Is God a Mathematician_ - Mario Livio [32]
About 10 months ago a report reached my ears that a certain Fleming had constructed a spyglass by means of which visible objects, though very distant from the eye of the observer, were distinctly seen as if nearby. Of this truly remarkable effect several experiences were related, to which some persons gave credence while others denied them. A few days later the report was confirmed to me in a letter from a noble Frenchman at Paris, Jacques Badovere, which caused me to apply myself wholeheartedly to investigate means by which I might arrive at the invention of a similar instrument. This I did soon afterwards, my basis being the doctrine of refraction.
Galileo demonstrates here the same type of creatively practical thinking that characterized Archimedes—once he knew that a telescope could be built, it didn’t take him long to figure out how to build one himself. Moreover, between August 1609 and March 1610, Galileo used his inventiveness to improve his telescope from a device that brought objects eight times closer to an instrument with a power of twenty. This was a considerable technical feat in itself, but Galileo’s greatness was about to be revealed not in his practical know-how, but in the use to which he put his vision-enhancing tube (which he called a perspicillum). Instead of spying on distant ships from Venice’s harbor, or examining the rooftops of Padua, Galileo pointed his telescope to the heavens. What followed was something unprecedented in scientific history. As the historian of science Noel Swerdlow puts it: “In about two months, December and January [1609 and 1610, respectively], he made more discoveries that changed the world than anyone has ever made before or since.” In fact, the year 2009 has been named the International Year of Astronomy to mark the four hundredth anniversary of Galileo’s first observations. What did Galileo actually do to become such a larger-than-life scientific hero? Here are only a few of his surprising achievements with the telescope.
Turning his telescope to the Moon and examining in particular the terminator—the line dividing the dark and illuminated parts—Galileo found that this celestial body had a rough surface, with mountains, craters, and vast plains. He watched how bright points of light appeared in the side veiled in darkness, and how these pinpoints widened and spread just like the light of the rising sun catching on mountaintops. He even used the geometry of the illumination to determine the height of one mountain, which turned out to be more than four miles. But this was not all. Galileo saw that the dark part of the Moon (in its crescent phase) is also faintly illuminated, and he concluded that this was due to reflected sunlight from the Earth. Just as the Earth is lit by the full Moon, Galileo asserted, the lunar surface bathes in reflected light from Earth.
While some of these discoveries were not entirely new, the strength of Galileo’s evidence raised the argument to a whole new level. Until Galileo’s time, there was a clear distinction between the terrestrial and the celestial, the earthly and the heavenly. The difference was not just scientific or philosophical. A rich tapestry of mythology, religion, romantic poetry, and aesthetic sensibility had been woven around the perceived dissimilarity between heaven and Earth. Now Galileo was saying something that was considered quite inconceivable. Contrary to the Aristotelian doctrine, Galileo put the Earth and a heavenly body (the Moon) on very similar footing—both had solid, rugged surfaces, and both reflected light from the Sun.
Moving yet farther from the Moon, Galileo started to observe the planets—the name coined by the Greeks for those “wanderers” in the night sky. Directing his telescope to Jupiter on January 7, 1610, he was astonished to discover three new stars in a straight line crossing the planet, two to its east and one to the west. The new stars appeared to change their positions relative to Jupiter on the following nights. On January 13,