Galileo used the telescope to study the heavens. He began in 1609. In March of 1610, he published a pamphlet entitled, The Starry Messenger. In the pamphlet, Galileo described his use of the telescope and how he had developed it to the point where he could see objects a thousand times larger than with the naked eye. He announced that his observation of the moon revealed that it was not smooth and spherical, as previously thought, but rough, much like the surface of the earth. This was no minor correction of a few facts. Because of the belief that heavenly bodies were made of a more perfect substance, the notion that the moon was rough and not round undermined the idea of its perfection. What Galileo effectively did was to question a whole way of understanding the universe and, by logical conclusion, a way of life.
The most revolutionary ideas were yet to come. Galileo's methodology did not included appeals to theology. Unlike Copernicus, Galileo was not concerned with theological explanations of why something was the way it was. He was simply interested in descriptions in mathematical terms through experiment and observation. Observation, hypothesis, experimentation, and mathematical description were the basic factors in this new approach. Philosophy and theology were avoided.
Traditional ways of employing metaphysics and theology were replaced by new methods of understanding the world. Even though Galileo was a loyal Catholic, he was being accused of undermining the church's authority and biblical authority. Galileo himself did not see it that way. He disagreed with the way the Bible was being interpreted by ecclesiastical authorities. Galileo questioned who should interpret the Scriptures in scientific matters. He did not think that the theologians were competent to apply their scriptural interpretation in matters of science. Over time, the result of Galileo's new method would be a severe limitation of the church's authority in many areas of human experience.
Gradually, God was less and less crucial in the explanations offered for how the world works. Galileo did not intend to reduce God. It was inevitable, however, that such would happen. The Aristotelian view that all things remain in motion as long as the cause continues to move the object meant that the motion of the planets and stars resulted from the direct intervention of God. Galileo's method proposed secondary causality, making the universe appear more mechanical. The rise of modern science opened the large question of how God acts in the world and in the universe.