High Quality Content by WIKIPEDIA articles! The James Clerk Maxwell Telescope (JCMT) is a submillimetre-wavelength telescope at Mauna Kea Observatory in Hawaii. Its primary mirror is 15 metres (16.4 yards) across: it is the largest astronomical telescope that operates in submillimetre wavelengths of the electromagnetic spectrum (far-infrared to microwave). Scientists use it to study our Solar System, interstellar dust and gas, and distant galaxies.