California Institute of Technology 10.4m Submillimeter Telescope (CSO)

Also known as the Caltech Submillimeter Observatory, this telescope received its first light in 1986 and was shuttered in 2015. Observations of submillimeter waves of light during its lifespan helped in our understand of the formation of galaxies and the chemistry of star formation. It also helped detect heavy water on comets, providing insight into their composition. The facility will be dismantled and removed from the summit over the next several years.