Implications of H-alpha Observations for Studies of the Cosmic Microwave Background

We summarize the relationship between the free-free emission foreground and Galactic H-alpha emission. H-alpha observations covering nearly the entire celestial sphere are described. These data provide a template to isolate and/or remove the effect of Galactic free-free emission from observations of the cosmic microwave background. Spectroscopy and imaging provide two complementary methods for measuring the H-alpha emission. Spectroscopy is favored for its velocity resolution and imaging is favored for its angular resolution. With templates of the three dominant foregrounds, namely synchrotron, thermal dust, and free-free emissions, it may be possible to quantify the location and the brightness of another foreground such as that from rotating dust grains.