Thermal Radiation: Kirchhoff's Law

• thermal vs blackbody emitters
• example: Cas A X-ray spectrum

Two-Level Systems: Spectral Lines

• spontaneous and stimulated emission
• Einstein coefficients
• spectral line examples
  • ionized hydrogen = HII region
  • the Sun: spectral overview, zoom, continuum and line imaging
• astrophysical masers: AGN NGC 4258, AGB star TX Cam (Gonidakis, Diamond, & Kemball 2013)