Caltech Submillimeter Observatory in the context of Submillimeter Array

The Mauna Kea Observatories have been controversial since the first telescope was built in the late 1960s. Originally part of research begun by Gerard Kuiper of the University of Arizona, the site has expanded into the world's largest observatory for infrared and submillimeter telescopes. Opposition to the telescope from residents in the city of Hilo, Hawaii were concerned about the visual appearance of the mountain and Native Hawaiians voiced concerns over the site being sacred to the Hawaiian religion as the home of several deities. Environmental groups and activists have been expressing concern over endangered species habitat.

The Outrigger Telescopes Project, intended to build from four to six comparatively small telescopes for interferometry, was to surround the Keck telescopes. It was cancelled in 2006, after a court found NASA's Environmental Impact Statement was improperly limited to just the telescope area.

Submillimetre astronomy or submillimeter astronomy (see spelling differences) is the branch of observational astronomy that is conducted at submillimetre wavelengths (i.e., terahertz radiation) of the electromagnetic spectrum. Astronomers place the submillimetre waveband between the far-infrared and microwave wavebands, typically taken to be between a few hundred micrometres and a millimetre. It is still common in submillimetre astronomy to quote wavelengths in 'microns', the old name for micrometre.

Submillimetre observations can be used to trace emission from gas and dust, including the CI, CO, and CII lines. Sources behind this emission include molecular clouds and dark cloud cores, which can be used to clarify the process of star formation from earliest collapse to stellar birth, by determining chemical abundances in dark clouds and the cooling mechanisms for the molecules which comprise them. Other sources include protoplanetary discs, dusty starburst galaxies in the early Universe, immediate environments surrounding AGN, and secondary anisotropies in the cosmic microwave background.