Intensity Mapping with the 21-cm and Lyman Alpha Lines
  The 21-cm and Lyman Alpha lines are the dominant line-emission spectral
features at opposite ends of the spectrum of hydrogen. Each line can be used to
create three dimensional intensity maps of large scale structure. The sky
brightness at low redshift due to Lyman Alpha emission is estimated to be 0.4
Jy/Steradian, which is brighter than the zodiacal light foreground.
