By David Willey
BBC News, Rome
For the second time in seven years the Vatican is hosting a scientific conference for astronomers.
Conference delegates will grapple with concepts of space and time
More than 200 scientists from 26 countries including the United States, Britain, Italy, Germany, Russia, and Japan have gathered in Rome for a five-day meeting on disc galaxies.
At the Papal University in Rome, normally frequented by Catholic theologians studying the Bible, the scientists, including Jesuit priests who work at the Vatican's own astronomical observatory, will be grappling with abstruse formulae and mathematical simulations about the physical origins of the universe, involving concepts such as cold dark matter and black holes.
Father Jose Funes, the head of the Vatican Observatory, said exciting new discoveries have been made with the help of space telescopes since the Holy See's last meeting on galaxies in 2000.
"Disc galaxies are a hot topic," he said.
Father Funes has a small full-time staff of only 13 scientists, most of them Jesuit priests, to run his astronomical research programmes, but co-operates with many prestigious universities around the world.
Why does the Vatican fund astronomical research after centuries of public dispute over the relative roles of science and religion?
Jesuit Brother Guy Consolmagno, a member of Father Funes's team and curator of one of the world's most important collections of meteorites, kept at Castelgandolfo (the Pope's summer residence), explains.
"They want the world to know that the Church isn't afraid of science," he said.
"This is our way of seeing how God created the universe and they want to make as strong a statement as possible that truth doesn't contradict truth; that if you have faith, then you're never going to be afraid of what science is going to come up with.
"Because it's true."
The conference kicked off with a discussion about our own galaxy, the Milky Way, before proceeding to more abstruse concepts of space and time involving how galaxies, stars and planets came to be formed and evolve.
The Catholic Church became seriously interested in stargazing as far back as four centuries ago, when Pope Gregory XIII set up a committee to examine the implications for science involved in the Pope's 1582 reform of the calendar.
In that year the Julian calendar, used since the days of Julius Caesar, was replaced by the more scientifically accurate Gregorian calendar.
Galileo was persecuted by the Catholic Establishment
The Julian calendar year had been calculated slightly too long, and after the passage of many centuries the spring equinox had drifted backwards, causing errors only remediable by a shift to a new calendar system.
Then came Galileo Galilei, the Italian whom Albert Einstein called "the father of modern science".
Galileo, who was born and studied in Pisa, first visited Rome in 1612 to share with Jesuit mathematicians and philosophers his new telescopic observations of the moons of Jupiter.
He argued that his studies proved the fallacy of the Aristotelian view of the universe and the correctness of the theories of the Polish mathematician and scholar Nicolaus Copernicus.
It was Copernicus who first theorised - a century before Galileo - that it was the earth that moved around the sun, and not vice versa.
Galileo was later attacked by Catholic theologians who held that his theories went against scripture, and was eventually tried for heresy by the Inquisition.
It was not until the reign of Pope John Paul II - nearly four centuries later - that the Catholic Church finally admitted that Galileo had been right and he was officially rehabilitated.
What could be called the Vatican's first scientific astronomical observatory was finally set up in 1789 in a building which still exists near the Apostolic Palace, called the Tower of the Winds.
A century later, in 1891, Pope Leo XIII, in an attempt to counter the persistent perception of hostility by the Church towards science, set up another small astronomical observatory on a hill behind the dome of Saint Peter's Basilica.
The Vatican has an observatory in Arizona in the US
This was abandoned, however, in the 1930s, by which time light pollution from the city of Rome prevented the study of the fainter stars, and a new Vatican Observatory with German-made telescopes was set up at Castelgandolfo in the Alban Hills, 25km (15.5 miles) south-east of Rome.
Further expansion of the Italian capital and brightening of the night sky meant that Vatican stargazers were forced to relocate yet again to a higher, less polluted observation point.
In 1981 they chose a mountaintop in the US near Tucson, Arizona, where in 1993 the Vatican Advanced Technology Telescope was completed, equipped with a new large American-made 1.8 metre mirror.