Ground-based optical astronomy necessarily involves sensing the light of astronomical objects along with the contributions of many natural sources ranging from the Earth’s atmosphere to cosmological light. In addition, astronomers have long contended with artificial light pollution, which further adds to the ‘background’ against which astronomical objects are seen. Understanding the brightness of the night sky is therefore fundamental to astronomy. The last comprehensive review of this subject was nearly a half-century ago, and we have learned much about both the natural and artificial night sky since. This Review considers which influences determine the total optical brightness of the night sky, the means by which this brightness is measured and how night sky quality is assessed and monitored in the long term.

地面光学天文学必然涉及感知天文物体的光以及从地球大气到宇宙光等许多自然资源的贡献。此外，天文学家长期以来一直在与人造光污染作斗争，这进一步增加了观察天文物体的“背景”。因此，了解夜空的亮度是天文学的基础。对这个主题的最后一次全面回顾是近半个世纪前，从那以后我们对自然夜空和人造夜空都有很多了解。这篇评论考虑了哪些影响决定了夜空的总光学亮度、测量这种亮度的方法以及如何长期评估和监测夜空质量。