Mauna Kea Observatory on Mauna Kea, Hawaii, USA. One of the two American Keck dome telecopes is on the right and the Japanese Subaru telescope is on the left. The shadow of Mauna Kea against the clouds is in the background. The Subaru telescope is a 8.3 metre optical-infrared telescope. The optical Keck telescope has a 10 metre diameter mirror, which can be used together with the other Keck telescope (not seen) to provide more detailed images. Mauna Kea is a dormant 4200 metre high volcano, which has several telescopes on its summit.