Mikhail’s interest in this place was not lunar ice, however, but solar fire.

He turned away from the shadows and began to toil up the steepening slope of the rim mountain toward the light. The path was just a trail, beaten flat by human footprints. It was marked by streetlights, as everybody called them, small globe lamps hung from poles, so he could see what he was doing.

The slope was steep, each step an effort even in the Moon’s gentle one-sixth gravity. His suit helped, with a subtle hum from exoskeletal servos and a high-pitched whir of the fans and pumps that labored to keep his faceplate clear of condensed sweat. He was soon breathing hard, and his muscles ached pleasantly: this walk was his daily constitutional.

At last he reached the summit of the mountain and emerged into flat sunlight. A small collection of robot sensors huddled here, peering with unending electronic patience at the sun. But the light was too brilliant for Mikhail’s eyes, and his visor quickly opaqued.

The view around him was still more dramatic, and complex. He was standing on the rim of Shackleton, itself a comparatively minor crater, but here at its western rim Shackleton intersected the circles of two other craters. The landscape was jumbled on a superhuman scale: even the craters’ far rims were hidden by the Moon’s horizon. But with long practice Mikhail had trained himself to make out the chains of mountains, slowly curving, that marked the perimeters of these overlapping scars. And all this was thrown into stark relief by the low light of the sun as it rolled endlessly around the horizon, the long shadows it cast turning like clock hands.

The South Pole, shaped when the Moon was young by an immense impact that had bequeathed it the deepest crater in all the solar system, was the most contorted landscape on the Moon. A greater contrast to the flat basalt plain of Tranquillity where Armstrong and Aldrin had first landed, far to the north close to the Moon’s equator, would be hard to imagine.

And this peak was a special place. Even here among the mountains of the Pole, most places knew some night, as the passing shadows of one crater wall or another blocked out the light. But the peak on which Mikhail stood was different. Geological chance had left it steeper and a little taller than its cousins to either side, and so no shadow ever reached its summit. While the Station, only footsteps away, was in perpetual darkness, this place was in permanent sunlight; it was the Peak of Eternal Light. There was nowhere like this on tipped-over Earth, and only a handful of locations like it on the Moon.

There was no morning here, no true night; it was no wonder that Mikhail’s personal clock drifted away from the consensus of the rest of the Moon’s inhabitants. But it was a strange, still landscape that he had grown to love. And there was no better place in the Earth—Moon system to study the sun, which never set from this airless sky.

But today, as he stood here, something troubled him.

Of course he was alone; it was inconceivable that anybody could sneak up on the Station without a hundred automatic systems alerting him. The silent sentinels of the solar monitors showed no signs of disturbance or change, either—not that a cursory eyeball inspection of their casings, wrapped in thick meteorite shielding and Kevlar, would have told him anything. So what was troubling him? The stillness of the Moon was an uncomfortable place to be having such feelings, and Mikhail shivered, despite the comfortable warmth of his suit.

Then he understood. “Thales. Show me the sun.”

Closing his eyes, he lifted his face toward the glare.

When he opened his eyes Mikhail inspected a strange sun.

The center of his faceplate had blocked much of the light of the main disk. But he could make out the sun’s atmosphere, the corona, a diffuse glow spreading over many times the sun’s diameter. The corona had a smooth texture that always reminded him of mother-of-pearl. But he knew that that smoothness masked an electromagnetic violence that dwarfed any human technology—indeed, a violence that was a principal cause of the damaging space weather he had devoted his own life to monitoring.

At the center of the corona he made out the disk of the sun itself, reduced by the visor’s filters to a sullen, coal-like glow. He called for magnification and could make out a speckling that might be granules, the huge convection cells that tiled the sun’s surface. And just visible near the very center of the disk, he made out a darker patch—obviously not a granule, but much more extensive.

“An active region,” he murmured.

“And a big one,” Thales replied.

“I don’t have my log to hand … Am I looking at 12687?” For decades humans had been numbering the active regions they observed on the sun, the sources of flares and other irritations.

“No,” Thales said smoothly. “Active Region 12687 is subsiding, and is a little farther west.”

“Then what—”

“This region has no number. It is too new.”

Mikhail whistled. Active regions usually took days to develop. By studying the resonances of the sun, immense slow sound waves that passed through its structure, you could usually spot major regions on the far side, even before the star’s stately rotation brought them into view. But this beast, it seemed, was different.

“The sun is restless today,” Mikhail murmured.

“Mikhail, your tone of voice is unusual. Did you suspect the active region was there before you asked for the display?”

Mikhail had spent a lot of time alone with Thales, and he thought nothing of this show of curiosity. “One gets an instinct for these things.”

“The human sensorium remains a mystery, doesn’t it, Mikhail?”

“Yes, it does.”

Out of the corner of his eye Mikhail spotted movement. He turned away from the sun. When his faceplate cleared he made out a light, crawling toward him through the lunar shadows. It was a sight almost as unusual, for Mikhail, as the face of the troubled sun.

“It seems I have a visitor. Thales, you’d better make sure we have enough hot water for the shower.” He began to pick his way back down the trail, taking care to plan every step in advance despite his mounting excitement. “This looks like it’s going to be quite a day,” he said.

Siobhan McGorran sat alone in a deep armchair. She had her personal softscreen unrolled on her lap, a cup of rather bitter coffee on the occasional table at her side, and her phone clamped to her ear. She was rehearsing the lecture she was to give to an audience of her most distinguished peers in less than half an hour.

She read aloud, “ ‘2037 promises to be the most significant year for cosmology since 2003, when the basic components of the universe—the proportions of baryonic matter, dark matter, and dark energy—were first correctly determined. I was eleven years old in 2003, and I remember how excited I was when the results from the Wilkinson Microwave Anisotropy Probe came in. I suppose I wasn’t a very cool teenager! But to me, MAP was a robot Columbus. That intrepid cosmology probe was sent off in the hope of finding a dark-matter China, but en route it stumbled over a dark-energy America. And just as Columbus’s discoveries fixed the geography of Earth forever in human minds, so we learned the geography of the universe in 2003. Now, in 2037, thanks to the results we anticipate from the latest Quintessence Anisotropy Probe, we—’ ”

The room lights blinked, making her stumble in her reading.

She heard her mother tut. “And so on and so forth,” Maria said, her soft Irish lilt exaggerated by the phone’s tiny speaker. “In time, after a lot of technical guff about this old spaceship nobody remembers, I suppose you’ll grope your way back to the point.”