Galileo didn't invent the telescope, but he was the first astronomer who used it in a systematic way. His own telescope was a model he'd made himself. The things that he saw through it, and wrote about, caused a revolution in science, and a tremendous political and religious controversy.

Every day at the same time, Galileo charted the movements of the sunspots he saw through his telescope. They moved in such a precise direction that Galileo became sure the Sun was rotating on an axis. Up until this time, sunspots had been attributed to atmospheric phenomena: events that took place around the Sun, not on it.

Galileo published some letters in 1613 with his findings. They included his drawings of the sunspots. But the idea that the Sun had "blemishes" on it disturbed a lot of people, especially the leaders of the very powerful Roman Catholic Church. To them, everything in the heavens was made of an unchanging perfect substance. And anyone who didn't agree was treading on dangerous ground.

They warned Galileo not to discuss his radical ideas. But he continued to study the heavens, and became more and more convinced that Copernicus's theory of a Sun-centered universe—another belief that the Church was trying to repress—was correct. Eventually, in 1630, the Vatican officially denounced Galileo for "publishing certain letters on the sunspots" and for believing and teaching that the Earth revolved around the Sun.

Galileo had cause for concern, because in 1600, Giordano Bruno, a philosopher who supported Copernicus's theories, was burned at the stake. The Vatican gave Galileo an opportunity to renounce his ideas, and he did. Nonetheless, he was forced to spend the rest of his life under house arrest at his home in Florence. He died in 1642.

Learn more about Galileo on the Rice University Web site.

Learn more about Sunspots on the Exploratorium's Sunspot Web site.