1In the year the friar of Nola was burned, a thin man of twenty-eight came to the city of Prague with his wife, his stepdaughter, and two cartloads of household goods. He had a cough and a fever and almost no money. His name was Johannes Kepler.
2He had been a teacher of numbers in a town of Austria. But he held to the faith of Luther, and the prince of that country had ordered every such person to turn Catholic or be gone. Kepler would not turn. He would not pretend to turn, either, though it would have saved his house and his post, and others pretended. So he was on the road.
3He had weak eyes. A sickness in childhood had spoiled them, and he saw the stars doubled and smeared. He could reason about the heavens better than anyone alive. He could hardly see them.
4The house he came to was kept by a man who was his opposite in everything.
5Tycho Brahe was a Danish lord, broad and loud, with a great moustache. He had lost the bridge of his nose in a duel when he was a student, fought in the dark over which of two young men was the better at sums, and he wore a nose of metal in its place.
6And he had the best eyes in the world, and had used them as no one ever had.
7When he was young, a new star had flared up in the sky where no star had been. The learned said that could not happen, for the heavens were perfect and never changed. Tycho measured it night after night and showed that it lay far out among the fixed stars. The heavens had changed. From that night he trusted no book about the sky until he had checked it against the sky.
8A king gave him an island. On it he built a house of instruments: great arcs of brass and oak, taller than a man, with sights along them. He had no glass to look through, for no one had yet thought of it. He had only the naked eye, and patience, and the best craftsmen in the north. For twenty years, every clear night, he and his helpers wrote down where each wanderer stood. They measured finer than anyone before them, by ten times.
9Then a new king cut off his money, and Tycho left the island and came south with his instruments in wagons to serve the Emperor. He was old now, and tired. He had thirty years of numbers in bound books, a treasure with no equal on earth. And he did not have the gift to see what they meant.
10So here were two men under one roof. One had the eyes and not the reasoning. One had the reasoning and not the eyes. Each needed the other, and they could not bear each other.
11Tycho guarded his numbers like a dragon. He would let fall one figure at dinner, between the meat and the fruit, and not another for a week. Kepler was proud and poor and quick to feel insulted. He wrote the great man a furious letter and stormed out, and then had to come back and beg pardon, because he had nowhere else in the world to go.
12At last Tycho gave him one planet to work on. It was Mars, the hardest, the one that would not keep to any path the astronomers drew for it. Kepler looked at the task and laid a bet. He would have Mars beaten in eight days.
13Remember that bet.
14Before the second year was out, Tycho came home from a feast in great pain. He lay eleven days in fever. Kepler sat by the bed. In the last night the old lord's mind wandered, and he said one thing over and over, like a man making a verse. Kepler wrote it down:
15"Let me not seem to have lived in vain."
16By morning he was gone through the Last Door. Two days later the Emperor's messenger came to Kepler's lodging. He was to be Imperial Mathematician in the dead man's place. And the books of numbers were to be his to use. All of them.
17Now hear about the war with Mars.
18Everyone since the Greeks had known one thing for certain about the heavens: whatever moved there moved in circles. A circle is the perfect shape. It has no beginning and no end, and every part of it is like every other. The old canon of Frauenburg had moved the earth out of the middle, but even he had kept the circles. It was not a thing anyone questioned.
19So Kepler began with a circle for Mars, set a little off from the sun, and set to work to find its exact size and place from Tycho's figures.
20It was all done by hand. There was no quick way. Each trial meant weeks of sums, sheet after sheet, with a quill, by candle, with his bad eyes close to the paper. He made a slip and had to go back. He made another. He tried seventy times. The eight days went by, and eight months, and then years.
21At home it went badly. The Emperor's treasury was empty, and his pay was a promise. His wife Barbara had been a miller's daughter with a little money, and she watched it go. She did not understand what he did all night, and he was not patient in explaining. Children were born. Two had been buried already in the old town.
22In the second year he had it.
23He had a circle, and a way of moving on it, that put Mars in the right place at every one of the twelve times it had been caught standing opposite the sun. It matched to within two parts in sixty of a single degree. No astronomer had ever fitted a planet so well. It was better than the old canon had done. It was better than the Greeks.
24Any other man would have stopped there and printed it and been famous.
25Kepler did one thing more. He tested his circle against some other measures of Tycho's, taken at other times, that he had not used in the making.
26It missed. Not by much. At the worst places Mars stood eight parts in sixty of a degree from where the circle said it must be.
27Hear how small that is. The full moon looks no wider than a pea held out at arm's length. Eight minutes of arc, as the astronomers name it, is a quarter of the width of the moon. On the instruments of any man before Tycho, a gap of that size could not even have been seen.
28He sat with that number through a night. This much may be said of what was in his mind, for he wrote of it afterward himself.
29He could let it pass. Who would know? There was not another man in Europe who would ever check. He could say that Tycho's helper had been cold and tired on those nights and read the brass a little wrong. He could shave a figure. Two years of labour would be saved, and his family fed, and his name made.
30But he had known Tycho. He had eaten at that loud table and been shouted at by that man. He knew how those numbers had been taken: again and again, by two watchers at two instruments, checked one against the other. Tycho had boasted, and bullied, and hoarded. He had not been careless once in thirty years. If Tycho's book said Mars was there, Mars was there.
31Then it was the circle that was wrong.
32Kepler threw away two years of work. He wrote that those eight minutes showed the road to a new making of the whole of astronomy, and that since they could not be ignored, he would not ignore them. Then he began again from nothing.
33Now he had no circle to stand on. No one had ever asked what shape a planet's path might be if it was not a circle, for there had been no reason to ask. He was like a man who has always walked on roads and is set down in the middle of a moor.
34He let the numbers lead him. It took three years more. Mars went faster when it was near the sun and slower when it was far. The path was not round. It was drawn in a little at the sides, like an egg. He tried an egg shape and the sums were dreadful and still it missed. He wrote to a friend that he had cleared the stable of circles and was left with a cartload of dung.
35And then, one day, he saw that he had been looking at the answer for a year and had not known its face.
36It was the shape you make if you push two pins into a board, and loop a thread loosely round them, and draw with a pen pulled tight against the thread. A long round, an oval. The Greeks had known that curve well and had a name for it: the ellipse. No one had ever thought to look for it in the sky. Mars went round on an ellipse, and the sun stood at one of the two pins.
37He put that curve to Tycho's numbers. Every one of them fell on it. The eight minutes were gone. There was nothing left over.
38He wrote that it was as if he had woken from sleep.
39And he found the rule for the speed as well. Draw a line from the sun to the planet, and let it sweep along as the planet moves, like the hand of a clock. In equal times, that line sweeps over equal spaces. Near the sun the line is short, so the planet must run. Far out the line is long, so the planet may walk. It held for every planet he tried.
40Two thousand years of circles were finished. He had not wanted that. He loved the circle as much as any man. But the sky was not obliged to be what Johannes Kepler found beautiful, and when he saw what it truly was, he found that more beautiful still, because it was so.
41He was a believer to the root. He had meant to be a pastor, before the stars took him. He thought that the Maker had built the world by number and measure, and that to find the measure was a kind of prayer, the best he knew how to make.
42His own church would not give him its bread and wine. He could not sign every line of its rule of faith, for there was one point on which he thought it wrong, and he would not put his name to a thing he did not hold. The pastors shut him out. The Catholics would have taken him gladly, with honours, if he would only come over. He would not do that either. He stood between the two, alone, and belonged at no one's table.
43It was the same thing in him each time. He would not say a creed he doubted to keep his house. He would not shave eight minutes to keep two years. A false number hurt him like a stone in the eye.
44He called the book the New Astronomy. It took four more years to get it printed, for there was no money, and Tycho's heirs fought it. In it he did a thing few writers do. He put in all his wrong turnings. The seventy trials, the egg, the cartload of dung. He wanted the reader to see the whole road, so that anyone could walk it after him and check each step.
45And on the back of the title leaf of that book he settled an old account. He had learned who wrote the false page at the front of the old canon's work, the page that said none of it need be true. He printed the name: Osiander. The canon, he said, had meant every word.
46The year that book came out was a hard one for him, and the two after were worse. The Emperor he served was pushed off his throne by his own brother. Soldiers were quartered in Prague, and with soldiers came fever. His wife Barbara took it and died. And his favourite child, a boy of six named Friedrich, died of the smallpox in the same season.
47He wrote of the boy that he was like a hyacinth of the morning in the first days of spring. Then he packed the books of numbers once again into a cart, and went on to the next town that would have him.
48Listen. This is not a story about a clever man. It is a story about a gap one quarter of the width of the moon.
49On one side of that gap were his rest, his wages, his wife's peace, and the good opinion of the world. On the other side was a thing no one had asked him for and almost no one would understand. He looked at the gap and would not say it was not there.
50And because he would not, the sky gave up its shape to him. That is how it is given. It is not given to the one who is sure. It is given to the one who will not round off the truth.
51Tycho had not lived in vain. Nor had the helpers on the island, freezing at the brass arcs, writing figures by lantern for a purpose they never learned. They had kept faith with each night's sky. A stranger with bad eyes had kept faith with them. Between them, across the Last Door, the thing was done.
52The New Astronomy went out from the press in a small printing, and for a time hardly anyone read it. Kepler hoped most for a word from one man, a professor in Padua. Years before, they had traded letters, and the professor had owned that he too held with the old canon, in secret. Kepler had begged him to say so aloud. The professor had not written back.
53No word came now either. The professor in Padua was busy that summer. He had heard that a spectacle-maker in Holland had put two lenses in a tube.
54Now hear what came after.