Universe 8/e Chapter 2

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Roger A. Freedman William J. Kaufmann III
Universe Eighth Edition
CHAPTER 2 Knowing the Heavens
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Homework 2 Read Chapter 3 (Eclipses and the
Motion of the Moon) Online quiz from Chapter
2 DUE Friday 9/10 _at_ 5 pm REMINDER No class on
Monday 9/6 (Labor Day)
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By reading this chapter, you will learn

• 2-1 The importance of astronomy in ancient
  civilizations around the world
• 2-2 That regions of the sky are divided around
  groups of stars called constellations
• 2-3 How the sky changes from night to night

• 2-4 How astronomers locate objects in the sky
• 2-5 What causes the seasons
• 2-6 The effect of changes in the direction of
  Earths axis of rotation
• 2-7 The role of astronomy in measuring time
• 2-8 How the modern calendar developed

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Most evidence suggests ancient astronomers were
inspired to look at the sky because

1. they wanted to create scientific theories of the
   world in which they lived.
2. observation of star positions allowed calendars
   to be created.
3. ancient civilizations associated star patterns
   with gods and mystical figures.
4. Both a and c.
5. Both b and c.

Q2.2
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Most evidence suggests ancient astronomers were
inspired to look at the sky because

1. they wanted to create scientific theories of the
   world in which they lived.
2. observation of star positions allowed calendars
   to be created.
3. ancient civilizations associated star patterns
   with gods and mystical figures.
4. Both a and c.
5. Both b and c.

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In the southern hemisphere

1. stars rise in the east and set in the west.
2. stars rise in the west and set in the east.
3. all stars are circumpolar.
4. no stars are circumpolar.
5. a or b, depending on the time of day.

Q2.4
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In the southern hemisphere

1. stars rise in the east and set in the west.
2. stars rise in the west and set in the east.
3. all stars are circumpolar.
4. no stars are circumpolar.
5. a or b, depending on the time of day.

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Summer occurs in the northern hemisphere of the
Earth in June, July, and August because

1. the northern hemisphere of Earth is closer to the
   Sun than the southern hemisphere.
2. days are longer in the northern hemisphere than
   in the southern hemisphere.
3. the sunlight strikes the northern hemisphere of
   the Earth at an angle closer to the vertical.
4. the Earth is closer to the Sun.
5. Both b and c.

Q2.5
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Summer occurs in the northern hemisphere of the
Earth in June, July, and August because

1. the northern hemisphere of Earth is closer to the
   Sun than the southern hemisphere.
2. days are longer in the northern hemisphere than
   in the southern hemisphere.
3. the sunlight strikes the northern hemisphere of
   the Earth at an angle closer to the vertical.
4. the Earth is closer to the Sun.
5. Both b and c.

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If the Earths axis were not tilted,

1. a day and night would last 365 Earth days.
2. the effect of seasons would be exaggerated.
3. there would be no seasons.
4. the Earth would always keep the same side facing
   toward the Sun.
5. The Earth would be completely covered with ice.

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If the Earths axis were not tilted,

1. a day and night would last 365 Earth days.
2. the effect of seasons would be exaggerated.
3. there would be no seasons.
4. the Earth would always keep the same side facing
   toward the Sun.
5. The Earth would be completely covered with ice.

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The point on the ecliptic (see diagram) where the
Sun crosses from the southern to the northern
hemisphere is the

1. summer solstice.
2. winter solstice.
3. autumnal equinox.
4. vernal equinox.
5. celestial equator.

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The point on the ecliptic (see diagram) where the
Sun crosses from the southern to the northern
hemisphere is the

1. summer solstice.
2. winter solstice.
3. autumnal equinox.
4. vernal equinox.
5. celestial equator.

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Key Ideas

• Constellations and the Celestial Sphere It is
  convenient to imagine the stars fixed to the
  celestial sphere with the Earth at its center.
• The surface of the celestial sphere is divided
  into 88 regions called constellations.
• Diurnal (Daily) Motion of the Celestial Sphere
  The celestial sphere appears to rotate around the
  Earth once in each 24-hour period. In fact, it is
  actually the Earth that is rotating.
• The poles and equator of the celestial sphere are
  determined by extending the axis of rotation and
  the equatorial plane of the Earth out to the
  celestial sphere.
• The positions of objects on the celestial sphere
  are described by specifying their right ascension
  (in time units) and declination (in angular
  measure).

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Key Ideas

• Seasons and the Tilt of the Earths Axis The
  Earths axis of rotation is tilted at an angle of
  about 231/2 from the perpendicular to the plane
  of the Earths orbit.
• The seasons are caused by the tilt of the Earths
  axis.
• Over the course of a year, the Sun appears to
  move around the celestial sphere along a path
  called the ecliptic. The ecliptic is inclined to
  the celestial equator by about 231/2.
• The ecliptic crosses the celestial equator at two
  points in the sky, the vernal and autumnal
  equinoxes.
• The northernmost point that the Sun reaches on
  the celestial sphere is the summer solstice, and
  the southernmost point is the winter solstice.

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Key Ideas

• Because the system of right ascension and
  declination is tied to the position of the vernal
  equinox, the date (or epoch) of observation must
  be specified when giving the position of an
  object in the sky.

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Key Ideas

• Timekeeping Astronomers use several different
  means of keeping time.
• Apparent solar time is based on the apparent
  motion of the Sun across the celestial sphere,
  which varies over the course of the year.
• Mean solar time is based on the motion of an
  imaginary mean sun along the celestial equator,
  which produces a uniform mean solar day of 24
  hours. Ordinary watches and clocks measure mean
  solar time.
• Sidereal time is based on the apparent motion of
  the celestial sphere.
• The Calendar The tropical year is the period
  between two passages of the Sun across the vernal
  equinox. Leap year corrections are needed because
  the tropical year is not exactly 365 days. The
  sidereal year is the actual orbital period of the
  Earth.