 BSUBM by L-L-I-M-E-T-R-E of astronomy, sub-millimeter of astronomy or sub-millimeter of astronomy. C-spelling differences is the branch of observational astronomy that is conducted at sub-millimeter wave lengths i.e., Terahertz radiation of the electromagnetic spectrum. Astronomers place the sub-millimeter waveband between the far infrared and microwave wavebands, typically taken to be between a few hundred micrometers and a millimeter. It is still common in sub-millimeter astronomy to quote wave lengths in microns, the old name for micrometer. In sub-millimeter observations, astronomers examine molecular clouds and dark cloud cores with a goal of clarifying the process of star formation from earliest collapse to stellar birth. Sub-millimeter observations of these dark clouds can be used to determine chemical abundances and cooling mechanisms for the molecules which comprise them. In addition, sub-millimeter observations give information on the mechanisms for the formation and evolution of galaxies.