Atmospheric extinction and night-sky brightness at Mauna-Kea.

We present a summary of atmospheric extinction values obtained at the 4200-m and 2800-m elevations of Mauna Kea over the years 1980 to 1986. The wavelengths of the 17 filters in question range from 0.44 μm to 32 μm. While it is possible to obtain an accurate mean extinction value at a given wavelength, there is considerable scatter about the mean for all infrared wavelengths. At visual wavelengths the extinction at the Mauna Kea summit exhibits much less variance. At the summit we find median extinction values of B = 0.19, V = 0.11, J = 0.10, H = 0.05, and K = 0.07 mag/air mass, respectively. At the 2800-m level we find a median V band extinction of 0.18, and mean reddening k_bv = 0.125 ± 0.020 for a star with (B -V) = 0.0. During 1986 the night-sky brightness at the 2800-m level was measured to be V = 21.5, B = 22.3 mag sec^-2.