On the night of February 24, 1987, a Canadian astronomer named Ian Shelton stepped outside the dome and looked up. He had been photographing the Large Magellanic Cloud and noticed a star in his plates that did not belong. Oscar Duhalde, the telescope operator on duty, had already seen it with his own eyes. They had caught Supernova 1987A, the closest exploding star observed since before the invention of the telescope, bright enough to see without any instrument at all. The place where they stood was Las Campanas, a 7-kilometer ridge of bare rock rising above the southern Atacama, where the sky is so dark and so steady that the universe seems to lean in close.
Carnegie astronomers came here in 1969 for a simple reason: the lights of Los Angeles had begun to drown out the stars above their old home at Mount Wilson. They needed darkness, and the Atacama, the driest non-polar desert on Earth, offered it in abundance. About 100 kilometers northeast of the coastal city of La Serena, the ridge sits more than 2,500 meters above sea level, above most of the weather and the dust. Nights are clear for the better part of the year, and the thin, dry air holds steady, so the stars do not shimmer and smear. For an astronomer, calm air is as precious as clear air. Las Campanas has both.
The first telescope arrived in 1971, the one-meter Swope, named for the astronomer Henrietta Swope. The larger 2.5-meter Irénée du Pont followed in 1977. Then came the giants. The two Magellan telescopes, each carrying a single 6.5-meter mirror, are near-identical twins: the Walter Baade saw first light in 2000, the Landon Clay in 2002. They are run by an international consortium of universities and institutions. It was the one-meter Swope Telescope here that, in 2017, first captured the visible-light glow of two neutron stars colliding, the first time anyone had seen the optical counterpart of a gravitational wave. The ridge has become one of the most productive patches of ground in modern astronomy.
Near the southern end of the ridge, on a peak called Cerro Las Campanas, construction is underway on something larger still. The Giant Magellan Telescope will gather light with seven enormous mirrors, each 8.4 meters across, arranged like the petals of a flower around a central one. Together they form an effective aperture of 25.4 meters and a light-collecting surface of 368 square meters, roughly fifteen times the area of a single Magellan mirror. The first mirror was cast back in 2005 at the University of Arizona's Steward Observatory Mirror Lab, where the glass is spun in a rotating furnace until it settles into a perfect curve. When commissioning begins, expected in the early 2030s, the telescope should see fainter and sharper than almost anything before it.
What draws astronomers to a mountaintop like this is the chance to catch light that left its source billions of years ago, light so dim that a single stray glow on the horizon can erase it. From here, researchers hunt for planets around other stars, weigh the dark matter that holds galaxies together, and trace the expansion of the cosmos itself. The work is patient and unglamorous, long nights in cold domes, but the payoff can be sudden, as it was for Shelton and Duhalde. Somewhere in the data streaming off this ridge tonight may be the next discovery nobody expected.
Las Campanas Observatory sits at 29.02 degrees south, 70.69 degrees west, on a ridge rising above 2,500 meters at the southern edge of the Atacama Desert in Chile's Atacama and Coquimbo regions. From the air the white telescope domes stand out against the bare ochre ridgeline, with the Pacific coast roughly 100 km to the southwest. The nearest airport is La Serena's La Florida Airport (ICAO SCSE), about 100 km to the southwest. Recommended viewing altitude is 9,000 to 12,000 feet for the surrounding desert ranges; the air here is famously clear and stable, with visibility often exceeding 100 km on calm days.