Big Bang

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Big Bang

• measurement of motion of distant stars shows that
  all matter is moving outward at high velocities
• mathematic calculations suggest that 10-20 Ba the
  existing universe exploded from a "singularity"
  a point of infinite density and temperature
• the initial explosion produced vast clouds of
  hydrogen and helium gas

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Formation of Galaxies

• within each cloud, gravitation pull caused the
  gas to contract into swirling masses
  (protostars), eventually becoming stars and
  groups of stars (galaxies)?
• The Milky Way galaxy formed around 15 Ba some of
  the stars date back to this age
• around 99 of the mass of the universe is
  hydrogen and helium around 1 is heavier matter
  formed during the evolution and break up of stars

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Birth of Stars

• stars range in temperature, from M (red, low
  temp.) to O (blue, high temp.).
• our sun in classified as G (intermediate temp.,
  yellow)?
• stars are initially created through gas
  contraction, which causes nuclear fusion
  (hydrogen to helium)?
• continuing fusion allows stars to release
  enormous amounts of radiant energy

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Aging of Stars

• stars remain in this state for billions of years
  (middle size stars) or millions of years (massive
  stars).
• when hydrogen has been mostly converted to
  helium, stars expand, becoming red giants (with
  helium cores), or red supergiants (with carbon
  cores)?

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Hertzsprung-Russell Diagram

• The H-R diagram plots the relation between mass,
  temperature, and luminosity for stars in the
  active phase of nuclear fusion (90 the duration
  of a star's existence)
• Following this they become less hot, less
  luminous, and less massive

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Death of Stars

• middle size stars
• mantles of hot gas are thrown off, forming
  ejection nebula
• a white dwarf forms at the center
• massive stars
• fuse to an iron core, followed by a catastrophic
  supernova explosion (2-3 times a century in our
  galaxy)?
• the remaining core of supernovae, can implode
  into a black hole from which no matter or even
  light can escape

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Nebulae

• Emission Nebulae clouds of high temperature gas,
  energized by ultraviolet light from a nearby star
• Reflection Nebulae clouds of dust which reflect
  the light of nearby stars
• Dark Nebulae clouds of dust which block light
  from whatever is behind.
• Planetary (Ejection) Nebulae shells of gas
  thrown out dying middle sized stars
• Supernova Remnants explosion of a supergiant
  star

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Figure 2.1
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Evolution of the Solar System

• our solar system formed around 4.6 Ba from a
  swirling cloud of gas and dust (tiny grains of
  ice, silicates, and metals)?
• the sun formed in the center composed mainly of
  hydrogen, releasing radiant energy as hydrogen
  fuses to helium

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Formation of Planets

• within the rings of gas surrounding the sun,
  solid particles became cemented into
  planetesimals (1 km or so in diameter),
  eventually coalescing into planets
• within planets, radioactive decay caused
  convection (rising of hot, less dense materials),
  giving rise to volcanic eruptions
• over time, separation by weight occurred iron
  sank to form a core, surrounded by less dense
  silicate or hydrogen mantles and gaseous
  atmospheres

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Our Solar System
Figure 2.1
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Inner and Outer Planets

• the 5 "outer planets" (Jupiter, Saturn, Uranus,
  Neptune, Pluto) retain the initial
  hydrogen/helium atmospheres
• in the 4 "inner planets" (Mercury, Venus, Earth,
  Mars) the initial atmosphere was lost, replaced
  via emission of volcanic gases
• Venus is surrounded by a dense atmosphere of
  mainly CO2 Mars has a very thin atmosphere, also
  mainly CO2, Mercury has almost no atmosphere

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Asteroids and Comets

• between the inner and outer planets lies a belt
  of asteroids, formed from a fifth ring of rocky
  planetesimals that failed to coalesce
• beyond the outer planets lie numerous comets,
  consisting mainly of gaseous planetesimals
• if captured by the gravitational pull of a
  planet, a comet can be drawn closer to the sun
• the gases begin to vaporize, leaving behing a
  trail of dust

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Satellites and Meteorites

• satellites (such as the moon) form when a
  planetesimal is attracted by the gravitational
  pull of a planet, but not so strongly as to cause
  a collision
• meteorites asteroids and comets arriving on a
  planet or satellite, may produce large impact
  craters
• on planets with adequate atmospheres most
  meteorites burn up in transit

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