In 1633, the Roman Inquisition tried Galileo Galilei, found him "vehemently suspect of heresy," and placed him under house arrest for the remainder of his life — not for a new idea of his own, but largely for publicly defending and providing new evidence for a model of the solar system a Polish mathematician named Nicolaus Copernicus had proposed nearly a century earlier, in 1543.
An old idea, made newly dangerous by new evidence
Copernicus's heliocentric model, placing the sun rather than the Earth at the centre of the solar system, had circulated among astronomers for decades without provoking a formal church condemnation, partly because it was widely treated as a useful mathematical device for calculation rather than a literal claim about physical reality. Galileo's trouble came from doing something different: using his improved telescope to gather direct observational evidence — the phases of Venus, the moons of Jupiter — that argued heliocentrism described the actual physical arrangement of the solar system, not just a convenient calculating trick, at a moment when the Catholic Church, amid the tensions of the Counter-Reformation, was newly insistent on defending literal readings of scripture that seemed to describe an Earth-centred universe.
A conviction, a recantation, and a legend that outlasted both
Facing the Inquisition and the explicit threat of torture, Galileo formally recanted his support for heliocentrism in 1633. He spent the rest of his life under house arrest, still working — he wrote some of his most important physics during this period — but permanently barred from further publishing on astronomy. The Church did not formally lift its condemnation of heliocentrism as heretical until 1758, and Pope John Paul II did not issue a formal statement acknowledging the Church's error in Galileo's specific case until 1992.
What we're still unsure about
Historians of science still debate how much of the Galileo affair should be read as a clean story of science versus religious dogma, versus a messier conflict entangled with Galileo's personal conduct — he was famously combative and had made enemies among influential clergy and fellow scholars — and the specific political pressures facing the Church during the Counter-Reformation. Treating the trial purely as "faith versus reason" risks flattening a genuinely more complicated historical episode, and how much weight to give each factor remains a live question among historians rather than a settled morality tale.
This sits inside The Scientific Revolution, one of eight topics in Early Modern History, one of seven domains in History, one of seventeen subjects the app can quiz you on.