Optical Night-Sky Brightness at Mauna Kea over the Course of a Complete Sunspot Cycle

We have produced a data base of V-band and B-band night-sky brightness measurements rather evenly spread out over the course of a whole sunspot cycle from September 1985 to August 1996. Almost all the data were obtained at the 2800-m level of Mauna Kea using the same telescope, same photomultiplier tube, filters, and diaphragm, thus minimizing various sources of systematic error and allowing an estimate of the sources of random error. The yearly V-band averages of observed sky brightness ranged from 21.287 to 21.906 magnitudes per square arc second. The color of the sky is $B-V$ = 0.930 and does not change discernibly over the course of the sunspot cycle. After correcting the V-band data to the zenith, we find that the airglow component varied a factor of 4.5 over the course of the solar cycle. Once the 11-year solar cycle effect is removed from the data, the most significant contribution to the scatter of individual data points appears to be the short term variations on time scales of tens of minutes like those observed by the Whole Earth Telescope project.

K. Krisciunas · 1997