He"d never gotten the regret rightminded away. The brain bleachers could have fixed it for him, made it not hurt anymore. The way they had my mam leaving, for me, when I asked.

"Call every day," he said. "Or if you don"t have the bandwidth, send email." He stood, and got that particularly Irish rising stress in his voice as he said, "And don"t you be afraid to ask for help if you need it. Anywhere in the world, we"ll get you home."

"I love you, Dad." It was all I could say.

He stood up. He kissed my hair on the way out of the room.

Dearest Shaun, I don"t know how to start this letter, and I hope you won"t think I"m an awful person for doing this. In fact, I think I"m an awful person, but I would rather you didn"t. Still, I"ll understand if you do.

I"m leaving. I"m going to get a job on a ship if I can and see the world.

This isn"t because I don"t love you. I love you more than anything. But I can"t do what my father did.

I know I can"t expect you to wait for me when I don"t know when I"m coming back. But I will wait for you until you tell me not to, and when I do come back, I"ll bring you stones from every port I call in.

I love you, Billie I didn"t email Shaun the letter until morning, when I was packed and ready to leave for the station. I didn"t take much-some trousers, some shirts, a tube of sunblock. My Omni. I was wearing the jumper Dad had pushed out of the way.

I walked up Bridge Street to the train station via the footpath with the River Bracken on my right, locked away down in its stone channel with the valerian and ferns and ivy growing from the gaps in the rock all around. The path leads up a little rise behind the seawall, overhung with flowers and with a wooden rail on the right. I was pa.s.sing through the narrow stone doorway, the train station on the right, when I heard running feet behind me and a breathless voice call, "Billie Rhodes, you stop right this instant!"

I stopped, because I couldn"t do otherwise. Clutching the strap of my backpack with my right hand, I said, "Shaun, you shouldn"t have come."

I didn"t turn back to look at her. I couldn"t. Not until she came pelting up the path toward me, put her hand on my shoulder, and spun me around. Her cheeks were bright with running. She was wearing jeans and a pajama top, and her feet were bare. She minced a little, as if she had bruised the right one on a stone.

"Aw, Shaun," said I.

She put her fists on her hips, the wind raveling her tangled hair across her face. She stood framed in the gray stone door and spat, "What on earth were you thinking?"

"Shaun-" There was nothing I could say, really. Nothing that would make it better at all. The air was full of the rank, stuffy smell of valerian and the tang of the sea. It had stopped raining for once, though her hair was damp, and the broken clouds piled up and tossed behind her.

I sighed and said, "I"m sorry."

"I"m sorry. That"s all you"ve got?"

I shrugged. I hated myself for shrugging. I did it anyway.

She tilted her head. She wasn"t crying, but that was only because she was too angry. Unshed tears glistened in the corners of her eyes. "Will you at least tell me why?"

What"s out there that"s more important than me?

"I want to do something that matters," I said.

Something in her face changed. Softened, as if she couldn"t hold on to her anger. She started to say, And you can"t do that here?-I could see her start to say it. And then she paused, swallowed it, and said instead, "I don"t matter?"

"You matter most of all. But you"re not something I do, love. You"re your own thing. Your own person. What am I supposed to do about what I need?"

"Get it rightminded out," she said, so fast I knew she"d been thinking about it.

"But it"s me."

"But it hurts you. It hurts me." She shook her head, not understanding. "If it hurts you-"

"You could come with me," I replied.

She stepped back.

I nodded. "Exactly. You don"t want to. But you could get that changed, too."

She looked down. Stalemate. "So you"re leaving me."

"I"m not," I said. "I"m leaving Ireland. I"ll only leave you if you don"t want me anymore. We"ll have the cloud, we"ll have mail. I"ll come home. Maybe while I"m gone you"ll find something to be as well."

The light was climbing up the wall behind me. In the distance, I heard the whistle of the solar train. Once they had run every few minutes-but now, if I missed this one, the next wasn"t until the afternoon-and the tickets were expensive. It didn"t matter. I stepped closer to her and pulled her into my arms. "We"ve always been trapped together," I said. "We could rely on that. Don"t you want to see if we can still rely on each other if we"re not trapped?"

She leaned her head on my shoulder. Her back and arms stayed stiff and her weight wasn"t behind the caress. "We"d have to ... choose each other."

"And fight for the choice," I agreed.

She drew back. She looked at me with her dark eyes, and I realized that her ancestors-at least some of them-had come to Ireland from some faraway place, bringing that lovely skin and her beautiful straight black hair. She was Armenian on her mother"s side, but I"d never thought about what that meant.

My ancestors had come here, too, with their red hair and pale faces, from Denmark, a thousand years before hers. Travelers, explorers still.

"We can do this," I said.

She kissed me.

Stella Nova Prague. 1601.

Nefrustra vixisse videar.

The dying man turned his head and vomited into an enameled basin held by his common-law wife. "Sophie?"

"Sophie is not here, Tyge. She is with Eric. In Hamburg." Kirstine"s golden hair glimmered in the sickroom light, dimming as she bent into the shadow of the tapestried bed. "Tyge, my love, you must rest."

She cooled his brow with a cloth. His forehead rose high over a beard that would have been trimmed to a neat point were it not matted with sweat and vomitus. The bridge of his nose glittered even in the halflight, where a dueling scar lay concealed beneath a plate of precious metal.

His bulk rolled back on the bed. "I cannot sleep. Kepler. Where is Kepler?"

"I am here." Staring eyes over a prominent nose leaned from the shadows near the door. A much younger man, this-perhaps on the cusp of his thirtieth year, or just past it-his thick goatee still black. "What do you require?"

The sick man"s breath struggled in his throat. "Nefrustra vixisse videar."

"I have written it already, Tycho." Johannes Kepler raised the long quill in his scarred and cramped right hand and bent further into the light to read back the words, in the Latin and in the vernacular. ""May I not seem to have lived in vain." It is written, and you have not. I will continue our War with Mars. Your name will live."

Tycho Brahe lay dying for eleven days. Duelist, glutton, scientist: he was fifty-seven years old.

"Sophie," he whispered again, and then, "Kirstine."

Stella mortis. Stella nova.

I am dying. Like a star. I am dying.

The Heavens are not immutable. A red star crawls across the darkness that occludes my vision, no star at all. A planet. Mars. Always Mars.

No. Not always Mars. There was something before Mars.

November eleventh, the year of our Lord 1572. Walking from the warm closeness of another aristocrat"s ball into the cold of the night, I looked into blackness and the shining double-chevron of Ca.s.siopeia. I blinked, squinted, and rubbed chilled fingers against the oiled plate covering my nose.

When I opened my eyes, the strange light still shone. "Sophie! Sophie!"

My clever sister leaned her cheek against my pointing arm. A shiver trembled her body. "Oh."

"You see it."

"Tyge, I do."

A comet without a tail blazed overhead, marking Ca.s.siopeia"s waist like a jewel in her navel. "Sophie. What do you see?"

"A new star," she answered, before caution took hold and she qualified, "or a comet."

We are taught that the Heavens are divinely wrought-the fixed stars cannot move, cannot change-and aligned in the outermost of the several crystal spheres which make the Heavens. The innermost spheres support the course of the planets. The clockwork of G.o.d, so we are taught. Immutable.

So Aristotelian doctrine ordains.

Half-afraid the bright, fragile thing would vanish before we could measure it, we hurried to our makeshift observatory. There, with our inadequate tools-the Ptolemaic ruler, the various quadrants, the armillary instruments-we calculated azimuth and horizon while the new star gleamed in the Heavens as if it had always been. Impossibly, over the course of weeks, it did not move against the farther stars, and the moon pa.s.sed before and not behind it. What a gift, what a gift, what a gift.

My Lord, what are you teaching me?

"What is wrong?" Sophie asked one night, in the bitter November cold of the observatory balcony. I leaned down to a small bra.s.s quadrant on the marble railing, holding a candle alongside so I might read the minutes of arc aloud. Flickering light glittered on the fine lines dividing the curve, ran along the length of the rod pointed at the center of the new star.

A star by then bright enough to see through daylight, shining white as an angel"s halo, the faintest orange tint having become evident over the preceding days.

"These are too coa.r.s.e, Sophie. I need finer measurement: a minute of arc, less. I need a bigger quadrant." I pounded the rail, unsettling the quadrant and then cursing my childishness.

Sophie laughed at me, sketching numbers easily, more accurate than any boy a.s.sistant. A mind fine as any man"s, my sister-a mind rich in understanding of iatrochemistry, alchymie, horticulture, medicine, astronomy. Would that she had been born a philosopher and not a girl.

She set her notes and her quill aside on a low inlaid table, beside the pitcher of wine and some cakes laid on a precious jade-green plate from the Orient. She crossed the bright tiled surface of the balcony, her breath hanging white in wintry air. "Tyge. We"ll find a way."

My thumb worried the itching plate on my nose; my cheeks burned numb with cold. "These measurements are too crude to prove G.o.d"s gift, this novel thing. Your Stella nova."

"What do you need, Tyge?"

"We need to prove it"s fixed in the heavens, as the stars are fixed."

"That the heavens-Oh." She put her hand to her mouth, as the heresy of what she"d been about to say sank in. And then she nodded, and laughed at me, and said, "Well, pack your things."

"Now? In the middle of the night?"

She caught my hands in her own and spun me twice before I collapsed onto the granite bench. "The parallax!"

Of course, I thought, and clapped my hands. "You want to see if Stella nova moves against the starfield when we move upon the earth-and thus judge how far away it lies."

And she smiled like Athena in the darkness.

So we traveled, my little Sophie and I, and corresponded with astronomers from so far as England to compare our observations.

There was no parallax. It was a star-far from Earth as the rest of the fixed Heavens-a star and not a comet. The comet that proved it-the comet that moved against the fixed stars as a comet should, the comet that exhibited parallax from one Earthbound place to another-that comet was gifted to us in the year of our Lord 1577.

Our observations proved that the comet also was affixed farther from the Earth than is the moon. They suggested also that the path of this particular light through the Heavens could not be circular, but must be elliptical, elongated-and how could such a thing pa.s.s through the Aristotelian spheres? Unless those spheres did not exist?

The Heavens are not fixed, immutable. How can I express what that signifies? It shattered a thousand years of natural philosophy; it gave the final proof of the primacy of science by experiment. It proved Copernicus and his perfect solids wrong, once and for all. The Heavens are not fixed.

My book was published in 1573, before the bright new star faded into darkness forever. Before the proof of the comet.

My book, De Stella Nova.

Vocatus atque non vocatus, deus aderit.

Kepler emerged from the store-room, a blue gla.s.s bottle in his hand, sealed with wax. "Give him this to drink, Kirstine."

"What is it?" She took it from his hand, holding it up to whatever sun crept through the drapes as if she could read the nature of the world in how the light shone through the bottle.

"His own formula. Make sure he drinks the whole bottle."

"What is in it?"

"More of the same. Cardus benedicta, myrrh, pearls and sapphires. Quicksilver and opium. It will ease his pain and provoke urination."

"Is it dangerous to use so much?"

"As dangerous as it is not to. Perhaps it can clear the obstruction from his bladder." Kepler smiled. "In any case, I shall see to it, Kirstine-you have my solemn vow that his work will live on. Even if he pa.s.ses, his legacy-will be born out of that death."

Kirstine"s gaze went to the majestic bulk under the twisted coverlet. Kepler watched her, the tears seeping down her cheeks, and then turned back to Tycho. Rich silks and clean linens swaddled him, and it would make no difference in the end. Kepler might have wondered what memories darkened Kirstine"s brow as she comforted the man who loved her twenty-eight years, when no church would sanctify the union of n.o.ble to commoner. She wept, and Kepler crouched on his stool, quill poised over vellum.

Until Brahe stirred again. "Kepler."

"Kepler hears you," the mathematician said. He rose from his place at the edge of the room like a lean, richly-dressed raven and placed an ink-stained hand on Brahe"s sweating forehead.

Too-bright eyes cleared. "The new star. The comet. G.o.d in His grace ensures serendipity. He gives us what we need to discover what we must. Do you understand? G.o.d shows us what He wants us to learn. Vocatus atque non vocatus, deus aderit. Seen and unseen, G.o.d Is. His hand hangs over the world."

Kirstine collapsed into the brocade-cushioned chair. She breathed in and then out, looking hopelessly at Kepler, who shook his head.

"Call a priest. I will wait with Tycho."

"Sophie," Brahe muttered as Kirstine left. His face turned blindly from the dim light seeping through the curtains, and Kepler rose to draw them tighter. "Sophie is with her fiance. With Eric Lange, in Hamburg. She is well."

"She must not marry that wastrel." Brahe coughed wetly, suddenly lucid. "She must continue her studies."

Kepler held a goblet to his teacher"s lips. "She is a woman, Tycho. Let her have a woman"s life."