Stability of the Submillimeter Brightness of the Atmosphere above Mauna Kea, Chajnantor, and the South Pole

The summit of Mauna Kea in Hawaii, the area near Cerro Chajnantor in Chile, and the South Pole are sites of large millimeter‐ or submillimeter‐wavelength telescopes. We have placed 860 GHz sky brightness monitors at all three sites and present a comparative study of the measured submillimeter brightness due to atmospheric thermal emission. We report the stability of that quantity at each site.