And over the poles aurorae crackled, an eerie fire visible even from the Moon.

Seven hours into this horror, Mikhail thought. And many more hours to go, if Eugene’s final models proved accurate. There had been some modeling of the long-term effects of all this on Earth’s climate, but unlike Eugene’s models of the sun, no precision was possible. Nobody knew what would come of this—or even if anybody could survive on Earth to see it.

But no matter what became of Earth, Mikhail could confidently predict that he would live through the day—and that was the source of his guilt.

At this moment the Moon, new as seen from Earth, had its backside squarely positioned toward the treacherous sun. So there was a wall of inert rock three thousand kilometers thick between the storm and Mikhail’s own precious skin, here on the Moon’s Earth-facing side. Not only that but the Moon, close enough to the Earth—sun line to have cast its own shadow on the homeworld today, was fortuitously protected by the shield that had been built to save Earth. So Clavius was about as safe a place as it was possible to be today, anywhere in the inner solar system.

Almost all of the Moon’s inhabitants lived on the near side anyhow, but today those few who inhabited Farside bases, at Tsiolkovski and elsewhere, had been brought to the safety of Clavius and Armstrong. Even Mikhail’s customary eyrie at the Moon’s South Pole had been abandoned, although the patient electronic monitors there continued to study the sun’s extraordinary behavior, as they would with unvarying efficiency until they melted.

And so while Earth roiled and thrashed, while heroes strove to maintain the shield, here Mikhail lurked. How strange that his career, a lifetime dedicated to the study of the sun, should come to this, to cowering in a pit as the sun raged.

But then, perhaps, his destiny had been shaped long before he was born.

As he had once tried to explain to Eugene, there had always been a deep heliophilic strand in Russian astronautics. When Orthodox Christianity had split from Rome, it had reached back to more ancient pagan elements—especially the cult of Mithras, a mystery cult exported from Persia across the Roman Empire, in which the sun had been the dominant cosmic force. Over the centuries elements of these pagan roots had been preserved, for example in the painting of sun-like haloes in Russian iconography. It had been revived more explicitly by the “neo-pagans” of the nineteenth century. These holy fools might have been forgotten—had it not been for the fact that Tsiolkovski, father of Russian astronautics, had studied under heliophilic philosophers.

No wonder that Tsiolkovski’s vision of humanity’s future in space had been full of sunlight; indeed, he had dreamed that ultimately humankind in space would evolve into a closed, photosynthesizing metabolic unit, needing nothing but sunlight to live. Some philosophers even regarded the whole of the Russian space program as nothing but a modern version of a solar-worshiping ritual.

Mikhail himself was no mystic, no theologian. But surely it wasn’t a coincidence that he had been so drawn to the study of the sun. How strange it was, though, that now the sun should repay such devotion with this lethal storm.

And how strange it was too, he reflected, that the name given by Bisesa Dutt’s companions to their parallel world, Mir, meant not just “peace” or “world,” but was also the root of the name Mithras—for mir meant, in ancient Persian, “sun” …

He kept such thoughts to himself. On this terrible day he must focus not on theology but on the needs of his suffering world, of his family and friends—and of Eugene.

Eugene’s big college-athlete body was too powerful for the Moon’s feeble gravity, and as he paced he bounded over the polished floor. Fitfully he studied the graphs displayed on the softscreens, which showed how the sun’s actual behavior was tracking Eugene’s predictions. “Almost everything’s still nominal,” he said.

“Only the gammas are drifting upward,” Mikhail murmured.

“Yes. Only that. The perturbation analysis must have gone wrong somewhere. I wish I had time to go over it again …” He continued to worry aloud at the problem, talking of higher-order derivatives and asymptotic convergence.

In common with most real-world mathematical applications, Eugene’s model of the sun was like a math equation too complex to solve. So Eugene had applied approximation techniques to squeeze useful information out of it. You took some little bit of it you could understand, and tried to push away from that point in solution space step by step. Or you tried to take various parts of the model to extremes, where they either dwindled to zero or converged to some limit.

All these were standard techniques, and they had yielded useful and precise predictions for the way the sun was going to behave today. But they were only approximations. And the slow, steady divergence of the gamma ray and X-ray flux away from the predicted curve was a sign that Eugene had neglected some higher-order effect.

If Mikhail had been peer-reviewing Eugene’s work, the boy would certainly have come in for no criticism. This was only a marginal error, something overlooked in the residuals. In fact a divergence of fact from prediction was a necessary part of the feedback process that improved all scientific understanding.

But this wasn’t just a scientific study. Life-and-death decisions had been based on Eugene’s predictions, and any mistakes he had made could be devastating.

Mikhail sighed heavily. “We could never save everybody, no matter what we did. We always knew that.”

“Of course I understand that,” Eugene said with a sudden, startling snarl. “Do you think I’m some kind of sociopath? You’re so damn patronizing, Mikhail.”

Mikhail flinched, hurt. “I’m sorry.”

“I have family down there too.” Eugene glanced at Earth. America was turning into the storm, waking to a dreadful dawn; Eugene’s family were about to feel the worst of it. “All I could ever do for them is the science. And I couldn’t even get that right.”

He paced, and paced.

One-eye was frustrated and confused.

Tuft had defied him again. When he had found the fig tree with its thick load of fruit the younger male had failed to call the rest of the troop. And then, when challenged, Tuft had refused to yield to One-eye’s authority. He had just continued to push the luscious fruit into his thick-lipped mouth, while the rest of the troop pant-hooted at One-eye’s discomfiture.

By the standards of any chimpanzee troop, this was a severe political crisis. One-eye knew Tuft had to be dealt with.

But not today. One-eye wasn’t as young as he was, and he was stiff and aching after a restless sleep. And besides it was another hot, still, airless day, another day of the peculiar gloom that had swept over the forest, a day when you felt like doing nothing much but lying around and picking at your fur. He knew in his bones he wasn’t up to taking on Tuft today. Maybe tomorrow, then.

One-eye slunk away from the troop and moodily began to climb one of the tallest trees. He was going to bed.

In his own mind he had no name for himself, of course, any more than he had names for the others of the troop—although, as an intensely social animal, he knew each of them almost as well as he knew himself. “One-eye” was the name given him by the keepers who watched over the troop and the other denizens of this fragment of the Congolese forest.

At twenty-eight, One-eye was old enough to have lived through the great philosophical change that had swept over humankind, leading to his own reclassification as Homo, a cousin of humans, rather than Pan, a “mere” animal. This name change ensured his protection from poachers and hunters, of the kind that had put a bullet into his eye when he was younger than Tuft.