The planetarium stood on a low hill at the northern edge of the town, a white dome rising above the surrounding trees, visible from the main road as a pale hemisphere against the darker colours of the hilltop, and visible from the town below as a landmark, a small white dome that caught the last of the evening light when the streets below were already in shadow. It had been built in the nineteen-sixties, when the town had been larger than it was now and when there had been money and enthusiasm for the kind of civic astronomy that a small planetarium represented. The building had been extended once, in the nineteen-eighties, and the original projection equipment had been replaced twice, most recently in the two-thousands with a digital system that could project the night sky from any location on Earth at any date in history, but the building itself was essentially the same building that had been built, the white dome still the same white dome, the hemispherical roof still the same shape against the hilltop sky.
The planetarium was open to the public four evenings a week, from Thursday through Sunday, with two shows on Friday and Saturday and one show on the other evenings, and on the weekday afternoons it was used by school groups, the primary and secondary schools of the region bringing their classes for the astronomy sessions that the planetarium's education officer ran. The evening shows were the planetarium's main public offering, the shows that the general public came to, and they were the part of the planetarium's operation that required the most preparation and the most care in the delivery, the evening audience being different from the school audience, more varied in their expectations and more in need of the particular quality of experience that a planetarium could provide.
The planetarium's director, a man named Thomas who had been running the planetarium for twenty-three years, arrived at the building at five-thirty on the evening of the public show, which gave him an hour and a half before the doors opened and two hours before the show began. He arrived at this time on every show day, the hour and a half being the time he needed to prepare the equipment and check the systems and compose himself for the evening's work, the preparation being as much mental as technical, the state of mind required for a planetarium show being different from the state of mind required for any other part of the job. He parked his car in the small car park at the side of the building, the car park empty at this hour on a Thursday, the other staff not arriving until six-forty-five, and he walked around to the front entrance, a glass door set into the white-painted wall of the building, the door locked, and he unlocked it with the key that he had carried for twenty-three years, the same key, the lock having been replaced twice in that time but the key having been replaced each time to match.