The_Universe by xiagong0815


									The Universe
   ESCI 1214
    Fall 2006
                        The Sun
• The solar interior
      • Energy source is from nuclear fusion
      • Hydrogen is converted to helium (proton-proton chain). This
        process results in unbelievable amounts of energy
          – One pinhead of hydrogen converted to helium produces more
            energy than burning thousands of tons of coal!

• The photosphere
      • The “Surface” of the sun
      • Not uniform in brightness
      • Granules (size of Texas) are bright, surrounded by darker
      • Up and down motion of gases is a result of convection
               The Sun (cont)
• The Chromosphere
    • Lies just above the photosphere
    • A few thousand miles thick
    • The top contains spicules which are flame-like structures that
      can extend 10,000km into the corona
• The Corona
    • Outermost portion of the solar atmosphere
    • Extends out a million kilometers from the sun
    • The solar wind comes from the corona as a result of a stream
      of protons and electrons that are able to escape the gravity of
      the sun (their speed is greater than the pull of the gravity,
      much like the space shuttle must travel at a rate of 7 mps to
      escape earth’s gravity)
The Sun (cont)
           Properties of Stars
• Stellar Brightness
  – Apparent magnitude refers to the magnitude, or
    brightness, of a star as viewed from earth. The true
    magnitude is the measure of a stars brightness is its
    absolute magnitude
• Stellar Color and Temperature
  – Stars with temperatures over 30,000K are blue,
    between 5000 and 6000K are yellow, and those
    around 3000K are red
• Binary Stars
  – stars that appear as one, but are two when looked at
    closer. The two stars actually orbit one another.
     Idealized Hertzburg-Russell
             Star Types
• Main-sequence stars
  – “ordinary” stars (about 90% of stars)
• Red Giants
  – Very luminous stars (i.e. a star 100 times more
    massive than our sun)
• Supergiants
  – Extremely large stars (i.e. Betelgeuse is 800 times
    more massive than our sun)
• White Dwarfs
  – Very faint stars
Hertzsprung-Russell Diagram and
             Interstellar Matter
• Nebulas (clouds)
  – Concentrations of dust and gas
• Bright nebula
  – Nebula close to a very hot star causing it to glow
• Emission Nebulae
  – Nebulas that consist of hydrogen, absorb uv radiation
    and emit light as a result (sword of Orion)
• Reflection nebulae
  – Nebulas that reflect the light of other stars
• Dark Nebula (not close enough to a bright star)
Horsehead Nebula and Orion
                      Stellar Evolution
• Stellar Evolution
   – Star Birth
       • Stars come from cool interstellar clouds of dust. Gravitational pull begins
         and the clouds contract. Lasts approximately a million years
   – Protostar Stage
       • At this stage, the cloud has contracted and the center is much hotter than the
         outer areas. This stage does not get to the nuclear fusion stage
   – Main Sequence Stage
       • Nuclear fusion takes place, converting hydrogen to helium and releasing
         extreme amounts of energy. Can burn for a few billion years
   – Red Giant Stage
       • The hydrogen core is consumed and begins to contract. Fusion spreads to
         the outer edges and this heating causes the star to grow by hundreds or
         thousands of times the size of its main sequence stage
   – Burnout and Death
       • Low mass, medium mass become white dwarfs and planetary nebulae
       • Massive stars become supernovas
            Stellar Remnants
• White Dwarfs
  – Stars that have collapsed to the point of extremely
    high density. This density occurs when electrons
    move nearer the nucleus and use electrical repulsion
    to keep from collapsing. One spoonful of this material
    could way several tons
• Neutron Stars
  – The remnants of supernova events, the electrons are
    forced to combine with the protons and form neutrons
• Black Holes
  – Even smaller than neutron stars, black holes are
    incredibly dense masses with gravitational forces able
    to devour anything that passes near it
• Spiral
• Barred spiral
• Elliptical
  – 60% of
                             Red Shift
• Red Shift
   – Refers to the shift in wavelength that
     will occur when an object is moving
     towards or away from us (Doppler
     effect). As a car approaches, it
     makes a higher pitch sound, as it
     passes us, it makes a lower pitch
     sound. Light does the same thing,
     except it shifts in the color spectrum
   – As an object moves away from us,
     there is an increase in the
     wavelength. A result of this is for the
     color emitted by this object to “shift”
     to the longer wavelength colors
     (red), hence the term “red shift”
                  Red Shift
• What do we see in space? Virtually all objects in
  space are moving away from us (as evidenced
  by the red shift phenomena)
• What does this mean? Scientists believe this
  means we are part of an ever expanding
  universe. One in which the velocity of the
  objects is higher than the critical point at which
  gravity would bring everything back together
  (remember the space shuttle leaving earth)
            The Big Bang
• The red shift and subsequent theories that
  developed as a result led to the Big Bang
• The Bing Bang holds that the universe
  was a singularity (a dense, hot,
  supermassive ball) that exploded some 15
  billion years ago and set forth the
  expansion we see today

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