"'If I Forget Thee, O Earth . . . "' starts off by introducing Marvin, a ten-year-old boy. Marvin and his father walk quickly through a large building, which includes a greenhouse and an observatory, then enter an airlock chamber, where they get into a scout car and drive outside. Before now, Marvin has only seen the outside in photographs and on television. At this point, Clarke has not revealed where they are, but he starts to give clues that they are not on earth as soon as Marvin and his father leave the airlock. The sun is moving across a completely black sky, a sight not possible from earth due to earth's atmosphere. When the sky is black on earth, it is because the sun has set, in which case the moon comes out. Also, Marvin has read about the classic rhyme "Twinkle, twinkle, little star" in one...