The Mt. Wilson Observatory in the Angeles National Forest may look remote, but urban sprawl from Los Angeles means that it is much closer to dense human activity today than it was when it was established in 1904. (USDA/USFS (CC BY 4.0))
When the Mt. Wilson Observatory was constructed in the Angeles National Forest near Pasadena, California, in the early 1900s, it was a very dark site, considerably far from the 500,000 people living in Greater Los Angeles. Today, 18.6 million people live in the LA area, and urban sprawl has brought civilization much closer to Mt. Wilson.
When Kitt Peak National Observatory was first under construction in the late 1950s, it was far from metro Tucson, Arizona, with its population of 230,000. Today, that area houses 1 million people, and Kitt Peak faces much more light pollution.
Even telescopes in darker, more secluded regions – like northern Chile or western Texas – experience light pollution from industrial activities like open-pit mining or oil and gas facilities.
European Southern Observatory’s Very Large Telescope at the Paranal site in the sparsely populated Atacama Desert in northern Chile. (J.L. Dauvergne & G. Hüdepohl/ESO (CC BY-ND 4.0))
The case of the European Southern Observatory
An interesting modern challenge is facing the European Southern Observatory, which operates four of the world’s largest optical telescopes. Their site in northern Chile is very remote, and it is nominally covered by strict national regulations protecting the dark sky.
AES Chile, an energy provider with strong U.S. investor backing, announced a plan in December 2024 for the development of a large industrial plant and transport hub close to the observatory. The plant would produce liquid hydrogen and ammonia for green energy.
Even though formally compliant with the national lighting norm, the fully built operation could scatter enough artificial light into the night sky to turn the current observatory’s pristine darkness into a state similar to some of the legacy observatories now near large urban areas.