Researchers hope to determine what killed Danish astronomer Tycho Brahe, long thought to have died of a bladder infection or possibly mercury poisoning. (Petr David Josek/Associated Press)

Astronomer Tycho Brahe uncovered some of the mysteries of the universe in the 16th century, and now, modern-day scientists are delving into the mystery of his sudden death.

On Monday, an international team of scientists opened his tomb in the Church of Our Lady Before Tyn in Prague's Old Town Square, where Brahe has been buried since 1601. After eight hours of work, they lifted from the tomb a tin box the size of a child's coffin in which Brahe's remains were placed after the only previous exhumation, in 1901.

Brahe's extraordinarily accurate stellar and planetary observations, which helped lay the foundations of early modern astronomy, are well documented, but the circumstances surrounding his death at age 54 are murky.

It has been long thought that he died of a bladder infection. Legend said it was the result of his reluctance to breach court etiquette during a reception by leaving to go to the toilet. Kidney disease was another suspect.

Tycho Brahe's extraordinarily accurate stellar and planetary observations helped lay the foundations of early modern astronomy. (Wikimedia Commons)But tests conducted in 1996 in Sweden, and later in Denmark, on samples of his moustache and hair obtained in the 1901 exhumation, showed unusually high levels of mercury. That led to a theory of mercury poisoning — even, possibly, murder.

One theory had it that his assistant, famed German astronomer Johannes Kepler, was among those to blame for his death.

Born in 1546 at his family's ancestral castle, Brahe, a Dane, was in Prague in 1601 at the invitation of the Holy Roman Emperor Rudolph II, having left his scientific observatory on the island of Hven after a disagreement with the Danish king.

Brahe's tombstone was lifted from the church floor Monday morning by archeologists. Then a micro-camera was inserted into the tomb to check its condition.

His remains were in the one-metre long box about 1.6 metres below the church floor, as expected. The box will be taken to anthropological laboratories at the Czech National Museum late Monday.

Scientists have until Friday to study the remains and take samples. The results of their analysis will be announced next year.

Wife's remains not found

Unexpectedly, however, the remains of Brahe's wife, supposedly buried by his side three years later, were not found.

Archaeologist Petr Veleminsky said the bodies of two other people were discovered in the crypt — one of a women no older than 20, the other of a child. But nothing that would belong to an older woman.

"We doubt whether his wife was really buried here," Veleminsky said.

Jens Vellev, a professor of medieval archaeology at Aarhus University, Denmark, is leading the international exhumation team, which includes scientists from Denmark, the Czech Republic and Sweden. He said he decided nine years ago to seek permission from the church and Prague authorities to reopen the tomb because there had been no proper archaeological report on the 1901 exhumation.

Vellev also hoped to gather better samples of moustache and hair — and, for the first time, samples of bone — so they could be analyzed using contemporary technology.

Vellev said the tests will include a CT-scan, an X-ray technique known as PIXE analysis and a neutron activation analysis conducted at the Nuclear Research Institute AS in Rez, near Prague. He said he thought the tests would help establish that Brahe's intake of mercury in the last weeks of his life was deadly and might have come from a painkiller containing the heavy metal.

"Perhaps we will be able to come close to an answer, but I don't think we will get a final answer," Vellev said.

He said scientists might have to exhume Brahe's remains again in 200 to 300 years to complete the research.

Scientists are interested in Brahe's skull, as well. The astronomer had part of his nose sliced off in a 1566 duel with a fellow nobleman as a student in the German city of Rostock, and the missing piece was replaced by a metal plate.

The plate was not found in 1901, but the tests now should be able to determine what it was made of — possibly a silver-copper alloy — Vellev said.

"It's been a fantastic day for us," he said. "We've been waiting so long. All of us are happy."