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Chapter Introduction
Lesson 1 The View from Earth
Lesson 2 The Sun and
Other Stars
Lesson 3 Evolution
of Stars
Lesson 4 Galaxies and
the Universe
Chapter Wrap-Up
What makes up the
universe and how
does gravity affect
the universe?
Do you agree or disagree?
1. The night sky is divided into
constellations.
2. A light-year is a measurement of time.
3. Stars shine because there are nuclear
reactions in their cores.
4. Sunspots appear dark because they
are cooler than nearby areas.
Do you agree or disagree?
5. The more matter a star contains, the
longer it is able to shine.
6. Gravity plays an important role in the
formation of stars.
7. Most of the mass in the universe is in
stars.
8. The Big Bang theory is an explanation
of the beginning of the universe.
The View from Earth
• How do astronomers divide the night
sky?
• What can astronomers learn about
stars from their light?
• How do scientists measure the
distance and the brightness of objects
in the sky?
Looking at the Night Sky
• The star Polaris is
almost directly
above the North
Pole.
• Earth’s rotation
causes other stars
to appear to
revolve around
Polaris.
CORBIS
Present-day astronomers use many
ancient constellations to divide the sky into
88 regions.
Dividing the sky helps scientists
communicate to others what area of sky
they are studying.
Looking at the Night Sky (cont.)
How do astronomers divide the
night sky?
Looking at the Night Sky (cont.)
Telescopes can
collect more light than
the human eye can.
Steve Allen/Brand X Pictures
Michael Matisse/Getty Images
Looking at the Night Sky (cont.)
The electromagnetic spectrum is a
continuous range of wavelengths.
Different parts of the electromagnetic
spectrum have different wavelengths and
different energies. You can see only a small
part of the energy in these wavelengths.
Looking at the Night Sky (cont.)
• The set of wavelengths that a star
emits is the star’s spectrum.
• A spectroscope spreads light into
different wavelengths.
• Using spectroscopes, astronomers can
study stars’ characteristics, including
temperatures, compositions, and
energies.
Looking at the Night Sky (cont.)
What can astronomers learn from
a star’s spectrum?
Measuring Distances
Parallax is the apparent change in an
object’s position caused by looking at it
from two different points.
parallax
from Greek parallaxis, means
“alteration”
• Astronomers use parallax to calculate
how far an object in space is from Earth.
• The object is viewed from two extreme
points in Earth’s orbit.
An astronomical unit is the average
distance between Earth and the Sun,
about 150 million km.
Measuring Distances (cont.)
• A light-year is the distance light travels
in 1 year.
• One light-year is about 10 trillion km.
Measuring Brightness
The apparent magnitude of an object is
a measure of how bright it appears from
Earth.
Measuring Brightness (cont.)
• Luminosity is the true brightness of an
object.
• The luminosity of a star, measured on an
absolute magnitude scale, depends on
the star’s temperature and size, not its
distance from Earth.
Measuring Brightness (cont.)
How do scientists measure
the brightness of stars?
• Astronomers
use ancient
constellations
to divide the sky
into sections,
also called
constellations.
• Different wavelengths of the
electromagnetic spectrum carry
different energies.
• Astronomers
measure
distances
within the solar
system using
astronomical
units.
Which term refers to how bright
an object appears from Earth?
A. luminosity
B. light-year
C. apparent magnitude
D. absolute magnitude
One light-year is equal to about
how many kilometers?
A. one million
B. ten million
C. one trillion
D. ten trillion
Which term refers to the range
of wavelengths a star emits?
A. brightness
B. luminosity
C. magnitude
D. spectrum
Do you agree or disagree?
1. The night sky is divided into
constellations.
2. A light-year is a measurement of time.
The Sun and Other Stars
• How do stars shine?
• How are stars layered?
• How does the Sun change over short
periods of time?
• How do scientists classify stars?
How Stars Shine
• A star is a large ball of gas held together
by gravity with a core so hot that nuclear
fusion occurs.
• Nuclear fusion occurs when the nuclei
of several atoms combine into one larger
nucleus.
How Stars Shine (cont.)
• Nuclear fusion releases a large amount
of energy.
• A star shines because when energy
leaves a star’s core, it travels throughout
the star and radiates into space.
How Stars Shine (cont.)
How do stars shine?
Composition and Structure of Stars
Spectra of the Sun and other stars provide
information about stellar composition.
stellar
Science Use anything related
to stars
Common Use outstanding,
exemplary
Composition and Structure of Stars
(cont.)
• There are three
interior layers of
a typical star.
• When first formed,
all stars fuse
hydrogen into
helium in their
cores.
Composition and Structure of Stars
(cont.)
• The radiative zone
is a shell of cooler
hydrogen around a
star’s core.
• In the convection
zone, hot gases
move toward the
surface as cooler
gases move down
into the interior.
Composition and Structure of Stars
(cont.)
What are the interior layers
of a star?
Composition and Structure of Stars
(cont.)
Beyond the convection zone are
the three layers of a star’s atmosphere—
the photosphere, the chromosphere, and
the corona.
Composition and Structure of Stars
(cont.)
The photosphere is
the apparent surface
of a star, where light
energy radiates into
space.
Composition and Structure of Stars
(cont.)
• The chromosphere
is the orange-red
layer above the
photosphere.
• The corona is the
wide, outermost
layer of a star’s
atmosphere.
Changing Features of the Sun:
Sunspots
• Cooler regions of
magnetic activity
• Seem to move as
the Sun rotates
• Number varies on
an 11-year cycle
Digital Vision/PunchStock
Changing Features of the Sun:
Coronal Mass Ejections (CMEs)
• Huge gas bubbles
ejected from the
corona
• Larger than flares
• May reach Earth
• Can cause radio
blackouts
NASA
Changing Features of the Sun:
Prominences and Flares
• Prominences—
clouds and jets of
gases forming loops
into the corona
• Flares—sudden
increases in
brightness, often
near sunspots or
prominences
SOHO Consortium, ESA, NASA
Changing Features of the Sun:
The Solar Wind
• Caused by
charged particles
streaming away
from the Sun
• Extends to the
edge of the solar
system
• Causes auroras
CORBIS
Groups of Stars
• Most stars exist in star systems bound
by gravity.
• Many stars exist in large groupings
called clusters.
• Stars in a cluster all formed at about the
same time and are the same distance
from Earth.
Classifying Stars
• Scientists classify stars according to
their spectra.
• Though there are exceptions, color in
most stars is related to mass.
Blue-white stars tend to have the most
mass, followed by white stars, yellow stars,
orange stars, and red stars.
The Hertzsprung-Russell diagram
is a graph that plots luminosity against
temperature of stars.
The y-axis of the H-R diagram displays
increasing luminosity and the x-axis
displays decreasing temperature.
Most stars exist along the main sequence.
The mass of a main-sequence star
determines both its temperature and its
luminosity
Classifying Stars (cont.)
What is the HertzsprungRussell diagram?
• Hot gas moves up
and cool gas moves
down in the Sun’s
convection zone.
• Sunspots are relatively dark areas on
the Sun that have strong magnetic
activity.
• Globular clusters contain hundreds
of thousands of stars.
Which term refers to the wide,
outermost layer of a star’s
atmosphere?
A. radiative zone
B. corona
C. convection zone
D. chromosphere
Scientists classify stars
according to which of these?
A. mass
B. size
C. spectra
D. temperature
What color of stars tend to have
the most mass?
A. yellow
B. red
C. orange
D. blue-white
Do you agree or disagree?
3. Stars shine because there are nuclear
reactions in their cores.
4. Sunspots appear dark because they
are cooler than nearby areas.
Evolution of Stars
• How do stars form?
• How does a star’s mass affect its
evolution?
• How is star matter recycled in space?
Life Cycle of a Star
• Stars form deep inside clouds of gas
and dust.
• A cloud of gas and dust is a nebula.
nebula
from Latin nebula, means
“mist” or “little cloud”