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By Root 770 0

he performed observations of the Sun itself. In the Aristotelian worldview, the Sun was supposed to symbolize otherworldly perfection and immutability. Imagine the shock caused by the realization that the solar surface is far from perfect. It contains blemishes and dark spots that appear and disappear as the Sun rotates about its axis. Figure 18 shows Galileo’s hand-drawn images of sunspots, about which Galileo’s colleague Federico Cesi (1585–1630) wrote that they “delight both by the wonder of the spectacle and the accuracy of expression.” Actually, Galileo was neither the first to see sunspots nor even the first to write about them. One pamphlet in particular, Three Letters on Sunspots, written by the Jesuit priest and scientist Christopher Scheiner (1573–1650) annoyed Galileo so much that he felt compelled to publish an articulate reply. Scheiner argued that it was impossible for the spots to be right on the Sun’s surface. His claim was based partly on the spots being, in his opinion, too dark (he thought that they were darker than the dark parts of the Moon), and partly on the fact that they did not always appear to return to the same positions. Scheiner consequently believed that these were small planets orbiting the Sun. In his History and Demonstrations Concerning Sunspots, Galileo systematically destroyed Scheiner’s arguments one by one. With a meticulousness, wit, and sarcasm that would have made Oscar Wilde jump to a standing ovation, Galileo showed that the spots were in fact not dark at all, only dark relative to the bright solar surface. In addition, Galileo’s work left no doubt that the spots were right on the Sun’s surface (I shall return to Galileo’s demonstration of this fact later in this chapter).

Figure 18

Galileo’s observations of other stars were truly the first human ventures into the cosmos that lies beyond our solar system. Unlike his experience with the Moon and the planets, Galileo discovered that his telescope hardly enlarged the images of stars at all. The implication was clear—stars were far more distant than planets. This was a surprise in itself, but what was truly eyepopping was the sheer number of new, faint stars that the telescope had revealed. In one small area around the constellation Orion alone, Galileo discovered no fewer than five hundred new stars. When Galileo turned his telescope to traverse the Milky Way—that patch of dim light that crosses the night sky—he was in for the biggest surprise yet. Even the smooth-looking bright splash broke into a countless number of stars no human had ever seen as such before. The universe suddenly got much bigger. In the somewhat dispassionate language of a scientist, Galileo reported:

What was observed by us in the third place is the nature of matter of the Milky Way itself, which, with the aid of the spyglass, may be observed so well that all the disputes that for so many generations have vexed philosophers are destroyed by visible certainty, and we are liberated from worldly arguments. For the Galaxy is nothing else than a congeries of innumerable stars distributed in clusters. To whatever region of it you direct your spyglass, an immense number of stars immediately offer themselves to view. Of which very many appear rather large and very conspicuous but the multitude of small ones is truly unfathomable.

Some of Galileo’s contemporaries reacted enthusiastically. His discoveries ignited the imagination of scientists and non-scientists alike all over Europe. The Scottish poet Thomas Seggett raved:

Columbus gave man lands to conquer by bloodshed,

Galileo new worlds harmful to none.

Which is better?

Sir Henry Wotton, an English diplomat in Venice, managed to get hold of a copy of the Sidereus Nuncius the day that the book appeared. He immediately forwarded it to King James I of England, accompanied by a letter that read in part:

I send herewith unto his Majesty the strangest piece of news (as I may justly call it) that he hath ever yet received from my part of the world; which is the annexed book (come abroad this very day) of the Mathematical