Download Unit 8 Chapter 30 Stars, Galaxies and the Universe

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Unit 8 Chapter 30
Stars, Galaxies and the Universe
Section 1 Characteristics of Stars
A star is a ball of gases that give off a tremendous amount of energy. As
with our “star” all star’s energy comes from nuclear fusion.
Another cool thing about stars is that they come in colors.
Analyzing Star Light
Astronomers use a spectroscope to bend the light of the stars and look at
the properties of them.
Composition of Stars
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Temperature of Stars
The surface temperature of the star will indicate the color. Hot stars are
_____________________________. The in between are _____________.
The Size and Mass of Stars
Sizes will vary as with any type of object. Our sun is an average size and
mass.
Stellar Motion
There are two kinds of motion an object will have
Actual motion – _______________________________________________
Apparent motion – _____________________________________________
Apparent Motion
Apparent motion is the motion that the stars appear to make in the sky
when in actuality it is the earth that is moving.
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Circumpolar stars
They are the stars that seem to revolve around the North Star (Polaris).
Because Polaris is near our axis point. Circumpolar stars are stars
that move around Polaris and are always visible in the Northern
Hemisphere
Actual Motion
First, they move across the sky, which can be seen only for the closest
stars. Second, they may revolve around another star. Third, they either
move away from or toward our solar system.
Don’t forget – _____________________________________________
Distances to Stars
Astronomical Unit – A.U.
Light Year
Parallax
Stellar Brightness
Brightness of Stars:
Around 120 BCE, a Greek astronomer named Hipparhus developed a
system to classify a stars brightness. He used about 850 of the stars that
he studied. The brighter stars were #1, dimmest were #6. Years later
Ptolemy expanded the scale to include 1000 stars.
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Apparent Magnitude
_________________________________________________. This
depends on how bright the star is and how far it is from the Earth. The
scale is from 0 to 6, 0 being the brightest. If a star is brighter than a
magnitude 0, you use a negative value.
0
1
2
3
4
Brightest
5
6
Faintest
Each number is a multiple of 25 times higher than the one before.
Example, A magnitude 1 star is 25 times brighter than a magnitude 2 star.
It is 25 X 25 or 625 times brighter than a magnitude 3 star.
Absolute Magnitude
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Our sun would be a 4.8, average star, Rigel has an Absolute Magnitude of 6.4 which makes it appear brighter than most stars.
Remember, all stars are not the same distance away, therefore, a faint star
may really be very bright if it were closer.
Variable Stars
Stars that change their brightness in cycles. The cycles can be short
(days) or long (years). This is caused by expansion (cooler/dimmer) or
contraction (hotter/brighter).
Section 2 Stellar Evolution
Because a typical star exists for billions of years, astronomers will never be
able to observe one star throughout its entire lifetime. Instead, they have
developed theories about the evolution of stars by studying stars in
different stages of development.
Classifying Stars
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Hertzsprung-Russell Diagram
Danish astronomer Ejnar Hertzsprung and American astronomer Henry
Norris Russell developed the diagram independently. This scale graphs all
stars by temperature and luminosity. See ESRT
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Main Sequence:
Most of the stars in the galaxy fall into this category. They are very
stable stars that have long lives.
Luminosity
_____________________________________. This depends on the Size
and Temperature. If sizes were equal, a hotter star would be more
luminous than a cool one. If temperature were the same, the larger ones
would be more luminous.
Star Formation
It is believed that stars probably formed in similar ways. The theory is that
a cloud of dust (a nebula) contracts with most of the material going to the
center to form a star.
The dust is mainly Hydrogen (99%) with other elements and compounds
like silicon carbide, graphite diamonds and nitrogen. The dust cloud most
likely came from an exploded star. As the cloud shrinks materials become
hotter because of the compaction.
Protostars
A Protostar is a warm glowing mass.
The Birth of a Star
If the contraction continues hydrogen fusion may occur.
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The Delicate Balancing Act
The Main Sequence Stage
Stage one – new star that has used up about 5% Hydrogen
The second and longest stage in the life of a star is the mainsequence
stage. During this stage, energy continues to be generated in the core of
the star as hydrogen fuses into helium.
Leaving the Main Sequence
Stage 3: After a star is formed it continues hydrogen fusion. Eventually the
hydrogen is used up. This triggers fusion on the outside of the core. The
star expands when the core temperature becomes hot enough; it starts to
fuse other elements. The gases begin to blow away in bursts until a fierce
hot core is left (white dwarf).
Giant Stars
They are large cool stars with diameters 10 to 100 times larger than our
sun. Ex. Aldebaran and Arcturus
Red Giants:
When all the fuel (H) is used up the star starts to collapse again. This gets
the star hot again. Helium fusion begins. The star expands further and is
brighter than before.
Ex. Betelgeuse in Orion’s constellation
Super Giants
They are bright, hot stars whose diameter is more than 100 times larger
than our sun.
Ex. Blue-White Rigel and White-Yellow Canopus
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The Final Stages of a Sun Like Star
In the evolution of a medium-sized star, fusion in the core will stop after
the helium atoms have fused into carbon and oxygen. With energy no
longer available from fusion, the star enters its final stages.
Planetary Nebula
Planetary Nebula is left (a glowing halo of gases that 18th century
astronomers thought they looked like disks of planets).
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White Dwarfs
After a long while there is no more fuel left for the star, it collapses onto
itself. It becomes very small, earth size and only faintly glows until it
becomes cold and dark.
Novas and Super Novas
They are near the end of their lives as stars. If it flares up again, it
becomes a Nova (new star) and can burn for a while longer.
Super Nova: The center core of huge stars is mainly made up of heavy
metals (U, Pb, Fe, Ni). When all of the fuel is used up the collapse of these
metals is very rapid. The star can not contain all the material, it just
EXPLODES. The death takes millions of years, but when it gets to the core,
it can take a few weeks to a few months. This becomes the source
material for new stars/solar systems.
Neutron Stars
Stars that contain about 8 or more times the mass of the sun do not
become white dwarfs. After a star explodes as a supernova, the core may
contract into a very small but incredibly dense ball of neutrons, called a
neutron star. A single teaspoon of matter from a neutron star would have a
mass of 2 × 1030 kilograms (a 2 followed by 30 zeroes). A neutron star that
has more mass than the sun may have a diameter of only about 20 km but
may emit the same amount of energy as 100,000 suns. Neutron stars
rotate very rapidly.
Pulsars
Neutron stars that are extremely dense and small are formed from super
novas. This causes a fast rotation. The fast rotation and magnetic fields
causes radio waves to be sent from the star in pulses.
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Black Holes
When a really large neutron star collapses to the point where the mass is
infinitely small (all the mass of a star in a Point). The gravity is so strong
that light cannot escape. These are the most massive objects in existence.
In September 2000 the scientists discovered evidence concerning the
existence of a black hole in the center of our galaxy.
Section 3: Star Groups
Most stars we see are at least 100 light years away. Most seem to be
individual stars; however, they really belong to larger groups.
Constellations
By using a star chart and observing carefully, you can identify many star
groups that form star patterns or regions. Although the stars that make up
a pattern appear to be close together, they are not all the same distance
from Earth. In fact, they may be very distant from one another.
Dividing up the Sky
In 1930, astronomers around the world agreed upon a standard set of 88
constellations. The stars of these constellations and the regions around
them divide the sky into sectors. Just as you can use a road map to locate
a particular town, you can use a map of the constellations to locate a
particular star.
Multiple Star Systems
Binary Stars are pairs of stars that revolve around each other. There are
some that are more than two.
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Star Clusters
Sometimes, nebulas collapse to form groups of hundreds or thousands of
stars, called clusters. Globular clusters have a spherical shape and can
contain up to one million stars. An open cluster is loosely shaped and rarely
contains more than a few hundred stars.
Galaxies
Galaxy:
Billions of stars rotating around each other or a central point (black hole?).
There are billions of galaxies out there.
Ours is called the Milky Way
Distances to Galaxies
By comparing the absolute magnitude to the apparent magnitude of stars,
Astronomers can judge the distances to other galaxies.
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Types of Galaxies
Spiral galaxies are pin wheel shaped with dense central core with spinning
arms extruding out from the core.
Elliptical are circular in shape with most stars in the core. It does not have
arms.
Irregular galaxies are the least common with no star pattern; they are
scattered randomly
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The Milky Way
The Milky Way galaxy is a spiral galaxy in which the sun is one of hundreds
of billions of stars. Each star orbits around the center of the Milky Way
galaxy. It takes the sun about 225 million years to complete one orbit
around the galaxy.
The Local Cluster is a group of 30 of the nearest galaxies
Quasars
Quasars are believed to be galaxies in early stages of development. They
are very bright, very far away. radio waves Tremendous come from them.
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Section 4 The Big Bang Theory
Cosmology is the study of the universe. Cosmologists are the specialized
scientists who study how the universe was formed and when.
Hubble’s Observation
In 1929 Hubble discovered that ALL galaxies were RED SHIFTED. This
meant that all galaxies are moving apart. This is major proof for the big
bang theory.
Measuring Red Shift
Hubble found that the spectra of galaxies, except for the few closest to
Earth, were shifted toward the red end of the spectrum. By examining the
amount of red shift, he determined the speed at which the galaxies were
moving away from Earth. Hubble found that the most distant galaxies
showed the greatest red shift and thus were moving away from Earth the
fastest.
The Expanding Universe
By using Hubble's observations, astronomers were able to determine that
the universe was expanding.
A Theory Emerges
It is believed that all the matter in the universe started out in one small
sphere. There was an explosion and all the matter was sent outward. As
it spread out, the material was slowly transformed into the Universe we see
today.
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Cosmic Background Radiation
In 1964 background radiation is detected in space without a stellar source.
This could be the “sound” left over from the big bang. This also supports
the theory.
Ripples in Space
These ripples are irregularities in the cosmic background radiation, which
were caused by small fluctuations in the distribution of matter in the early
universe. The ripples are thought to indicate the first stages in the
formation of the universe's first galaxies.
A Universe of Surprises
Astronomers now think that the universe is made up of more mass and
energy than they can currently detect.
Dark Matter
23% of the universe is made up of a type of matter that does not give off
light but that has gravity that we can detect. Because this type of matter
does not give off light, it is called dark matter.
Dark Energy
Scientists think that it acts as a force that opposes gravity. Because of dark
energy, the universe is not only expanding, but the rate of expansion also
seems to be accelerating.