When the late Pope Francis was elected, a dozen years ago, and famously declined the pomp and perquisites typically associated with the office, among his renunciations was the use of the papal summer residence—a seventeenth-century palazzo in Castel Gandolfo, about fifteen miles south of Rome. Generations of Popes had enjoyed the use of the mansion, which overlooks a volcanic lake and is surrounded by spectacular terraced gardens. The palazzo is now a museum where visitors can admire a gallery of papal portraits, of varying quality, and imagine the dreams that visited the successive occupants of the papal bedroom, with its narrow twin bed. Castel Gandolfo is also home to one of the Holy See’s more unexpected institutions: the Vatican Observatory, which since its founding, in 1891, has been dedicated to the scientific study of the heavens.

Guy Consolmagno, the director of the observatory, first came to Castel Gandolfo as a newly minted Jesuit brother, in 1993. When I met him outside the palazzo, early this spring, he gestured at a window overlooking the building’s courtyard. This was the location of his first, decidedly modest bedroom in the mansion. Consolmagno, who grew up in suburban Detroit and retains a buoyant, emphatic, Midwestern manner, told me, “The Pope then was John Paul II, and when he was first elected he had made a rookie mistake, as we say in America. Somebody, a journalist—one of those terrible journalists—had asked him, ‘What’s your favorite hymn?’ And, being a fool, he actually gave the name of a hymn that he happened to like. So, every Sunday during the summertime, when he was living here, the doors would open at 10 a.m., and this place would be filled with two thousand Polish pilgrims singing that hymn underneath my window. I got totally sick of it.” Consolmagno never got sick, though, of being saluted by the Swiss Guards stationed at the palace gates.

Consolmagno, who has a prodigious white beard, wavy gray bangs, and dark, beetling eyebrows, is one of fifteen scientists who currently make up the scholarly staff of the Vatican Observatory—all Jesuits and, inevitably, all men. (Their meals, perhaps equally inevitably, are prepared by a local woman.) At any given moment, about half of the fraternity is in Castel Gandolfo, which has been the institution’s home since the nineteen-thirties—although, for the past fifteen-odd years, the staff’s living quarters have been situated in a former convent a short distance from the palace. The other half of the team is in Arizona, a state that offers a remote mountain environment more conducive to astronomical observation than the light-polluted suburbs of Rome do. In the early nineties, at the Mt. Graham International Observatory, near Tucson, the Vatican installed a powerful four-million-dollar telescope and an astrophysics facility, together known as the Vatican Advanced Technology Telescope, or VATT. Consolmagno, like many of his colleagues, shuttles frequently between Italy and Arizona, rarely spending more than a few months in one place.

Consolmagno likes to say that, when he arrived in Castel Gandolfo, the director at the time, Father George V. Coyne, told him that he had only one job: to do good science. At first, Consolmagno was engaged mostly with taking painstaking measurements of specimens from one of the world’s preëminent collections of meteorites, which was bequeathed to the institution, in the early twentieth century, by a French nobleman, the Marquis de Mauroy. Consolmagno and several colleagues developed a new method for measuring the density and porosity of meteorites. The approach is not a million miles from the revelation delivered to Archimedes as he displaced water in his bath: the specimens are submerged in a vessel filled with helium gas, the molecules of which are small enough to penetrate tiny nooks and crannies in the rocks; if the specimens are then submerged in a vessel filled with glass beads that are tiny but too large to penetrate such spaces, the difference between the two volumes helps reveal the rock’s porosity. Sara Russell, a planetary scientist at the Natural History Museum in London—and a friend of Consolmagno’s since the mid-nineties, when they met on a meteorite-hunting expedition in Antarctica—told me, “He started out making simple measurements, and over the years his method got more and more sophisticated, and managed to make fundamentally important observations.” Among other contributions, the Vatican Observatory has made available to scientific researchers fragments of a rare meteorite, known as Chassigny, whose chemical composition suggests that it originated in the mantle of Mars.

Like research institutions that are not staffed with those who have taken religious vows, the Vatican Observatory collaborates with scientific colleagues around the globe. These have included, in recent years, NASA, whose OSIRIS-REx mission (2016-23) collected samples from the Bennu asteroid, which measures a third of a mile across and has been calculated to have a not infinitesimal chance of colliding with Earth in the twenty-second century. Bob Macke, another Jesuit brother in Castel Gandolfo, has developed a specialty in documenting the properties of meteorites, and several years ago he was invited to join an international team analyzing the Bennu samples; in 2023, he built a device specifically adapted for carrying out these delicate measurements. “NASA needed help with a mission. The Vatican came to the rescue,” read one headline about the collaboration.

Although the Vatican Observatory produces a wealth of peer-reviewed science, its structure is much different than, say, an astronomy department at a university. The Arizona telescope’s daily operations are funded by private donors to a not-for-profit foundation, and the Jesuit staff’s administrative costs and salaries are covered by the Holy See. Scientists at the observatory are liberated from the secular scholar’s pursuit of tenure, grant money, and commercial investment; moreover, the Jesuits, having taken a vow of poverty, have extremely low living costs. Like the builders of a fourteenth-century cathedral, they are able to take the long view. In Castel Gandolfo, Consolmagno explained that, nearly two thousand years ago, the site had been the location of a palace belonging to the Emperor Domitian. (Some fragmentary ruins remain on the castle grounds.) Christians were exiled under his rule, “and now his gardens belong to the Pope,” Consolmagno said as we walked beneath cypresses and umbrella pines, with evident satisfaction at the comeuppance.

As director, a post he has held for the past decade, Consolmagno spends far less time peering through a telescope or a microscope than he once did, and far more time explaining to the public why doing those things is not incompatible with religious conviction. He is constantly on the road, all over the world, giving talks to religious and secular audiences alike, often billed as “the Pope’s Astronomer.” At these events, he fields such questions as whether there is any recorded evidence for an actual Star of Bethlehem. (There is nothing conclusive, but scientists have identified various suggestive celestial phenomena in the years around the birth of Christ, including alignments of planets which might, to the naked eye, look like bright stars.) Consolmagno is also well known in the science-fiction community, of which he became a devout member as a young adult. He still shows up at sci-fi conventions whenever he can. His preferred subgenre is the space opera, with its dramatic adventures and heroic plots; he confesses to reading such works on his phone before bed, in violation of sleep-hygiene strictures. Patrick Nielsen Hayden, an editor at Tor Books, which publishes science fiction, and a friend of Consolmagno’s from the scene, told me, “He’s, like, the least proselytizing dude you could possibly imagine, given that he’s a Jesuit brother and it permeates his whole identity.” Nielsen Hayden, who characterizes himself as a “grumpy, reluctant, argumentative Catholic,” added that Consolmagno “has a tremendous capacity for affable friendship and civilized exchange with people from belief structures completely different from his own.” Consolmagno has written numerous popular-science books for general audiences, ranging from a plainspoken credo, “Finding God in the Universe,” to the puckishly titled “Would You Baptize an Extraterrestrial? . . . and Other Questions from the Astronomers’ In-Box at the Vatican Observatory,” which he wrote with Father Paul Mueller. (The short answer to the extraterrestrial question: only if the alien asked him to.)

Brother Guy, as he is widely known, never suggests that science might offer a means to prove the existence of God, or even to indicate a high probability of His existence. Consolmagno does not subscribe to what is known as the anthropic principle, which argues that the physical properties of the universe are so fine-tuned within the extraordinarily narrow range allowing for the emergence of intelligent life that the cosmos must have been made for us. Nor is he tempted by concordism—the idea that the discoveries of modern science can prove that events described in the Bible are grounded in reality. “Scripture was not written to tell you about the natural world,” Consolmagno told me. “It was to tell you about God.” The most egregious example of concordism, he said, was offered by Pope Pius XII, who had studied science and was interested in astronomy; in 1951, Pius XII gave a speech to the Pontifical Academy of Sciences in which he characterized the big bang as confirming the Book of Genesis by “bearing witness to the august instant of the Fiat Lux, when, along with matter, there burst forth from nothing a sea of light and radiation.” Pius XII stopped suggesting that the big bang required the orchestration of God after he had a conference with Georges Lemaître, the Belgian scientist and Catholic priest who had laid the groundwork for the theory with his hypothesis that the universe had expanded from a “primeval atom.”

Pope Francis, under whose papal reign Consolmagno was appointed head of the Vatican Observatory, was a Jesuit, the first member of that order ever elected to the papacy. Although Francis did not have a particular interest in astronomy, he believed that scientific inquiry and the mission of the Church could meaningfully intersect: among his most significant statements was the encyclical “Laudato Si’,” which urged action against global warming and environmental degradation. Consolmagno approved of this intervention, and also admired Francis’s humility and spirit of intellectual openness. Unlike Lemaître, Consolmagno and his colleagues do not advise the Vatican on celestial matters; they are left to get on with their work, and have nothing to do with doctrine. Consolmagno rarely goes to the Vatican proper; he’s too busy elsewhere. When I visited him in Castel Gandolfo, he told me it had probably been a decade since he had been inside St. Peter’s Basilica.

Consolmagno believes in the big bang, at least as a provisional explanation of the universe’s origins, and also in a creator God who exists before and beyond the big bang. In his understanding, the spheres of science and religion do not entirely overlap. Rather, they “live together—the one doesn’t replace the other,” he told me. “Using science to prove religion would make science greater than religion. It would make your version of God subservient to your understanding of the universe. And not only does that make for a pretty weak God, but it is also crazy, because in a thousand years’ time the scientific questions that people ask are going to be very different. Science goes obsolete—it doesn’t progress otherwise.”

Among the research projects to which the telescope in Arizona has contributed is a fifteen-year analysis of objects in the Kuiper Belt, a band of ice-rich asteroids in the distant solar system. Many of the objects have been found to have curious orbits that, according to some scientists, suggest they are under the gravitational sway of a massive planet—as yet undiscovered—beyond Pluto. Other colleagues have used the VATT to observe near-Earth asteroids that may offer the possibility of commercial exploitation. Consolmagno characterizes the Vatican Observatory as deliberately doing middle-of-the-road science and practicing middle-of-the-road religion. “If people think you have to be a weird kind of scientist to be religious, or a weird kind of religious to be a scientist, then we’ve missed the point,” he said. “The point is that our faith—our ordinary faith—fits perfectly with our ordinary, but wonderful, delightful science.” Some years ago, the International Astronomical Union named an asteroid in honor of his contributions to science. Somewhere between Mars and Jupiter, the asteroid 4597 Consolmagno continues its celestial course.

The Church’s study of the stars dates back at least as far as the late sixteenth century. Under the leadership of Pope Gregory XIII, a meridian line was installed in the Vatican to illustrate the need to reform the Julian calendar. A Jesuit, Christopher Clavius, helped propose that the Vatican adopt the Gregorian calendar, which it did in 1582. According to the historian Jonathan Wright’s book “The Jesuits,” when the realignment caused ten days to be subtracted from the year, mobs across Europe attacked Jesuit houses to protest the time stolen from them.

In the late eighteenth and early nineteenth centuries, an observatory was built atop the Vatican Library and Museum, in what is known as the Tower of the Winds. Eclipses were observed and meteorological measurements were taken. The Vatican Observatory that exists today was set in motion by Pope Leo XIII when, in the late nineteenth century, he devoted a second observation tower in the Vatican to astronomical work. Fortuitously, this occurred around the time that an international community of astronomers, at a gathering in Paris, decided to embark on a collaborative project to make the first photographic map of the sky. Responsibility for charting different zones of the heavens was assigned to different national observatories; the Vatican was granted its own share of the sky to map, and was thus able not only to participate in cutting-edge science but also to assert its identity as a sovereign nation, despite being less than a fifth of a square mile. By the thirties, however, light pollution had made the center of Rome inhospitable to the observatory, and the Pope—now Pius XI—offered the use of Castel Gandolfo as a future base of operations. Two new telescopes were built there, and the running of the observatory was formally taken over by the Society of Jesus, better known as the Jesuits, the Church’s most intellectually powerful division.

During the Second World War, the papal property in Castel Gandolfo was neutral territory; two thousand people displaced from local villages flooded into the palazzo’s gates to seek shelter, sleeping in a grand hall previously used for papal audiences or dwelling in a shantytown on the castle grounds. In subsequent years, research once again flourished, with the construction of another new telescope in the papal gardens. It was through this device that the Pope—now Pope Paul VI—peered at the moon on the night of July 20, 1969, when Apollo 11 made its historic landing. Afterward, he addressed the astronauts: “Honor, greetings, and blessings to you, conquerors of the Moon, pale lamp of our night and our dreams! Bring to her, with your living presence, the voice of the spirit, a hymn to God, our Creator and our Father.”