THE%20SUN

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THE SUN

• Our source for light, heat and (nearly all)
  energy on the earth.

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The Sun Our Prototype Star

• We know much more about it than any other star
• We describe all other stars in terms of it
• So you MUST memorize its key properties

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Solar Properties

• Mass M? 1.989 x 1033 g 2.0 x 1030 kg
• Radius R? 6.96 x 1010 cm 7.0 x 105 km
• Surface (photospheric) temperature,
  T? 5760 K 9900 F
• Luminosity L? 3.9 x 1033 erg/s 3.9 x 1026 W
• Other important facts to memorize
  Central temperature, Tc 1.5 x
  107 K Central density, ?c 160 g cm-3
  Mean density, ??? 3M?/4?R?3
  1.4 g cm-3

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THE SOLAR INTERIOR

• The innermost 20 by radius, or about 0.8 by
  volume, is the NUCLEAR ENERGY GENERATING ZONE.
  Essentially all of the sun's power is produced by
  fusion reactions in the solar core, in the region
  where the temperature exceeds 6 million K.
• Energy is carried by high energy (?-ray X-ray)
  photons. They scatter or are absorbed every cm or
  so, but their descendants of much lower energy
  eventually emerge from the sun's photosphere.
• These photons stream to us as the visible, IR and
  UV solar radiation that drives the earth's
  climate and provides the root source (via
  photosynthesis) of nearly all energy used on
  earth.

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Pop Quiz 2

• Put away all books, papers, computers, etc.
• Take out a sheet of paper.
• 1- Print your name (1).
• 2- List the seven bands of the electromagnetic
  spectrum in order, starting from that with the
  longest wavelength (6).
• 3- Write down the mass and radius of the Sun (4).
  Dont forget units!

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A Solar Slice
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Energy Transport Zones

• THE RADIATIVE ZONE extends from about 0.2 R?