Measurements of sky brightness at Bosscha Observatory, Indonesia

To determine the level of light pollution due to human activities, we performed sky-brightness measurements at Bosscha Observatory, Indonesia (107°36'E; 6°49'S, 1300 m above sea level) for seven years from 2011 to 2018, using a portable photometer pointed at the zenith. From 1692 nightly records, we found that the average brightness on moonless nights reached the 19.70 ± 0.84 and 19.01 ± 0.88 astronomical magnitudes per square arcsecond (mpass), with median values of 19.73 mpass and 19.03 mpass for the AM and PM periods, respectively. The darkest skies occurred in the peak of the summer season during the month of July, which corresponds to the lowest annual temperature, precipitation, and relative humidity. The internal temperature of our Sky Quality Meter is adequately stable, and our results correlate well with other measurements. The sky brightness depends on the age of the Moon (days past new Moon) and on seasonal monthly variations, but it is not related to the lunar distance. The night-SB quality can be modified by the coupled climate system as a diurnal cycle to an 11-year solar cycle. The cities around the Observatory, Bandung and Lembang, clearly make strong contributions to light pollution in the area due to unshielded light sources.