Almost every 'night' that May, as the comet was passing inside the orbit of Mars, he had checked its location on the star charts. Although it was an easy object with a good pair of binoculars, Floyd had stubbornly resisted their aid; he was playing a little game, seeing how well his ageing eyes would respond to the challenge. Though two astronomers on Mauna Kea already claimed to have observed the comet visually, no-one believed them, and similar assertions from other residents of Pasteur had been treated with even greater scepticism.

But tonight, a magnitude of at least six was predicted; he might be in luck. He traced the line from Gamma to Epsilon, and stared towards the apex of an imaginary equilateral triangle set upon it – almost as if he could focus his vision across the Solar System by a sheer effort of will.

And there it was! – just as he had first seen it, seventy-six years ago, inconspicuous but unmistakable. If he had not known exactly where to look, he would not even have noticed it, or would have dismissed it as some distant nebula.

To his naked eye it was merely a tiny, perfectly circular blob of mist; strain as he would, he was unable to detect any trace of a tail. But the small flotilla of probes that had been escorting the comet for months had already recorded the first outbursts of dust and gas that would soon create a glowing plume across the stars, pointing directly away from its creator, the Sun,

Like everyone else, Heywood Floyd had watched the transformation of the cold, dark – no, almost black – nucleus as it entered the inner Solar System. After seventy years of deepfreeze, the complex mixture of water, ammonia and other ices was beginning to thaw and bubble. A flying mountain, roughly the shape – and size – of the island of Manhattan was turning on a cosmic spit every fifty-three hours; as the heat of the Sun seeped through the insulating crust, the vaporizing gases were making Halley's Comet behave like a leaking steam-boiler.