Optical Thickness and Observed Appearance

• optically thin and thick limits
• quiz yourself: sample images
  • supernova remnants in optical: SN 1006, M1, Simeis 147
  • interstellar clouds:Orion Nebula, Barnard 68
  • galaxies in optical: M31 LMC, M87
  • all sky: optical, microwave, near infrared

Blackbody Radiation

Radiation Thermodynamics

• energy density
• pressure

The Planck Spectrum

• basic properties
• Wein's law
• antenna temperature, e.g., as measured by Penzias & Wilson