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The Scientific Revolution

The Starry Messenger

Galileo saw a number of remarkable things with his new telescope, but he not only saw them, he made careful record of what he saw and then published his findings in a book. The contrast between he and Copernicus is significant. The one feared the Church and suppressed his own book. The other believed so passionately in the truth that it never even occurred to him that there would be a problem and so rushed to press. The one worked in theories and mathematics; the other was a craftsman and an observer.

Galileo was a natural showman, with an instinct for popular appeal, and his book reflects his nature, from the catchy title to the bragging tone to the detailed illustrations. His work immediately captured attention and was soon translated.

The telescope revealed that the moon had a surface that was not smooth and perfect but was covered with hills and valleys like Earth was. This was clear evidence that the objects in the sky were not made of qualitatively different material but were shaped in some sense like Earth.

Looking at Jupiter, Galileo discovered four lesser bodies in orbit around it. This required careful and patient observation, for it is not immediately obvious to the observer that the three or four little lights near Jupiter are not merely other stars. Jupiter therefore had moons even as Earth did.

Galileo had always been an advocate of Copernicus' theory, and in observing Venus he had proof positive that he was right. Venus went through phases, like the moon did. The only way to explain the phases of Venus is that it is in orbit around the sun, that the Earth is in orbit around the sun, and that Venus' orbit lies inside our own. Galileo was giddy with triumph. He knew full well the significance of his discoveries, that he had overturned a theory that was over a thousand years old. He trumpeted his views everywhere, and condemned as a fool anyone who was not immediately persuaded.

Powerful figures within the Church were not persuaded. All through the 1620s, as religious war raged in Europe, Galileo's friends begged him to tone down his rhetoric, but he would not.