millimeter astronomyA branch of radio astronomy covering the wavelength range from 1 to 10 millimeters approximately. When studies began in the late 1960s it was the highest frequency range, 30–300 gigahertz, in which radio astronomy could be carried out. Submillimeter astronomy has since become feasible. Both millimeter and submillimeter wavelengths are ideal for observations of giant molecular clouds. A large variety of molecules form at the high densities in the clouds. The spectral lines emitted by the molecules are mainly in the millimeter and submillimeter range, and give information on chemical composition, relative abundances of isotopes, chemical reactions, and temperatures, densities, and velocities in the clouds (see also molecular-line radio astronomy).
Millimeter wave instrumentation – usually parabolic radio dishes plus line receivers – is similar to that used for submillimeter astronomy. One example is the James Clerk Maxwell Telescope (JCMT) on Mauna Kea, Hawaii.