From Last Time: Atmospheric Transmission

• transmission spectrum over full EM spectrum
• spectrum in visible and IR

The 21 cm Line

• physics: hyperfine splitting
• awesome examples:
  • the sky in 21 cm; disk map: velocity-colored
  • galaxy M31 in optical and in 21 cm + thermal IR
  • galaxy M33 in optical and in 21 cm
  • galaxy rotation curves at 21 cm
  • cosmic 21 cm radiation evidence for monopole and fluctuations; LOFAR, SKA