The Greater Big Bend International Dark Sky Reserve

The rapid spread of light pollution threatens ground-based observatories even in remote locations. To help combat this threat, the University of Texas at Austin’s McDonald Observatory, The Nature Conservancy, the International Dark-Sky Association (IDA), and many others partnered to create the Greater Big Bend International Dark Sky Reserve. With an area of over 38,000 square kilometers in Texas and Mexico, the Reserve became the largest IDA-recognized dark sky place in the world when it was certified in April of 2022. The Reserve is only the second dark sky place in the world to cross an international border. It is composed of a core area that protects the McDonald Observatory and The Nature Conservancy’s Davis Mountains Preserve, surrounded by a large peripheral area that supports the core and serves as a buffer. The creation of the Reserve is the result of decades of efforts in the region to educate the public about the impacts of light pollution and promote better lighting practices. Thirteen counties and municipalities updated their outdoor lighting ordinances to support the Reserve effort. A large-scale sky quality monitoring campaign using handheld sky quality meters, all-sky photometry methods, and remote sensing was necessary to measure light pollution and obtain certification. A campaign to address light pollution from oil and gas industry activity has resulted in several operators adopting the McDonald Observatory’s recommended lighting practices, contributing to an estimated twenty percent overall reduction in light pollution between 2019 and 2022. The success of the Reserve’s strategy offers a model for other ground-based observatories to reduce light pollution in their own regions.