What specific feature do astronomers target using radio astronomy to map the distribution of gas clouds?

Answer

The 21-centimeter line emitted by neutral hydrogen gas.

Neutral hydrogen is abundant throughout the galaxy, and its unique, specific radio signature allows astronomers to precisely locate and track these gas clouds.

What specific feature do astronomers target using radio astronomy to map the distribution of gas clouds?
NASAgalaxyastronomyobservationMilky Way