Submillimetre

The submillimetre, or submillimeter, is a portion of the electromagnetic spectrum with wavelengths shorter than the millimetre and longer than the far infrared. It covers roughly 0.3 to 1 millimetre in wavelength, corresponding to frequencies around 0.3 to 1 terahertz. Spelling varies by region: submillimetre is common in British English, while submillimeter is used in American English.

In astronomy and atmospheric science, submillimetre observations probe cold dust and molecular gas in the interstellar medium, the early stages of star formation, and distant, dust-enshrouded galaxies. Continuum emission from dust at tens of kelvin is prominent; molecular rotational lines, notably carbon monoxide, appear in this range and provide diagnostic information about physical conditions and motions.

Observations at these wavelengths face challenges from Earth's atmosphere, especially water vapor, which absorbs many submillimetre windows. This drives the use of high-altitude, dry sites or space-based and airborne instruments. Detectors include sensitive bolometers and heterodyne receivers. Large interferometric arrays, such as the Atacama Large Millimeter/submillimeter Array (ALMA) and the James Clerk Maxwell Telescope (JCMT), enable high-resolution mapping of star-forming regions, protoplanetary disks, and distant galaxies.

The submillimetre band lies between the far-infrared and radio/microwave regions, complementing other infrared and radio observations. It has been central to advances in understanding star formation, the interstellar medium, and galaxy evolution, and continues to be a key window on the cold universe.