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Chapter 14

Chapter 14

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PHYS 183
Tracy Webb

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PHYS 183 – The Milky Way Inside and Out – Tracy Webb Winter 2013 14: Our Star 14.1 A Closer Look at the Sun  theory that it is a lump of burning coal/wood o calculations show burning couldn’t account for huge output of energy th  gravitational/Kelvin-Helmholtz contraction: suggested in late 19 century that sun generates energy by slowly contracting in size o shrinking gas cloud heats up as gravitational potential energy of particles is converted into thermal energy as gas moves inward o contraction would have been unnoticeable to 19 century astronomers o showed the sun shining for 25 million years  earth far older than this  sun converts mass into energy through process of nuclear fusion o requires extremely high temperatures & densities  found in core of sun o maintains conditions through natural balance between gravity pulling inward & pressure pushing outward  called gravitational equilibrium o pressure increases with depth which makes gas hot & dense which is also heated by the energy released in fusion  maintains pressure  sun born 4.5 billion years ago from collapsing cloud of interstellar gas  contraction released gravitational potential energy (some radiated away, some stayed inside, increasing temperature & pressure) o when nuclear fusion capable, energy generation in interior balanced with energy lost in radiation  balance stabilized size of sun  sun is ball of plasma  gas with many ionized atoms due to high temperature  basic properties of sun o made from H and He o radius under 700 000 km 30 o mass is about 2 x 10 kg o entire sun doesn’t rotate at same rate  equator rotates in 25 days, poles rotate in 30 days 26 o power output/luminosity = 3.8 x 10 watts  solar wind: stream of charged particles continually clown outward in all directions from the sun o helps shaped magnetospheres of planets o blows back material that forms plasma tails of comets  corona: outermost layer of sun’s atmosphere o temperature about 1 million K o emits most of the sun’s x rays o density very low  chromosphere: middle layer of the solar atmosphere & region that radiates most of the sun’s ultraviolet light o temperature about 10 000 K  photosphere: lowest layer of the atmosphere; visible surface of the sun o temperature about 6000 K o where you find sunspots & region of intense magnetic fields PHYS 183 – The Milky Way Inside and Out – Tracy Webb Winter 2013  convection zone: where energy generated in solar core travels upward, transported by rising of hot gas & falling of cool gas (convection) o cause of the sun’s seething, churning appearance o lots of turbulence  radiation zone: energy moves outward primarily in form of photons  core: source of sun’s energy (will take a few hundred thousand years to reach surface) 14.2 The Cosmic Crucible  nuclear f
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