• Skies would be 22 percent brighter at a 20-degree angle above the horizon near Levy's Jarnac Observatory, five miles north of the mine site. The 20 degrees represent the lowest useful area of the sky for astronomical observations.
• Skies would brighten 10 percent at 20 degrees at the Whipple Observatory on Mount Hopkins, 10 miles west of the mine.
• At the Empire Ranch, east of Arizona 83 and a few miles south of the mine, brightness would rise 32 percent. The Tucson Amateur Astronomy Association held monthly stargazing parties there until about eight months ago, and individual members still go there occasionally.
