Chapter 19 – Stars, Galaxies and the Universe

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Chapter 19 Stars, Galaxies and the Universe

• Stars A ball of hot gas undergoing fusion to
  produce heat, light and other forms of radiation.
• Color can be used to determine the temperature
  and composition of a star Blue Hot Red Cool
• Spectrum the component colors of light when
  passed through a prism. Used to determine a stars
  composition.
• Spectrograph An instrument used to analyze star
  light.
• Emission Lines Colors given off by the hot
  gases of a star and can determine the elements
  present in that star.

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• Absorption Spectrum The black areas of a stars
  spectrum that represents the light that gets
  absorbed by that stars atmosphere.
• Stars are classified by how hot they are.
  O-class stars are the bluest the
  hottest. M-class stars are the
  reddest the coolest. Astronomers classify stars
  by their brightness or magnitude. Positive
  numbers are dim stars and negative numbers are
  bright stars.
• Apparent Magnitude How bright a star appears to
  be when viewed from the Earth.
• Absolute Magnitude The actual brightness of
  star calculated at a distance of 32.6 light years
  from the Earth.
• Our sun (Sol) has an absolute magnitude of 4.8
  but an apparent magnitude of -26.8 because it is
  so close to us.

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• Distances to the stars
• A light year is the unit of measurement
  astronomers use and is the distance that light
  travels in a vacuum in one year (approx.
  9,500,000,000,000 km.). Measurements of stellar
  distances are based on the apparent movement of a
  star when viewed from the Earth and is called the
  parallax effect. To view a parallax shift, a
  telescope must view a star from two different
  locations and then the star is compared to other
  stars in the background image.
• The stars, just like the sun and the moon, appear
  to move across the night sky due to the rotation
  of the Earth. However, in reality, the stars are
  actually shifting very slowly so that in time,
  the constellations will not appear as they do
  now.

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• The Life Cycle of Stars
• Early Life A stars begins life as a ball of gas
  dust. Gravity begins to draw everything in
  towards the center creating a denser mass which
  increases friction hence temperature. The
  temperature continues to increase until its hot
  enough for fusion to occur then the star begins
  to glow.
• Mid-Life The star slowly consumes its hydrogen
  fuel.
• The End The fuel is used up and the star begins
  to cool, enlarging first then shrinking or it
  could blow itself apart distributing its elements
  into the universe where it could possibly
  recombine into a new star.

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Types of Stars

• Main Sequence Stars A typical star in the
  middle of its life.
• Red Giant A stars that has enlarged and cooled
  as the result of its using up all of its
  hydrogen. The core shrinks and the atmosphere
  expands to become 10 times larger than our sun or
  a super-giant expands to 100 times larger.
• White Dwarfs A small, hot star that is actually
  the remaining core of a red giant or super-giant
  once its gases have blown away in a planetary
  nebula. There is no hydrogen remaining and the
  star is at the end of its life.

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Hertzsprung-Russell (H-R) Diagrams

• A graph that shows the relationship between a
  stars temperature and its absolute magnitude
  (brightness). Used to study the lifespan of a
  star. A stars temperature will determine its
  color. The brightest stars are at the top left
  and the dimmest stars are at the bottom right of
  the H-R diagram. The diagonal pattern where most
  stars lie is called the Main Sequence. Our sun is
  a main sequence star.

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Old Stars

• Supernovas A gigantic explosion in which a
  massive star collapses and throws its outer
  layers of gas into space. A supernova will result
  in a black hole or a neutron star.
• Neutron Star A star with such a huge
  gravitational pull, that the electrons protons
  of its component elements are crushed into
  neutrons.
• Pulsar A rapidly spinning neutron star that
  emits rapid radio pulses picked up as clicks on
  radio telescopes.
• Black Hole A star that collapses its center so
  completely all that is left is a hole in
  space/time. A black hole is so gravitationally
  massive that even light cannot escape.

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Galaxies

• A large grouping of stars, gas and dust that are
  classified by their shapes spiral, elliptical or
  irregular.
• Our galaxy is called the Milky Way and is a
  spiral galaxy.
• Spiral galaxies have a dense, bulging center with
  arms spiraling out composed of gas, dust and
  stellar nurseries.
• Stellar nurseries are found in some nebulae, a
  few elliptical galaxies and in the arms of spiral
  galaxies.

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• Nebula A cloud of gas and dust where new stars
  form and old ones have exploded.
• Globular Cluster A group of tightly packed,
  older stars that looks like a ball. These form a
  halo surrounding the central bulge (Shapley
  Center) of a spiral galaxy and are also common
  near elliptical galaxies.
• Open Cluster groups of closely grouped stars
  found in the spiral discs of galaxies.
• Astronomers need to look at the farthest objects
  in the universe to help them determine what early
  galaxies looked like.
• Quasars one of the most distant objects that
  are very bright and powerful releasing energy at
  a very high rate. A quasar is actually an active
  black hole. The energy released is a result of
  too much matter falling in at a high rate of
  speed. The U.S. Air Force calibrates the position
  of its G.P.S. satellites to 350 distant quasars
  because the do not move relative to the Earth.

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Cosmology

• The study of the origin, structure and future of
  the universe. To determine the age of the
  universe, cosmologists measure the distance from
  the Earth to various galaxies.
• The Big Bang Theory States that all of the
  matter in the universe was once a microscopic
  point of infinite density that exploded approx.
  13.7 billion years ago. This matter at first
  formed subatomic particles, then atoms and
  eventually nebulae, stars and continues to expand
  today. Cosmic background radiation fills the
  farthest points of the universe and continues to
  expand outwards with the universe. Scientists
  believe that the universe will always exist and
  continue expanding.