Transcript Universe 8/e Chapter 2 - Physics and Astronomy

Roger A. Freedman • William J. Kaufmann III
Universe
Eighth Edition
CHAPTER 2
Knowing the Heavens
Homework 2
Read Chapter 3 (Eclipses and the Motion of the
Moon)
Online quiz from Chapter 2
DUE Friday 9/10 @ 5 pm
REMINDER: No class on Monday 9/6 (Labor Day)
By reading this chapter, you will learn
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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
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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 Earth’s
axis of rotation
2-7 The role of astronomy
in measuring time
2-8 How the modern
calendar developed
Most evidence suggests ancient astronomers were
inspired to look at the sky because
A.
B.
C.
D.
E.
Q2.2
they wanted to create scientific theories of the
world in which they lived.
observation of star positions allowed calendars
to be created.
ancient civilizations associated star patterns with
gods and mystical figures.
Both a and c.
Both b and c.
Most evidence suggests ancient astronomers were
inspired to look at the sky because
A.
B.
C.
D.
E.
A2.2
they wanted to create scientific theories of the
world in which they lived.
observation of star positions allowed calendars
to be created.
ancient civilizations associated star patterns with
gods and mystical figures.
Both a and c.
Both b and c.
In the southern hemisphere
A.
B.
C.
D.
E.
Q2.4
stars rise in the east and set in the west.
stars rise in the west and set in the east.
all stars are circumpolar.
no stars are circumpolar.
a or b, depending on the time of day.
In the southern hemisphere
A.
B.
C.
D.
E.
A2.4
stars rise in the east and set in the west.
stars rise in the west and set in the east.
all stars are circumpolar.
no stars are circumpolar.
a or b, depending on the time of day.
Summer occurs in the northern hemisphere of the
Earth in June, July, and August because
A.
B.
C.
D.
E.
Q2.5
the northern hemisphere of Earth is closer to the
Sun than the southern hemisphere.
days are longer in the northern hemisphere than
in the southern hemisphere.
the sunlight strikes the northern hemisphere of
the Earth at an angle closer to the vertical.
the Earth is closer to the Sun.
Both b and c.
Summer occurs in the northern hemisphere of the
Earth in June, July, and August because
A.
B.
C.
D.
E.
A2.5
the northern hemisphere of Earth is closer to the
Sun than the southern hemisphere.
days are longer in the northern hemisphere than
in the southern hemisphere.
the sunlight strikes the northern hemisphere of
the Earth at an angle closer to the vertical.
the Earth is closer to the Sun.
Both b and c.
If the Earth’s axis were not tilted,
A.
B.
C.
D.
E.
Q2.6
a day and night would last 365 Earth days.
the effect of seasons would be exaggerated.
there would be no seasons.
the Earth would always keep the same side
facing toward the Sun.
The Earth would be completely covered with ice.
If the Earth’s axis were not tilted,
A.
B.
C.
D.
E.
A2.6
a day and night would last 365 Earth days.
the effect of seasons would be exaggerated.
there would be no seasons.
the Earth would always keep the same side
facing toward the Sun.
The Earth would be completely covered with ice.
The point on the ecliptic (see diagram) where the
Sun crosses from the southern to the northern
hemisphere is the
A.
B.
C.
D.
E.
Q2.10
summer solstice.
winter solstice.
autumnal equinox.
vernal equinox.
celestial equator.
The point on the ecliptic (see diagram) where the
Sun crosses from the southern to the northern
hemisphere is the
A.
B.
C.
D.
E.
A2.10
summer solstice.
winter solstice.
autumnal equinox.
vernal equinox.
celestial equator.
Key Ideas
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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).
Key Ideas
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Seasons and the Tilt of the Earth’s Axis: The Earth’s
axis of rotation is tilted at an angle of about 231⁄2° from
the perpendicular to the plane of the Earth’s orbit.
The seasons are caused by the tilt of the Earth’s 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.
Key Ideas
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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.
Key Ideas
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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.