His extraordinarily accurate stellar and planetary observations, which helped lay the foundations of early modern astronomy, are well known and documented, but mystery still surrounds his sudden death.
It had been long thought he died of a bladder infection. A famous legend said it was a result of his hesitation to break court etiquette during a reception by leaving for a toilet.
But tests conducted in 1996 in Sweden and later in Denmark on samples of his mustache and hair — obtained during a previous 1901 exhumation — indicated unusually high levels of mercury, leading to a theory of mercury poisoning, even possible murder.
Jens Vellev, a professor of medieval archaeology at Aarhus University, Denmark, was leading the team of scientists from Denmark and the Czech Republic that began its work by opening the tomb in the church on Monday.