Download Stars and Galaxies - La Salle Elementary Public Schools No 122

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?
What do you think?
Before you begin, decide if you agree or
disagree with each of these statements.
As you view this presentation, see if you
change your mind about any of the
statements.
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?
The View from Earth
• spectroscope
• astronomical unit
• light-year
• apparent magnitude
• luminosity
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?
The Sun and Other Stars
• nuclear fusion
• photosphere
• star
• chromosphere
• radiative zone
• corona
• convection
zone
• HertzsprungRussell
diagram
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?
Evolution of Stars
• nebula
• white dwarf
• supernova
• neutron star
• black hole
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”
Life Cycle of a Star (cont.)
Star-forming nebulae are cold, dense,
and dark.
Photo courtesy of NASA/Corbis
Life Cycle of a Star (cont.)
• Gravity causes the densest parts to
collapse, forming regions called
protostars.
• Over many thousands of years, the
energy produced by protostars heats
the gas and dust surrounding them.
Life Cycle of a Star (cont.)
How do stars form?
Life Cycle of a Star (cont.)
• A star becomes a main-sequence star
as soon as it begins to fuse hydrogen
into helium.
• Low-mass stars stay on the main
sequence for billions of years, and
high-mass stars are there for only a few
million years.
Life Cycle of a Star (cont.)
• When a star’s hydrogen supply is
nearly gone, the star leaves the main
sequence and begins the next stage
of its life cycle.
• All stars form in the same way, but
stars die in different ways, depending
on their masses.
• Massive stars eventually become red
supergiants.
End of a Star
• After helium in the cores of lower-mass
stars is gone, the stars cast off their
gases exposing their cores.
• The core eventually becomes a white
dwarf, a hot, dense, slowly cooling
sphere of carbon.
• This is what is expected to happen to the
Sun.
The Sun will remain on the main
sequence for 5 billion more years.
When the Sun becomes a red giant for the
second time, it will probably absorb Earth and
push Mars and Jupiter outward.
When the Sun becomes a white dwarf, the
solar system will be a cold, dark place.
End of a Star (cont.)
• Very massive stars can explode in a
supernova, which destroys the star.
• Iron in the core does not fuse and the
core collapses quickly under the force of
gravity.
• The normal space within atoms is
eliminated, leaving a dense core of
neutrons, or a neutron star.
End of a Star (cont.)
• For the most massive stars, atomic
forces holding neutrons together are not
strong enough to overcome so much
mass in such a small volume. Gravity is
too strong, and the matter crushes into a
black hole.
• A black hole is an object whose gravity
is so great that no light can escape.
End of a Star (cont.)
How does a star’s mass determine
if it will become a white dwarf, a
neutron star, or a black hole?
Recycling Matter
• When a star becomes a white dwarf, it
casts off hydrogen and helium gases in
its outer layers.
• The expanding, cast-off matter of a white
dwarf is a planetary nebula.
• During a supernova, a massive star
comes apart sending a shock wave into
space.
Recycling Matter (cont.)
• The expanding cloud of dust and gas is
called a supernova remnant.
• Gravity causes recycled gases and other
matter to clump together in nebulae and
form new stars and planets.
Recycling Matter (cont.)
How do stars recycle
matter?
• Iron is formed in
the cores of the
most massive
stars.
• The Sun will
become a red
giant in about
5 billion years.
• Matter is
recycled in
supernovae.
What term refers to clouds of gas
and dust where stars form?
A. white dwarf
B. supernova
C. nebula
D. black hole
What type of star is a hot, dense,
slowly cooling sphere of carbon?
A. neutron star
B. red giant
C. supernova
D. white dwarf
Which of these is an object
whose gravity is so great that
no light can escape?
A. white dwarf
B. supernova
C. nebula
D. black hole
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.
Galaxies and the Universe
• What are the major types of galaxies?
• What is the Milky Way, and how is it
related to the solar system?
• What is the Big Bang theory?
Galaxies and the Universe
• galaxy
• dark matter
• Big Bang theory
• Doppler shift
Galaxies
Galaxies are huge collections of stars.
galaxy
from Greek galactos, means “milk”
Galaxies (cont.)
• Gravity holds stars and galaxies
together.
• When astronomers examine how
galaxies rotate and gravitationally
interact, they find that most of the matter
in galaxies is invisible.
• Matter that emits no light at any
wavelength is dark matter.
Types of Galaxies: Spiral Galaxies
• Spiral arms of
stars, gas, and
dust extend
from central disk.
• Spiral galaxies
have a central
bulge.
• A spherical halo
surrounds the disk.
NASA/JPL-Caltech/S. Willner (Harvard-Smithsonian Center for Astrophysics)
Types of Galaxies: Elliptical Galaxies
• Elliptical galaxies
have a spherical or
elliptical shape and
no internal structure.
• They contain more
older stars than
spiral galaxies, and
may have formed as
spiral galaxies merged.
JPL/NASA
Types of Galaxies: Irregular Galaxies
Irregular
galaxies are
oddly shaped
and contain
many young
stars.
Local Group Galaxies Survey Team, NOAO, AURA, NSF
Galaxies (cont.)
What are the major
types of galaxies?
The Milky Way
• The solar system is in the Milky Way, a
spiral galaxy that contains gas, dust, and
almost 200 billion stars.
• The Milky Way is a member of the Local
Group, a cluster of about 30 galaxies.
The Milky Way (cont.)
Where is Earth in the Milky Way?
The Big Bang Theory
According to the Big Bang theory, the
universe began from one point billions of
years ago and has been expanding ever
since.
What is the Big Bang theory?
The Big Bang Theory (cont.)
• Most scientists agree that the universe is
13-14 billion years old.
• Scientists observe how space stretches
by measuring the speed at which
galaxies move away from the Earth.
The Big Bang Theory (cont.)
• When light travels away from you, its
wavelength stretches out, shifting to the
red end of the electromagnetic spectrum.
• The shift to a different wavelength is
called the Doppler shift.
Doppler Shift
• By studying interacting galaxies,
scientists have determined that most
mass in the universe is dark matter.
• The Sun is one of billions of stars in
the Milky Way.
• When an object
moves away, its
light stretches
out, just as a
siren’s sound
waves stretch
out as the siren
moves away.
What term refers to matter that
emits no light at any wavelength?
A. clusters
B. dark matter
C. H-R matter
D. light matter
The Milky Way is a member of the
Local Group which is a cluster of
about how many galaxies?
A. 5
B. 30
C. 200
D. 1 billion
Approximately what is the age of
the universe?
A. 1-2 million years
B. 9-10 million years
C. 4-5 billion years
D. 13-14 billion years
Do you agree or disagree?
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.
Key Concept Summary
Interactive Concept Map
Chapter Review
Standardized Test Practice
The universe is made
up of stars, gas, and
dust, as well as
invisible dark matter.
Material in the universe
is not randomly
arranged, but is pulled
by gravity into galaxies.
Lesson 1: The View from Earth
• The sky is divided into 88 constellations.
• Astronomers learn about the energy, distance,
temperature, and composition of stars by studying
their light.
• Astronomers measure distances in space in
astrological units and in light-years. They measure
star brightness as apparent magnitude and as
luminosity.
Lesson 2: The Sun and Other Stars
• Stars shine because of nuclear fusion in their cores.
• Stars have a layered structure—they conduct
energy through their radiative zones and their
convection zones and release the energy at their
photospheres.
• Sunspots, prominences, flares, and coronal mass
ejections are temporary phenomena on the Sun.
• Astronomers classify
stars by their
temperatures
and luminosities.
Lesson 3: Evolution of Stars
• Stars are born in clouds of gas and dust called
nebulae.
• What happens to a star when it leaves the main
sequence depends on its mass.
• Matter is recycled in the
planetary nebulae of white
dwarfs and the remnants
of supernovae.
Lesson 4: Galaxies and the Universe
• The three major types of galaxies are spiral,
elliptical, and irregular.
• The Milky Way is the spiral galaxy
that contains the solar system.
• The Big Bang theory explains the
origin of the universe.
Which of these describes the
average distance between Earth
and the Sun?
A. astronomical unit
B. Doppler shift
C. light-year
D. solar distance
The true brightness of an object
can also be referred to as which
of these?
A. apparent magnitude
B. astronomical unit
C. luminosity
D. spectrum
Which term refers to the apparent
surface of a star?
A. chromosphere
B. convection zone
C. corona
D. photosphere
Which is an enormous explosion
that destroys a star?
A. supernova
B. nebula
C. Hertzsprung-Russell event
D. Doppler shift
The universe began from one
point billions of years ago and
has been expanding ever since,
according to which of these?
A. Big Bang theory
B. Doppler shift
C. H-R diagram
D. law of magnitude
Which of these refers to the
distance light travels in one year?
A. astronomical unit
B. light-year
C. solar magnitude
D. 2 trillion km
Which of these spreads light into
different wavelengths?
A. telescope
B. spectroscope
C. photosphere
D. dark matter
Which of these is the shell of
cooler hydrogen above a star’s
core?
A. radiative zone
B. photosphere
C. corona
D. convection zone
Which of these is the dense core
of matter left from a supernova?
A. white dwarf
B. neutron star
C. nebula
D. black hole
Which term refers to huge
collections of stars?
A. galaxies
B. dark matter
C. clusters
D. astronomical units