Galileo Galilei, a Dutch optician had invented a glass that made distant objects appear larger, Galileo crafted his own telescope and turned it toward the sky. Galileo quickly discovered that our Moon had craters, that Jupiter had it's own moons, that the Sun has spots, and that Venus has phases like our Moon. Galileo, who lived from 1564 to 1642, made many more discoveries. Galileo claimed that his observations only made sense if all the planets revolved around the Sun, as championed by Aristarchus and Copernicus, not the Earth, as was commonly believed then.

The powerful Inquisition made Galileo publicly recant this conclusion, but today we know he was correct. The concept of ourselves as the center of the universe was no easier for human societies to give up than it is for individuals. Copernicus escaped censure because his theories weren't published until he was on his deathbed. Galileo, however, attracted the attention of the Inquisition, and was found guilty of heresy, forbidden to publish, and sentenced to house arrest for life. This was relatively lenient treatment for the time, perhaps meted out because of Galileo's age and poor health.

In 1600, the philosopher Giordano Bruno had been burned at the stake for espousing the same ideas. Moving the designated center of the universe from Earth to the Sun may have been the hardest step, but it was only the beginning. As astronomy progressed in the nineteenth and early twentieth centuries, we gradually became aware that our planet orbits an ordinary star tucked away in an arm of an ordinary spiral galaxy, of no particular prominence within an enormous universe. But most people don't find that discouraging. Though it turns out that we are not at the center of anything, the universe we know today has far more wonders than Ptolemy could have imagined.

Reference Sites:
http://www.scienceclarified.com/
http://www-groups.dcs.st-and.ac.uk/
http://planetquest.jpl.nasa.gov/timeline/timeline.html