The moon plays a symbolic and literal role in the novel, starting with the title, the Sea of Tranquility, which is a cartographic feature of the moon. This flat location is where Apollo 11 landed and where, in Mandel’s novel, the moon colonies are built: The “first colony on the moon was intended as a prototype, a practice run for establishing a presence in other solar systems in the coming centuries” (94). Someday the sun will die, or another Earth-destroying event will occur, and humanity will have to migrate further out in space to survive. Olive and Gaspery grow up under the dome of the moon’s Colony Two, or Night City, as it comes to be called. The “moonscape” (110) they inhabit is manufactured, or a simulation of Earth. Their experiences of this simulation symbolically explore what it would mean if all of human life was a simulation, perhaps one that is run because the Earth has already been destroyed.

In addition to living on the moon, several characters look up at the moon from Earth. Mirella, living in 2020, will never set foot on the moon, but it is her perspective that first introduces the moon into the novel.