People watch a solar eclipse at La Silla Observatory in La Higuera, Chile, on July 2. (Martin Bernetti/AFP/Getty Images)

It’s extremely rare to have a complete solar eclipse pass over an observatory. On Tuesday, it happened over two. The observatories in Chile’s Atacama Desert, the darkest, driest part of the world, are less than 70 miles apart ⁠ — one funded by the National Science Foundation (NSF) and the other by 16 European countries.

The two groups celebrated the phenomena in very different ways: One used it for a research push; the other, a party.

“It’s only the third time this has happened in history,” said Lars Lindberg Christensen, head of outreach and initiatives for the European Southern Observatory (ESO). “After the totality, there will be a toast. We’re super excited to have so many people here."

At ESO’s La Silla Observatory, which sits at almost a mile and a half in altitude, Christensen and his colleagues hosted 150 VIPs, including Chilean President Sebastián Piñera, business magnate Bill Gates and numerous ambassadors. About 1,000 members of the public attended, along with English rock star Steve Rothery, who performed a concert.

This artist's rendering shows how the total solar eclipse appeared from ESO's La Silla Observatory. (M. Druckmüller, P. Aniol, K. Delcourte, P. Horálek, L. Calçada/ESO)

Conditions were perfect for sky gazing. A few hours before the moment when the moon comes between the earth and sun, and casts the darkest part of its shadow on Earth, a dark blue strip of ocean was visible from the Europeans’ perch. A strong Antarctic Ocean chill, the Humboldt current, was creating a cloud inversion, which pulls all fog low to the coastline. This clear-sky weather of the desert mountain range, squished remarkably close to the coastline, is why the area became a go-to site for multiple giant telescopes starting in the 1960s.

With viewing conditions optimal, the Europeans gave their VIP guests a close-up perspective of solar research. Ambassadors and others watched as ESO’s scientists pulled back the dome and used the massive New Technology Telescope to measure atoms of the sun’s corona, which appears as the wispy crown of light around the black disk of an eclipsing moon. The physics of this crown, actually the outermost part of the sun’s atmosphere, “is still a little bit of a mystery,” Christensen said. It is best measured during the rare times when the moon visibly passes over the sun. For the Atacama desert, this last occurred over a century ago.

The astronomers moved the massive telescope under enormous time pressure. They had under a minute to make measurements when the surface of the sun is blocked. This is the time when ambient light became noticeably darker — likely darker than what Americans experienced during 2017′s “Great American Solar Eclipse” because of all the man-made light in large swaths of the United States.

After the light returned, the VIPs sipped cocktails next to scientists, soaking in celestial awe. The tours, concert and global camaraderie followed. The Chilean news outlet La Tercera reported that Facebook co-founder Mark Zuckerberg and Virgin Galactic founder Richard Branson were among those in attendance.

Across the desert, the American observatory was closed to the public, mostly because of safety concerns. “There’s not a lot of space . . . we’re mostly focusing on the science,” says Shari Lifson, communication coordinator at the Association of Universities for Research in Astronomy (AURA). Just one very steep, dirt road goes to the NSF observatory. It can be extremely windy.

Instead of having a public party, the Americans invited five teams of visiting scientists to perform experiments.

“We’ve been here for almost a week preparing out on top of this mountain, with no chance to get off,” said Paul Bryans, who led one of the three research teams based at the American facility, Cerro Tololo Inter-American Observatory. He’s trying to better predict space weather with compact, low-tech instruments that he and his team experimented with during the eclipse.

He described the facilities as clean but spartan. No alcohol allowed. When asked about the party happening just across the desert, Bryans chuckled. “I don’t know if that will be so good for observing. Real astronomers work.”

Not all of the American scientists were based at the NSF observatory. Jay Pasachoff of Williams College worked at an isolated site 62 miles north of the observatory. Shadia Habbal of the University of Hawaii was studying the sun’s corona from three different locations across South America.

The Americans also hosted a live feed of the solar eclipse for people who lived outside Chile and Argentina, the only counties where it was visible. That feed was projected on a giant screen in the Embassy of Chile in Washington. Many NSF staffers were in attendance at a small watch party.

Richard Green, NSF division director for astronomical science, made a point to inform the group of the U.S. government’s long-standing commitment to Chile-based astronomical observations. “Altogether, the U.S. has made a billion-dollar capital investment,” in the region’s space science activities, he said, including older telescopes, like Cerro Tololo, built in the 1960s, and newer NSF-funded telescopes that will start operating in 2021.

“I do think Americans are in fact celebrating and supporting space observation,” said Camila Garcia, attache for science and technology at the Embassy of Chile. But she suggested the Europeans take a wider view, hosting VIP parties to explore the potential of philanthropic donors to help fund new instruments.

Increasing society’s capacity to ask important questions was a central goal of the European observatory public program Tuesday. “The science needs to be bigger,” Christensen said. “The telescopes need to be bigger.”