The History of Las Campanas Observatory

Graced with clear, dark skies and an exceedingly arid climate, Chile's Atacama Desert boasts astronomical "seeing" that is the best in the world. It has become a mecca for stargazers with more than 20 observatories dotting its austere landscape. Over 50 years ago, Carnegie astronomers chose to build an observatory in the Atacama—the institution's Las Campanas Observatory—which would become the cornerstone of Carnegie Science's modern astronomical research program.

A Century-Old Vision

The idea for Carnegie Science to build a southern observatory is almost as old as the institution itself. In 1902, the Advisory Committee on Astronomy set forth a bold argument for a southern viewing station. Their report, published in the institution’s first year book, noted that Northern Hemisphere observatories outnumbered southern facilities by 10 to one, creating what they termed a "great deficiency" that "ought to be remedied." The skies of the Southern Hemisphere, home to the Galactic Center, the Magellanic Clouds, and countless celestial objects invisible from northern latitudes, were astronomically neglected. The committee's remarkably foresighted recommendation for a southern hemisphere observatory acknowledged that such an ambitious project "may not be realized in full for many years to come." In fact, it would take more than six decades to fulfill their vision.

In the intervening years, Carnegie established itself as a giant in astronomy. The institution's Mount Wilson Observatory, founded in 1904 in the mountains above Pasadena, became home to the world's largest telescope. Here, Edwin Hubble would discover the universe and the fact that it is expanding, fundamentally changing our understanding of the cosmos. Later, Carnegie's partnership with Caltech brought the mighty 200-inch Hale telescope to life at Palomar Observatory, further cementing the institution's reputation as a pioneer in building the world's most powerful astronomical instruments.

Yet the southern skies remained out of reach. Legendary Carnegie astronomers like George Ellery Hale, the visionary behind Mount Wilson, and his successor, Walter Adams, periodically revived calls for a southern observatory, but practical challenges and competing priorities prevented the realization of such a project. As the 1960s dawned, there was still no place for Carnegie’s astronomers to view the southern skies, no place for them to see the center of the Milky Way or the Magellanic Clouds.

The Push for Southern Skies

In 1962, Carnegie astronomers Ira Bowen, Horace Babcock, and Robert Leighton developed a long-term plan for the institution's astronomical facilities that elevated the southern observatory project from aspiration to priority. Their effort was well-timed. The landscape of international astronomy was changing, and both the Associated Universities for Research in Astronomy (AURA) and the European Southern Observatory (ESO) had recently initiated their own plans for new observatories in the southern hemisphere. In a letter to then-Carnegie President Caryl P. Haskins, Bowen emphasized the competitive necessity of establishing a major southern telescope to maintain the institution's leadership in astronomy.

The decision came down to embracing George Ellery Hale's famous exhortation: "Make no small plans." The astronomers gained support from Carnegie’s leadership and Trustees, who at a special committee meeting in May 1963 urged that high and early priority be given to developing an observatory in the Southern Hemisphere. Later that month, the trustees approved funds for a comprehensive site survey, officially launching the Carnegie Southern Observatory (CARSO) project.

The Search for the Perfect Site

The responsibility for site selection fell to Horace Babcock, who was appointed director of the Mount Wilson and Palomar Observatories in 1964. Babcock was well-suited to the challenge and would go on to play a large role in the creation and early years of Carnegie’s southern observatory. A distinguished astronomer at the peak of his career, with a bent for engineering matters, Babcock would prove himself skilled at dealing with scientists and technicians, the institution’s leadership and trustees, and Chilean officials alike.

In late 1963, Babcock arrived in Santiago for the first site trip, where he set off aboard Chilean army transport for La Serena, a coastal town about 250 miles to the north. His ultimate destination was the barren region inland of La Serena, where dry, stable air and high elevation—which would reduce the atmosphere’s distortion of incoming light—create the perfect conditions for astronomical observation of the sky’s southernmost celestial objects. 

Astronomical Seeing Monitors (ASM) were flown in from California for the evaluation process. These instruments, consisting of an 8-inch self-guiding telescope and an electronic recording device, measured the steadiness in position of a star as seen through the Earth’s atmosphere and were used to quantify the astronomical “seeing” of potential sites.

While Chile emerged early as the preferred location, scientific rigor demanded comprehensive evaluation of alternatives. With an ASM in tow, Babcock set off in April 1964 for site visits to New Zealand, which proved too cloudy, and Australia, which was more promising. However, accumulated data soon demonstrated Chile's superior “seeing” for astronomical observation.

Astronomer John B. Irwin, arrived in Chile in June 1964, charged with establishing a permanent presence for onsite testing that he would continue for three years. Initial collaboration with AURA appeared promising, with the consortium offering to sell Carnegie a tract near their Cerro Tololo site and providing access to site test at Cerro Morado, a promising peak within their holdings.

Las Campanas: The Chosen Peak

However, a pivotal development occurred in July 1966 when Irwin drove north from Cerro Morado to scout a promising ridge marked on his map as "Campanita." His initial reconnaissance, followed by a September summit expedition to climb to the top of the 8,000-foot peak, revealed promising characteristics, including level ground and potential water sources. He concluded that the site “looks like a real possibility.”

On Babcock’s next visit to Chile in October 1966, he and Irwin made the 5.5-hour round trip trek to the top of the peak, now correctly identified as Las Campanas— “the bells,” likely named for the unique ringing sound certain rocks at the peak make when they are struck. (The true Campanita, “little bell,” is a lower peak situated two miles to the west.) Standing on that remote mountaintop, Babcock recognized the promise of the site. Its remoteness guaranteed dark skies free from light pollution, while its position at the southern end of the Atacama Desert promised the driest, clearest air on Earth.

Over the following two years, Las Campanas evolved from a promising site to Carnegie's preferred location. By November 1968, after another visit to Las Campanas, Babcock made up his mind to recommend that Carnegie make a final decision to build its southern observatory at Las Campanas. 

Stopping in Santiago on his return journey, Babcock was surprised to learn that earlier efforts to meet with the Chilean president had borne fruit, and he was scheduled to speak with President Eduardo Frei the following morning. That November 19 meeting would prove decisive for the project’s future. Babcock described Carnegie’s five-year testing efforts to a receptive Frei and mentioned that the institution might seek property rights for land around Las Campanas, which was at that time owned by the Chilean government. 

According to a retelling of the events, “To Babcock’s surprise, Frei picked up the telephone and said to his Minister of Land that he wanted an agreement to be rapidly completed to Carnegie’s desires. Putting down the telephone, Frei told Babcock that ‘the land is yours. You can telephone to the United States to start construction of the telescope immediately.’”  

Things had moved unexpectedly quickly—Babcock hadn’t even had prior authority to commit the institution to this direction at the time—but Carnegie seized the remarkable opportunity. Negotiations proceeded smoothly, and the purchase of 50,000 acres at Las Campanas was completed in July 1969. Las Campanas Observatory was born.

From Barren Mountaintop to World-Class Observatory

The transformation of the barren mountaintop into a world-class observatory was soon underway. Babcock signed a new cooperative agreement with the University of Chile under the auspices of the Chilean Ministry of Foreign Affairs for entry of Carnegie staff and equipment and for future cooperation in using the telescopes. The institution purchased a plot of land in La Serena known as El Pino as a site for a future administrative office. At Las Campanas a 20-mile access road was carved through the desert, a reliable water supply was developed, and buildings rose from the rocky ground.

By 1971, Carnegie's first telescope at Las Campanas was ready for dedication. The 1-meter (40-inch) Swope telescope, named for astronomer Henrietta Swope, whose generous 1967 gift was used for site development and the purchase of the telescope, saw first light the following year.

Even before the Swope telescope was finished, construction of a second telescope had begun, this one designed entirely by Carnegie astronomers. The 2.5-meter (100-inch) Irénée du Pont telescope, built with a $1.5 million donation from Carnegie trustee Crawford Greenewalt and his wife, Margaretta, was dedicated in 1976 with first light the following year. (Greenewalt was, at the time of his donation, chairman of the du Pont board. The telescope was named after Margaretta’s father.)

Babcock had originally planned to build a 5-meter telescope at Las Campanas to rival the Hale instrument at Palomar. But when the Ford Foundation turned down his application, funding became an issue. The Greenewalt donation enabled the institution to go forward, though on a smaller scale.

By the late 1970s, with more resources flowing to Las Campanas, Carnegie decided it was time to end its long-term relationship with Caltech. In 1979, the two institutions severed their formal agreement, and the Mount Wilson and Palomar Observatories became the Mount Wilson and Las Campanas Observatories. In 1986, the institution relinquished management of its historic telescopes on Mount Wilson, which were no longer equipped to conduct deep-sky observing due to light pollution from the nearby metropolis. This marked the transition of Carnegie's astronomy program from its California roots to its new focus on the pristine skies of Chile.

The Magellan Project

With Carnegie fully committed to its southern site, the 1990s brought Las Campanas Observatory’s most ambitious project yet: the Magellan telescopes. These twin 6.5-meter giants, constructed on Cerro Manqui about 100 meters higher than the du Pont telescope, represented the cutting edge of telescope technology. 

The Magellan project embodied a new model of astronomical collaboration, bringing together scientists from Harvard University, MIT, and the Universities of Arizona and Michigan. The Walter Baade Telescope (named after the former Carnegie astronomer) and the Landon Clay Telescope (named after a businessman and philanthropist) saw first light in 2000 and 2002 respectively. 

The Magellan telescopes are widely considered among the best natural imaging telescopes in the world and have contributed to groundbreaking discoveries in exoplanet research and galaxy formation and evolution, cementing Las Campanas' reputation as a premier site for cutting-edge astronomical research.

A Living Legacy 

In the years since its founding, the Las Campanas Observatory developed into one of the premier astronomical observing sites in the world. Today, Carnegie astronomers, along with their colleagues around the world, keep the telescopes in operation nearly every night of the year, taking advantage of the Atacama Desert's extraordinary atmospheric conditions. 

The observatory continues to evolve with advancing astronomical technology. In 2023, the Local Volume Mapper was constructed at Las Campanas Observatory as part of the Sloan Digital Sky Survey's fifth generation, enabling new research on the cosmic ecosystem surrounding the Milky Way galaxy. The facility consists of four custom-built telescopes that capture visible light from the night sky with unprecedented speed, channeling it through 2,000 optical fibers to a suite of three spectrographs for detailed analysis.

But Las Campanas’s greatest chapter may still lie ahead. The Giant Magellan Telescope, now under construction at Las Campanas Observatory, will dwarf all previous instruments with its revolutionary design incorporating seven 8.4-meter mirrors working as one. When completed, this next-generation telescope is poised to transform the field of astronomy. From unveiling the intricate details of distant exoplanets to shedding light on the elusive nature of dark matter, the Giant Magellan Telescope promises a treasure trove of discoveries. As the Giant Magellan Telescope takes shape on the desert mountaintop, it carries forward the same spirit of discovery that drove Carnegie's astronomers to venture into the Chilean desert more than half a century ago.