Hertzsprung-Russell diagram A graph used to plot where stars

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The Universe

• Chapter 14

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The night sky

• Sky observations date to ancient civilizations
• Stonehenge was built in England for observing the
  sky.

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The differences between stars and planets

• Stars
• Appear as point sources that produce their own
  light.
• They appear to move counter-clock relative to
  Polaris our north star
• Twinkle from atmospheric turbulence
• Distance measured in light years (ly) 9.5x1012
  km/yr or 6x1012mi/yr.
• Planets
• Visible by reflected light

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The celestial sphere

• Celestial objects are projected onto imaginary
  sphere around the Earth
• Celestial equator, is the Earths equator
  projected into the sky.
• Altitude angle and azimuth angle determine
  location on this celestial sphere. They act like
  latitude and longitude lines in space.
• Objects appear to rotate about north/south poles

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Birth of a StarProtostar Phase to Main Sequence
Star

• Gravitational collapse of a gigantic cloud of
  mainly hydrogen gas and dust produces a Protostar
  .
• When density, temperature and pressure increases
  until conditions are right for nuclear fusion a
  star is born.
• Temperatures of 10 million K must be reached for
  hydrogen atoms to be fused to other hydrogen
  atoms thus causing nuclear fusion.

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Once fusion occurs and a star is born -

• The gigantic cloud of gas and dust spends
  billions of years calmly shinning while it fuses
  hydrogen nuclei in the core.
• When inward force of gravity equals outward
  pressure of fusion stars enter the main sequence
  where it will remain most of its life.
• Life not observed but theoretically based on
  knowledge of nuclear reactions.
• Predicted outcomes seem to agree with
  observations of stars today.

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Star Model

• Core
• Very hot
• Nuclear fusion
• Radiation zone
• Diffuses outward over millions of years
• Convection zone
• Material rising from the interior, cooling, and
  sinking
• Visible surface of star
• Sun surface temp. 5,800 K

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Hertzsprung-Russell diagram

• A graph used to plot where stars are in their
  life cycle.
• Stars do not just stay in one star stage of the
  HR diagram
• They enter different stages as their masses and
  temperatures change due to fusion.

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Star types

• Hertzsprung-Russell diagram
• Plots absolute magnitude and temperature
• Each dot star
• Stars grouping
• Main sequence stars
• Red giants
• Novas
• White dwarfs
• Cepheid variables

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Stellar evolution - summary
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Lifetime of Our Star, the Sun

• Converts 1.4x1017 kg of matter to energy each
  year
• About two thousand seven hundred 6000 lb SUVs!
• Born 5 billion years ago, should last another 5
  billion years.
• Lifetime depends on mass
• Our suns fate could be a white dwarf because of
  its size.
• Less massive stars have longer lifetimes
• More massive stars have shorter lifetimes

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Brightness of stars

• Differences in stellar brightness is caused by-
• The amount of light produced by star
• The size of star
• The distance to the star

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• Absolute magnitude vs Apparent Magnitude
• Example- Our Sun
• Absolute magnitude 4.8
• Determined by a standard distance
• Apparent magnitude -26.7
• How objects looks compared to other objects
  around it. The more negative the number the
  brighter the object.

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Star temperature(related to color of star)

• Colors appear as red, yellow, bluish white
• Color related to surface temperature
• Red cooler stars
• Blue hotter stars
• Yellow in between (Sun)
• Classification scheme
• Based on temperature hottest to coolest
• O, B, A, F, G, K, M

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Blow-off- outer layers of stars form ring like
structures called planetary nebulae
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Death of Massive Stars Produces Supernovas

• Supernova
• Star collapses
• Elements beyond iron created in explosion and
  distributed throughout Universe
• More mass more gravitational contraction and
  heat
• Critical temperature 600 million K for
  supernova

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Depending on mass that remains after the
Supernova-

• Neutron star
• Remaining core between 1.4 and 3.0 solar masses
• Gravitational pressure fuses protons and
  electrons into neutrons
• Pulsar rotating, magnetized neutron star
• Black hole
• Remaining core greater than 3 solar masses
• Gravitational collapse overwhelms all known
  forces
• Even light cannot escape the dense, compact object

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Most stars exist in groups.

• Binary systems
• Two gravity bound stars
• Most stars are in binary pairs, not ours
• Star clusters
• Tens to hundreds of thousands or more gravity
  bound stars
• Often share a common origin

• Galaxies
• Basic unit of the Universe
• Billions and billions of gravitationally bound
  stars
• Larger scale still
• Clusters of galaxies
• Super clusters of galaxies
• Billions and billions of galaxies!

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Early Astronomers

• Galileo- used telescope to look at Milky Way and
  determined it was made up of a multitude of stars
  in about 1630.

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The Milky Way

• Visible as a band in night sky.
• Billions of stars
• Spiral structure

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Wide angle view of the Milky Way
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Other galaxies

• Our nearest neighbors - the Local Group
• Dwarf galaxies
• 1,000 light years across
• Nearest dwarf is disrupted gravitationally by the
  Milky Way
• Andromeda
• 2 million light years away
• Very similar to Milky Way
• Classification scheme (Hubble)
• Elliptical, spiral, barred and irregular

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Spiral Galaxies
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Barred Spiral Galaxies
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Irregular galaxies
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• Possible suggestion of how
• God created the Universe is
• the Big Bang Theory

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The life of a galaxy theorized by scientists

• Big Bang Theory
• Universe evolved from an explosive beginning
  about 13.7 billion years ago.
• Raisin bread theory
• Supporting evidence
• Microwave background radiation
• Large scale expansion
• Abundances of elements
• Diffuse cosmic background radiation
• The end
• Expansion forever or the big crunch?