ to complete a
cycle.
*
a.
24 hours
b.
1 year
c.
499 years
d.
41,000 years
e.
Wrong! The Earth’s axis tilt is fixed at 23.50.
48. Precession of the rotation axis of Earth takes _______________to complete a cycle.
*
a.
24 hours
b.
one year
c.
260 years
d.
26,000 years
e.
260,000 years
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Chapter 2
Seeds’ FOUNDATIONS OF ASTRONOMY Instructors Manual and Test Bank 9e
Revised by Gene Byrd
49. The elliptical shape of the Earth’s orbit varies with time and takes _______________to complete a
cycle.
*
a.
24 hours
b.
one year
c.
260 years
d.
26,000 years
e.
100,000 years
50. In the Milankovitch theory, the elliptical shape of the Earth’s orbit, its axis tilt, and axis precession vary
with time. These combined at times to create ____________ on Earth.
*
a.
day and night
b.
seasonal temperature variations
c.
daily temperature variations
d.
ice ages
e.
the constellations
TRUE/FALSE
GUIDEPOST CATEGORY: How do astronomers refer to stars?
F
1.
The Greeks created the constellations.
GUIDEPOST CATEGORY: How can you compare the brightness of the stars?
T
2.
A second magnitude star in Ursa Major is brighter than a fourth magnitude star in Orion.
T
3.
The Greek letter designation conveys information about a star's location and brightness.
F
4.
Hipparchus devised the magnitude system in the late 1700’s.
GUIDEPOST CATEGORY: How does the sky move as the Earth moves?
T
5.
The moon and visible planets are always within a few degrees of the ecliptic.
F
6.
Polaris has always been the star nearest the north celestial pole.
F
7.
The celestial equator always passes directly overhead.
T
8.
The celestial equator always crosses the horizon at the east point and west point.
T
9.
Navigators can find their latitude by measuring the angle from the northern horizon to the north
celestial pole.
18
Chapter 2
Seeds’ FOUNDATIONS OF ASTRONOMY Instructors Manual and Test Bank 9e
Revised by Gene Byrd
GUIDEPOST CATEGORY: How do astronomical cycles affect Earth’s climate?
T
10. Precession of Earth's axis causes the date at which perihelion of Earth's orbit occurs to slowly
change.
FILL-IN-THE BLANK
GUIDEPOST CATEGORY: How can you compare the brightness of the stars?
1.
Star A has an apparent visual magnitude of 6.3 and star B has an apparent visual magnitude of 5.3. Star
A is _________ times ________ than star B.
** 2.5
fainter
GUIDEPOST CATEGORY: How does the sky move as the Earth moves?
2.
The ________ is the point on the celestial sphere directly above an observer, regardless of where the
observer is located on Earth.
** Zenith
GUIDEPOST CATEGORY: What causes the seasons?
3.
__________ is a measure of the light energy that hits one square meter in one second.
** Intensity
GUIDEPOST CATEGORY: How do astronomical cycles affect Earth’s climate?
4.
_________ is the point in Earth's orbit when Earth is closest to the sun.
** Perihelion
BRIEF ESSAY
GUIDEPOST CATEGORY: How can you compare the brightness of the stars?
1.
What information does a star's Greek letter designation convey?
GUIDEPOST CATEGORY: How does the sky move as the Earth moves?
2.
Which planets are never visible near the eastern horizon at sunset?
** Mercury and Venus
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Chapter 2
Seeds’ FOUNDATIONS OF ASTRONOMY Instructors Manual and Test Bank 9e
Revised by Gene Byrd
3.
4.
Describe the path that a star on the celestial equator follows from the time it rises until it sets for
a.
a person at a latitude of 60° N.
b.
a person at the equator.
Describe the location of Polaris in the sky relative to the horizon as seen by observers in Alaska (lat. =
60° N), Texas (lat. = 33° N), Ecuador (lat. = 0°), and Australia (lat. = 30° S).
5.
How are the celestial poles and equator defined by Earth's rotation?
6.
Why isn't the winter solstice the coldest day of the year?
7.
Give two reasons why summer days are warmer than winter days.
8.
Why can neither Venus nor Mercury remain visible throughout the night as the full moon does?
9.
What causes precession and why does it move the celestial equator?
GUIDEPOST CATEGORY: How do astronomical cycles affect Earth’s climate?
10. Describe how a small change in the relative distance of Earth from the sun at perihelion could effect the
formation of glaciers on Earth.
11. Describe the evidence that best supports the Milankovitch hypothesis.
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Chapter 2