|Location(s)||Mauna Kea, Hawaii County, US|
|Organization||California Institute of Technology|
|Altitude||13,570 ft (4,140 m)|
|Wavelength||1,300, 350 μm (230, 860 GHz)|
|Telescope style||radio telescope|
|Diameter||10.4 m (34 ft 1 in)|
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. It was engaged in submillimetre astronomy, of the terahertz radiation band. The telescope closed on September 18, 2015. As of April 2019, the telescope is set to be dismantled and its site remediated in the near future as part of the Mauna Kea Comprehensive Management Plan.
The CSO and JCMT were combined to form the first submillimeter interferometer. The success of this experiment was important in pushing ahead the construction of the Submillimeter Array and the Atacama Large Millimeter Array interferometers.
In order to get a permit to build the Thirty Meter Telescope project on Mauna Kea, the University of Hawaii had to commit to closing and dismantling three existing observatories on the mountain. The three chosen were the CSO, the UKIRT, and the Hoku Keʻa telescope. Two additional telescopes must also be removed by 2033, but those have not been selected as of 1 April 2019.
On April 30, 2009, Caltech announced plans to decommission the CSO, transferring ongoing research to the next-generation Cerro Chajnantor Atacama Telescope (CCAT) in Chile. The plans called for CSO to be dismantled, beginning in 2016, with its site returned to a natural state by 2018. Delays in the environmental assessment and permitting processes have led to postponement of the telescope removal. On 24 January 2019, Robert McLaren, the interim Director of the University of Hawaii Institute of Astronomy, gave an update to state lawmakers and suggested the permitting will be accomplished in 2019 with dismantling and removal taking a year or less.
- "Third Maunakea observatory set for decommissioning". University of Hawaii News. University of Hawaii. Retrieved 3 December 2015.
- "VIDEO: Update On Taking Telescopes Off Mauna Kea". www.bigislandvideonews.com. Retrieved 2019-04-02.
- "Caltech Submillimeter Observatory in Hawaii to be Decommissioned" (Press release). Caltech.edu. April 30, 2009. Archived from the original on June 10, 2010. Retrieved December 22, 2010.
- McGuire, Brett A.; Carroll, P. Brandon (31 October 2017). "The Final Integrations of the Caltech Submillimeter Observatory". Research Notes of the AAS. 1 (1): 4. arXiv:1711.09145. Bibcode:2017RNAAS...1a...4M. doi:10.3847/2515-5172/aa9657. ISSN 2515-5172.