Southern Arizona's dark skies established the region as an international hub for astronomy in the 1960s. Observatories and other sky-gazing research facilities have brought prestige — and millions of dollars — to the state.
Today, riches on the ground — or, more specifically, below it — also have the potential to enrich the state, resulting in an odd collision between mining and astronomy.
Since 2007, when Rosemont Copper, which is owned by Canada's Augusta Resource Co., announced its plans to build a mine in the desert just south of Tucson, the environmental community has warned that the project will devastate the desert landscape.
But when the mine released its draft environmental impact statement in 2009 and revealed its lighting plan for the mine, another group joined the fray: the International Dark-Sky Assn. and the numerous astronomers whose research — and livelihoods — depend on the desert's dark skies.
"The [mine's] impact on astronomy is potentially very, very significant," said Scott Kardel, public affairs director of the association, a Tucson-based nonprofit that has worked to preserve and protect the darkness of night skies since 1988.
Because the mine would operate 24 hours a day, seven days a week, nighttime floodlights required by federal safety requirements could create significant light pollution that would interfere with astronomy.
The site of the proposed Rosemont Copper Mine is 12 miles northeast of the Fred Lawrence Whipple Observatory, known for its Multiple Mirror Telescope and work in ground-based gamma-ray astronomy.
"The initial lighting estimate of the [mine's] light output was very bad," said Emilio Falco, project director at the Whipple Observatory, which is part of the Harvard-Smithsonian Center for Astrophysics.
According to that initial estimate, the mine's lumen output — the measure of the amount of visible light emitted by a source — would be 21.7 million lumens, or the equivalent of about 12,000 houses.
The scientific community and the industries that cater to the astronomers were alarmed. In 2007, a study conducted by the University of Arizona estimated that astronomy contributed $250 million annually to the state's economy.
Much of this income is generated by the jobs created by research and tourism, as well as operations-related purchases in Arizona, such as equipment, materials, or professional services.
After a period of public comment, "Rosemont saw the light, so to speak," Falco said, and hired Tucson-based outdoor lighting company Monrad Engineering, which is headed by Christian Monrad, a former president of the International Dark-Sky Assn. A new lighting plan was drafted and released in January.
If adopted, the new plan would reduce the total lumen output to a quarter of the original design — down to roughly 5.1 million lumens — by applying new lighting technologies, such as filtered light-emitting diode systems. An improved fixture design will focus light on the ground instead of spewing it into the sky.
"It's an improvement," Falco said. But even with the reduced lumen output, "the mine will still have a significant impact on the quality of the sky," he said.
With even incremental increases in sky brightness, "the faintest stars are the first to go," Falco said. "But those are the most interesting ones."
Falco worries about not only the light emitted by spotlights, but also the dust kicked up by actual mining activities. "Not just because dust will affect the performance of the telescopes," he said, "but also because dust re-directs light into the sky."
"The project as a whole will undoubtedly have some effects upon the surrounding ecosystem, as would any new development in any non-urban locale," Kathy Arnold, vice president of environmental and regulatory affairs for Rosemont Cooper, said in an email.
But, Arnold said, the new lighting plan "reduces significant amounts of the negative environmental or astronomical effects due to light at night that may have otherwise occurred" with a conventional lighting system.
The revised lighting plan hasn't swayed many environmentalists opposed to the mine. "My work is a direct expression of the beauty and integrity of this amazing landscape here," said Matilda Essig, a visual artist who has lived in the nearby town of Sonoita for the last seven years. She says many tourists who come seeking the dark skies end up in her studio buying art.
"The mine stands to have a hugely negative impact on my economic well-being," she said.
A 2009 report by Arizona State University estimated that during the projected 20-year life of the mine, it would generate $907 million annually in associated economic activity for the state and support an average of 2,900 jobs for Arizona workers.
According to an Arizona statue, mining operations like Rosemont aren't legally required to conform to county lighting ordinances. Enacted in 1972, Pima County's light pollution laws are some of the most stringent in the country, and have been successful at reining in the glow of a growing Tucson.
In 2010, a study by the Lowell Observatory measured that the sky brightness at nearby Kitt Peak has stayed "remarkably constant" over the last 20 years.
The project's fate is now in the hands of the U.S. Forest Service, which must rule on the overall mining plan, as well as what lighting would be acceptable.