The Caltech Submillimeter Observatory (CSO) was a 10.4-meter (34 ft) diameter submillimeter wavelength telescope situated alongside the 15-meter (49 ft) James Clerk Maxwell Telescope (JCMT) at Mauna Kea Observatories. Beginning in 1986, it was engaged in submillimeter astronomy of the terahertz radiation band. The telescope closed on September 18, 2015.
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