Ch 08-01 The Solar Atmosphere

• Photosphere
  
  • Granules, Granulation
    
    [Granules, roughly of size 1000 km, appear and disappear at a time scale of about 30 minutes.] [play movie]
    
    
    
    
  • Limb darkening
    
    
    
  • Opacity, the degree of being not transparent to photons. It depends on the interaction between matter and photons, i.e., absorption and scattering.
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    It is often defined as κ = nσ/ρ, where n is the number density, ρ is the mass density, and σ is the reaction cross section for the corresponding opacity.
    The optical depth is then defined as τ = αL = ρκL, where α is the absorption coefficient and L is the physical depth. σ and therefore κ and α are strongly frequency dependent.
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  • H^-, opaque to the light, sharp edge
  • Density about 10^-7g/cm³ (about 10^-4 of the air at the see level on Earth)
  • Temperature 5800 K ~ 4400 K
  • Absorption lines, abundance
    
     
• Chromosphere
  
  • Better seen in H_α
    
    
     
  • Spicules
    
     
  • Dominated by emission lines
  • Density about 10^-11g/cm³
  • Temperature 4400 K ~ 25000 K
  
   
• Corona
  
  
  
  • High temperature
    
    
    
  • Corona holes, solar winds (e^-, p, α, etc, about 10¹²g/sec, ~ 10^-14M_⊙/year)