Also, it was black.

Except in the vicinity of a portal, there was nothing to see when one looked in the direction of Orbitsville, There were no errant chinks of light, no reflections. As far as the evidence of the eye was concerned the familiar cosmos, which was so richly spangled with stars and galaxies and braids of glowing gas, had been sliced in half. There was a hemisphere of sparkling illumination and a hemisphere of darkness — and the latter was the stupendous, invisibly brooding presence that was Orbitsville. And even at a range of a billion kilometres, a distance which light itself took almost an hour to traverse, the sphere was awesome. It registered as a monstrous black hole which had eaten out the centre of the sky.

What, Dallen wondered, must the crew of the Bissendorf have thought when they were making that first approach all that time ago? What was going through their minds as they saw the edges of the dark circle balloon steadily outwards to occlude half the cosmos?

He could imagine those first explorers inclining to the idea that they had encountered a Dyson's Sphere. The 20th Century concept was that, in order to meet all its land and energy requirements, a highly advanced civilisation would eventually need to englobe its parent sun and spread across the inside of the sphere which had been created. A Dyson's Sphere, however, would have been a patchy and inconsistent construct, laboriously cobbled together over many millennia from dismantled planets, asteroids and cosmic debris. And it would have been leaking various kinds of radiation which would have given abundant clues about its true nature.

Orbitsville, in stark contrast, would have remained enigmatic. Its shell of ylem was opaque to everything except gravitation, and therefore the wanderers of the Bissendorf would have known only that they were approaching a sun which had somehow been enclosed within a vast hollow sphere. Their long-range sensors would have told them that the surface of the globe was seamless and as smooth as finely machined steel, but no more information would have been forthcoming.