2009 is the 400th anniversary of Galileo Galilei's cosmos-destroying observations and discoveries. They include the fact that Venus has phases, that Jupiter has moons, and a number of other observations that helped create modern astronomy and encouraged Galileo to support a solar-centric Copernican view, which, of course, did not make him BFF with the Inquisition, or the Catholic church, who favored the inaccurate but comforting geocentric view, which believed that the sun revolved around the earth.
In 1609, Galileo makes his first telescope, an improvement on other European models which offered 3 x views of objects; Galileo's telescope provided 20 x magnification of distant objects. Over time, Galileo refines his telescope, including discovering a way to reduce the aperture, thus allowing him to control the light entering the telescope, and reduce it enough so that very bright objects, like Jupiter, could be seen more clearly.
On January 7, 1610, Galileo turns his newly improved telescope towards Jupiter, and observes what, at the time, he thought were three stars, arrayed in a line through Jupiter. Fascinated, he continues to observe them. A week later, the fifteenth of January, his notes reveal that he had realized that there were four of the objects, not three, and that they were moons revolving around Jupiter. The four moons (four of the sixteen known moons, out of 23 satellites) are named the Galilean Moons, and consist of Io, Europa, Ganymede, and Callisto. In March of that year, his book, Siderus Nuncius, reveals his discoveries and makes Galileo famous.
Or infamous, in some circles. As Galileo becomes increasingly convinced that the sun was the center of the solar system, not the earth, the officials of the church become increasingly agitated, and Galileo's views, against a backdrop of supporting evidence from other astronomers, draw the attention of the Inquisition. In 1616 a committee appointed by Rome to report to the Inquisition declares that the idea that the sun was the center of the universe, and that the earth itself has an "annual motion," or orbit, is not only absurd, but heresy. Galileo is privately ordered by Cardinal Bellarmine, on instructions from Pope Paul V, not to discuss or write about the Copernican theory. By 1624, then Pope Urban VIII, a personal friend of Galileo, allows Galileo to write about the Copernican theory as long as he writes about it as a mathematical theory, rather than a matter of observable astronomy.
In 1632 Galileo publishes his book Dialogue Concerning the Two Chief World Systems, in which he compares and analyzes the solar-centric Copernican model against the church-favored geo-centric model. Despite granting conditional permission to publish, Pope Urban VIII is convinced by church officials to forbid the publication. Galileo, now ill and infirm, is summoned to Rome to report to the Inquisition. After 18 days of formal, rigorous interrogation, Galileo confesses that he may have made his argument in favor of the Copernican system too persuasive, and offers to tone it down in a subsequent book. The pope decides instead to imprison Galileo. Shortly thereafter, Galileo receives a formal notification of investigation by the Inquisition, including the threat of torture. He is examined again, and sentenced to prison and a life spent in religious repentance. Galileo formally recants his "errors," publicly, and is placed under house arrest in Sienna. He dies, blind, infirm, and still under house arrest, in Florence, in 1642.
In 2000, Pope John Paul II issued a formal apology for all the errors of the Church over the last 2000 years, and specifically included the trial of Galileo.