Transcript CA_Sci8_Chapter_12

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Lesson 1: Stars
Lesson 2: How Stars Shine
Lesson 3: Galaxies
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12.1 Stars
light-year
luminosity
apparent magnitude
absolute magnitude
12.1 Stars
What are stars?
• Stars are balls of gas, mostly hydrogen,
that produce light by nuclear fusion
reactions in their cores.
12.1 Stars
The Structure of Stars
• Stars have layered structures.
• Energy is produced in the core.
• Temperatures range from
5,000,000K to
100,000,000K in the core.
• Here Hydrogen nuclei fuse to
Helium, giving off heat and light
energy, according to Einstein’s
E=mc squared equation
12.1 Stars
Types of Stars
• Stars have many sizes, masses, and
surface temperatures.
• Our Sun is a medium-sized star with a
surface temperature of about 5800K.
12.1 Stars
Distances Between Stars
• One AU is the average distance between
the Sun and Earth.
• A light-year is the distance light travels
in one year—9,500,000,000,000 km or
63,000 AU. Remember: Distance =
Speed x time
12.1 Stars
What are stars made of?
• Stars can only be studied by the
light they emit. Remember, we’ve
never gone to another star system
• A spectroscope is an instrument
that is used to study light.
• Astronomers use spectroscopes
to determine what elements are
present in stars
How does the chemical
composition of stars
determine their
classification?
12.1 Stars
Continuous Spectra
• Light split by a prism into a rainbow is a
continuous spectrum.
• A continuous spectrum is emitted by hot,
dense materials, such as the gas of the
Sun’s photosphere.
• Each star’s temperature and composition
give it its own “fingerprint” or spectrum.
12.1 Stars
Absorption Spectra
• Dark lines are sometimes seen in a
spectrum, called an absorption spectra.
• Absorption spectra are produced when a
star’s light passes through cooler gases
(between us and the star) that absorb
certain wavelengths, depending on its
makeup.
• When a stars light passes through clouds
of gas and dust, the absorption spectrum
tells us what the gas and dust are made of.
12.1 Stars
Absorption Spectra (cont.)
• Each element absorbs only certain
wavelengths.
12.1 Stars
Identifying Elements in a Star
• Absorption lines help astronomers identify
elements in stars.
12.1 Stars
Temperature and Color of Stars
• As metal gets hotter, it changes from red
to yellow to white.
• The color of stars, in the same way, also
depends on temperature.
12.1 Stars
Temperature and Wavelengths Emitted
• Every object emits electromagnetic radiation.
• The wavelength emitted depends on the
temperature of the object.
– Objects at room temperature emit long,
infrared waves.
– As temperature rises, wavelengths
become shorter.
12.1 Stars
Temperature and Wavelengths Emitted
(cont.)
12.1 Stars
The Brightness of Stars
• The brightness of stars depends on two
things—energy and distance.
• Light looks brighter as you move closer to
the source.
12.1 Stars
Luminosity
• Luminosity is measured by how much
energy in joules is released per second.
• One joule per second is called a watt (like
in light bulbs)
• So, a 60 watt bulb gives off 60 joules of
energy in the form of light and heat every
second
12.1 Stars
Apparent Magnitude
• Apparent magnitude is the apparent
brightness of a star as measured on Earth.
– Apparent magnitude depends on the
star’s actual brightness and distance.
– The smaller the magnitude number,
the brighter the star. The bigger the
number, the dimmer the star seems to
us on earth.
12.1 Stars
Absolute Magnitude
• Absolute magnitude is the apparent
magnitude it would have if it were 32.6 light
years away from Earth.
12.1 Stars
Classifying Stars—The H-R Diagram
• Two astronomers independently
developed similar diagrams of how
absolute magnitude, or luminosity, is
related to the temperature of stars.
• These two were Hertzbsprung and
Russell, and the diagram is known as the
Hertzsprung-Russell diagram chart of star
magnitude, or H-R diagram for short.
• It relates brightness, size and luminosity
12.1 Stars
Classifying Stars—The H-R Diagram
• 90% of stars fall on a diagonal, curved
line, called the main sequence.
• The remaining stars fall into one of three
other groups.
– Red giants
– Supergiants
– White dwarfs
(cont.)
12.1 Stars
12.1 Stars
12.1 Stars
How much brighter is a star with
a magnitude of 2.0 than a star
with a magnitude of 4.0?
A 5 times
B 10 times
C 2.5 times
D 2 times
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12.1 Stars
The apparent brightness of a star
depends on what two things?
A magnitude and
distance
B distance and
temperature
C distance and
absolute brightness
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D absolute brightness
and temperature
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12.1 Stars
A light-year is a unit of ____.
A time
B temperature
C brightness
D distance
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12.2 How Stars Shine
nebula
nuclear fusion
red giant
white dwarf
supernova
neutron star
black hole
12.2 How Stars Shine
How Stars Form
• The universe consists mostly of light
elements such as hydrogen and helium.
• Stars form in a nebula, which is a large
cloud of gas and dust in space.
How Stars Form (cont.)
12.2 How Stars Shine
Matter in a Nebula
• Interstellar space is the space between
stars containing mostly gas and dust at
very low (it’s a vacuum!!) densities.
• In a nebula, the density of gas and dust is
much greater and can form clouds.
• The dust is mostly carbon clumps (similar
to soot) and silicon molecules (much like
sand and rock dust).
12.2 How Stars Shine
Contraction and Heating
• If the nebula is dense enough,
Gravitational forces in a nebula cause
matter to form clumps.
• As gravity pulls the nebula in on itself, it
gets denser and hotter, the way air in a
bike tire gets hotter when you pump it up.
12.2 How Stars Shine
Protostars
• As the clump contracts, it becomes
spherical and rotates
• When it reaches a certain mass, it
becomes a protostar.
• The protostar continues to contract and
increase in temperature.
12.2 How Stars Shine
Protostars (cont.)
• The sphere begins to rotate and flatten
into a disk.
• After millions of years, gravity makes the
temperature and density in the central
mass is hot enough for fusion to occur.
• When the central mass reaches 8% that of
the Sun, a star is born.
12.2 How Stars Shine
How Stars Produce Light
• Stars emit huge amounts of energy, part of
which is visible light.
• Energy produced during fusion passes
through the star and is emitted from its
photosphere.
12.2 How Stars Shine
Nuclear Fusion
• In a nuclear fusion reaction, two nuclei
combine to form a larger nuclei.
• In a star’s core, there is a reaction that
fuses hydrogen to helium
• Energy is released as gamma rays and
neutrinos.
• By the time the energy reaches the star’s
photosphere, its primarily in the form of
light and heat
12.2 How Stars Shine
Nuclear Fusion (cont.)
12.2 How Stars Shine
The Balance Between Pressure
and Gravity
• Heat from fusion reactions produces
outward pressure and causes expansion
• Gravity pulls particles toward each other
and causes contraction.
• The life of a star is determined by the
balance of these forces: hot gas expanding
versus gravity pulling inward
12.2 How Stars Shine
The Balance Between Pressure
and Gravity (cont.)
12.2 How Stars Shine
How Stars Come to an End
• Eventually a star converts all its hydrogen
to helium.
• In smaller stars, fusion will continue to
convert helium into carbon, nitrogen, and
oxygen.
• In very massive stars, fusion reactions
continue to produce heavier elements.
• When fusion stops, there is no longer any
force to balance gravity.
12.2 How Stars Shine
How Stars Come to an End
(cont.)
• When fusion stops, there is no longer any
force to balance gravity.
• The result could be a white dwarf, a
supernova, a neutron star, or a black hole.
• The size/mass of the star determines how
the star will end its life
• The sun is medium size, and will end as a
white dwarf.
How Stars Come to an End
(cont.)
12.2 How Stars Shine
The Life Cycle of Low-Mass Stars
• Red giants are sun-sized stars that have
used up all the fuel in their core and have
begun to expand their outer layers
• White dwarfs are red giants that have lost
the mass from their surface and only the
core remains.
12.2 How Stars Shine
The Life Cycle of Low-Mass Stars (cont.)
12.2 How Stars Shine
The Life Cycle of High-Mass Stars
• A supernova forms when a supergiant
explodes before dying.
12.2 How Stars Shine
Neutron Stars
• Neutron stars are the remains of stars
after a supernova.
• Neutron stars are very dense.
12.2 How Stars Shine
Black Holes
• Black holes are created when a neutron
star collapses and all its mass is
concentrated into a single point.
12.2 How Stars Shine
Black Holes (cont.)
• The gravitation force in a black hole is so
great not even light can escape.
• Black holes can be detected by their
influence on other nearby objects.
12.2 How Stars Shine
Interstellar space is composed of
mainly ____.
A nothing
B iron
C hydrogen
D dust
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12.2 How Stars Shine
Which type of star has a density so
great that protons fuse to electrons?
A red giant
B supernova
C neutron star
D white dwarf
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12.2 How Stars Shine
In nuclear fusion, smaller nuclei
fused to form ____.
A hydrogen
B helium
C lighter elements
D larger nuclei
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12.3 Galaxies
galaxy
Big Bang theory
12.3 Galaxies
Stars Cluster in Galaxies
• Stars are not uniformly distributed through
the universe but gather in large groups
called galaxies.
• Galaxies contain
billions of stars.
• Star clusters
within galaxies
contain millions
of stars.
12.3 Galaxies
Types of Galaxies
• Galaxies have different sizes and shapes.
• Spiral galaxies can be regular or barred.
12.3 Galaxies
Types of Galaxies (cont.)
• Both types have spiral arms when viewed
from above.
• They have three components—the
nucleus, arms, and halos.
12.3 Galaxies
Types of Galaxies (cont.)
• The spiral arms are star-forming regions
and the halo contains mostly old star
clusters.
• From the side, spiral galaxies look flat.
12.3 Galaxies
Types of Galaxies (cont.)
• Some galaxies contain a bar of stars, dust,
and gas that passes through the center of
the galaxy—these are called barred spirals.
12.3 Galaxies
The Milky Way
• Our solar system is located in the
Milky Way galaxy.
12.3 Galaxies
Elliptical and Irregular Galaxies
• Elliptical galaxies have an oval shape and
are composed of old, reddish stars.
• Irregular galaxies have a patchy
appearance and are difficult to classify.
• Computer models and observation now
show Elliptical galaxies are the result of the
collision and merger of several galaxies
• Irregular galaxies are messed up as a
result of collisions or near collisions with
other galaxies
12.3 Galaxies
The Distances Between Galaxies
• Galaxies are so
far away that
even the closest
galaxies appear
as fuzzy patches
of light.
12.3 Galaxies
The Local Group
• Galaxies are grouped together into
clusters, which form superclusters.
• The Milky Way is part of a cluster called
the Local Group.
12.3 Galaxies
Superclusters
• Our cluster is part of the Virgo supercluster.
• The Virgo supercluster contains thousands
of galaxies spread across 100 million light
years.
• The farthest galaxies from Earth are about
13 billion light years away.
12.3 Galaxies
The Big Bang Theory
• In the late 1920s, Edwin Hubble discovered
that most of the galaxies he observed were
moving away from Earth.
• This could only be explained if the entire
universe as expanding.
• The Big Bang Theory states the
expansion of the universe began about
14 billion years ago.
12.3 Galaxies
The Big Bang Theory (cont.)
• The universe was a tiny point that contained
all the energy and matter of the universe.
• The universe began to expand rapidly
and cool.
12.3 Galaxies
The Expanding Universe and
the Big Bang Theory
• The universe was too hot to form elements
for several hundred thousand years.
• The universe consisted of radiation and
subatomic particles.
• As the universe cooled, hydrogen and
helium atoms formed.
12.3 Galaxies
The Formation of Galaxies
• Galaxies began forming several hundred
million years after the Big Bang.
• Clouds of hydrogen and helium possibly
became more dense in some regions.
12.3 Galaxies
The Formation of Galaxies (cont.)
• The dense regions began to clump and
form stars.
12.3 Galaxies
Dark Matter and Dark Energy
• Scientists can calculate how much mass
the universe should contain by the way
galaxies move through space.
• All the matter they can detect added together
is less than the amount needed.
– The missing matter is called dark matter.
– The missing energy needed to explain the
expansion of the universe is called dark
energy.
12.3 Galaxies
Which is the shape of the Milky
Way?
A flat
B elliptical
C irregular
D spiral
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12.3 Galaxies
How old is the universe thought
to be?
A several hundred
thousand years
B 1 million years
C 14 billion years
D 63,000 million years
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12.3 Galaxies
A cluster is a group of ____.
A stars
B solar systems
C galaxies
D planets
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As a star increases in absolute
magnitude, it appears ____ on Earth.
A larger
B hotter
C brighter
D more dense
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A supernova could result in the
formation of a ____.
A supergiant
B neutron star
C red giant
D white dwarf
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Our sun will eventually become
a ____.
A white dwarf
B black hole
C neutron star
D dark planet
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The process by which hydrogen is
changed to helium in the core of a
star is called ____.
A nuclear fission
B nuclear reaction
C nucleolus
D nuclear fusion
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A group of clusters in a galaxy is
called a ____.
A group
B supergroup
C spiral arm
D supercluster
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SCI 4.c
The average distance between Earth
and the Sun is called a(n) ____.
A light-year
B astronomical unit
C angstrom
D solar unit
SCI 2.g
What causes clouds of gas and dust
to form clumps in interstellar space?
A solar winds
B gravity
C electrons
D dark matter
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SCI 4.a
Galaxies have what three shapes?
A cluster, group,
and spiral
B supercluster, cluster,
and group
C spiral, elliptical,
and irregular
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D regular, irregular,
and flat
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SCI 4.d
A star that is blue in color is ____
than a star red in color.
A hotter
B cooler
C larger
D smaller
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SCI 4.d
The light from the Moon was
produced ____.
A on the Moon
B on the Earth
C on the Sun
D none of the above
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