Based on that description, I would not think that this book qualifies as "mathematical fiction". In my opinion, the characters are astronomers or physicists (or astrophysicists). However, the book (and its characters) frequently refer to them as "mathematicians". Moreover, the book often talks about math or uses mathematical imagery. All together, this is enough to "tip the scales" for me and has convinced me to include it in this database as (just barely) a work of mathematical fiction. (Feel free to disagree.)

Here are a few notes about the mathematical aspects:

• George (who believes in astrology and God and that ancient Babylon was in Toledo, OH) uses math in his work, but views it as an unpleasant necessity that scares people away from his field:

  (quoted from How to Tell Toledo from the Night Sky) "You know," said George, sort of wistfully, "everyone takes an astronomy course in college because looking at the stars is so cool and romantic. They get taught the constellations and everything, and how this used to be thought and that used to be believed. And then we get into calculating the distance in light-years from here to there, and everyone quits because they don't like the math. I mean forget parallax." "It's parsecs," she said quietly. "Right, parsecs, yes. But you don't get what I'm saying. I don't like the math. But I stayed with it. The math is a necessary evil, but the stars are still stars. It's still cool and romantic."

• One of the other women that George dates in his attempts to fulfill an astrological prediction is a woman who was raised without language:

  (quoted from How to Tell Toledo from the Night Sky) As a result of her limited exposure to language, she had become a math genius, just as her father had planned. She did not respond to George's advances like other girls did, but, if anything, this made him more convinced that she must be the one, the center of the target.

• The book says that Irene earned a master's degree in mathematics at Bowling Green and the original blurb for the book described her as "a pragmatist mathematician". With this in mind, I would say she is a stereotypical "soulless" mathematician that we often see in fiction, as if interest in math somehow precludes an appreciation of love, beauty, and joy:

  (quoted from How to Tell Toledo from the Night Sky) Irene was an empiricist. She believed in science, and math, and numbers. She did not believe in love, or any god. She did not believe, "Someday you will be happy." She was opposed to novels, most poetry, and dance of any kind.

• Even a sex scene is described in mathematical terms:

  (quoted from How to Tell Toledo from the Night Sky) He began to move inside her in a way that was rhythmic and thrilling, and she felt her mind tripping away. She was spinning in this world, on the point of him in her, and as she felt herself joined up with him, there in her depths, in the geometric depths of her round cervix, her mind spun again, and she saw what was entirely mathematical. A vision before her face of a circle and a point and a line, and the way they moved together, up and down, back and forth. One circle inside another circle becomes a point that moves just up and down. "It's the Tusi couple," she said to him. "It's the Tusi couple. It's happening inside me."

• A speech that George and Irene are listening to says:

  (quoted from How to Tell Toledo from the Night Sky) "But then the astronomers came and put the gods out of business. Set the sun aflame, scattered the stars across the universe, made the earth into a ball. In this crusade, we have one friend. This is mathematics....Math dispels ignorance. Math conquers discord, and anarchy, and revolution. It is math that says 6.3184 times ten to the third. Math will see us through."

  (Sorry...I don't understand the "6.3184 times ten to the third" part. I'd be grateful if someone could explain what this refers to.)