Molecular Clouds (2) ...
Dust is particularly abundant in the disks of spiral galaxies, where most star formation takes place. The
adjacent image shows a spiral galaxy in Orion.
The dark band lying in the plane of the disk is dust.
Detecting Molecular Clouds
Molecular clouds, which are the origination of many stars, are very difficult to study because they are
primarily composed of molecular hydrogen at temperatures only about 10 degrees above absolute zero. Since
hydrogen is virtually invisible under those conditions with normal detection methods, 99 percent or more of a
molecular cloud cannot be seen with standard methods.
