Then she came out into a broad open area and there it was. She thought in a sudden rush of pure thrill, I’m on the moon! Until that moment the whole journey had been in rattling metal boxes. The gray plain lapped against the distant dark maria, onetime lava seas. The Lunar landscape was not weather-beaten but sun-beaten. A billion years of full-spectrum sun had rounded edges, pounded out fine dust. Photon rain, she thought.

A strange dark Earth sat near the horizon at this high latitude. At the moment it completely covered the sun, bringing a twilight glow to the peaks of the Harbinger Mountains farther north. They had stripes of yellows and burgundies, strata of the rare earths that had been splashed up from the maria by the late-stage meteors. Their color was a welcome respite from the gray powder plains of nearly all Luna.

Earth was a black coin with a shimmering brown-red rim. Air refracted reds best, so the glowing circle danced and shone. Small white dots gave away the massive cities. People down there would see Luna gain a dusky, smoldering cast. Rachel was lucky to have her first vision here be at a magic moment, happening only once a month. Like my period, she thought. She had decided to suppress it with meds during her apprentice training, quitting only weeks ago. Had that made her think of it now? Not with foreboding, but with some zest. The suppressor had also blunted her desire.

Her translator glasses also had a closeup function. She tapped it on and watched the tiny insect scrapers atop the lava field at the edge of the horizon. Luna profited from the rich deposits of light elements and rare earths that had billions of years ago floated to the top of the cooling lava lakes. Potassium and phosphorus skimmed from the first few meters of lava, ground up and mass-separated, fed Lunar farms. The purest of it, shipped down-grav to Earth, paid for decent shared incomes.

Mass slings, driven hard along steel rails, sent payloads nearly daily down to low Earth orbit. They carried metals and rare earths, the wealth that made Luna viable; the Library was a side effect of this. Some plunged straight into deserts to slam megaton blocks home, saving on deceleration costs. Big machines dug it out, labor benefiting the poor desert regions of Africa, Asia, and middle America. Supervised robots did most of the grunt work at both ends of this 400-million-kilometer pipeline. That paid for Luna’s cities. The Library paid for its own grand towers.

Sheltering the Library from those who wanted to plunder it for the Messages meant putting it on the moon. But not the Far Side, even though that was where the most advanced telescopes ever built sat and watched the sky, free of Earthside’s radio din and its big fraction of the sky. The rare earths had decided it. The concentration of maria on the Near Side likely reflected the substantially thicker crust of the highlands of the Far Side. Those bulky ranges had formed in the slow-velocity impact of a second moon of Earth, coming in from an orbit farther out, a few tens of millions of years after the big-slam impact that had resulted in a thick orbiting disk and then Luna’s formation. Mining fed the community, and that community lived in the labyrinths of lava tubes that made the maria. The Library was a cultural edifice erected in what was by nature a rugged frontier town.