Young Adult Literature, Coming-of-Age, Historical Fiction
Young Adult Literature
Well, this one's pretty easy. The main character, Mattie, is a young adult (though she seems far older than her seventeen years because of the historical context of the novel). She does young adult things, like pursue a boy, have some hanky-panky (though thank goodness it goes nowhere), and hold a steady job. She also has to contend with social disapproval and gossip, doesn't always get along with her parent, and she has to decide what to do with her life, and which direction to take for her future. All of these are clear markers of young adult literature.
Coming-of-Age
The entire novel is a giant, gradual transition from childhood to adulthood. Granted, we meet Mattie after she's already begun this transition, but we still get to see a lot of how she changes throughout the novel. She learns what birth is actually like, what love is—and what it isn't, plus she chooses her future. She agonizes over this last one, and the fact that Mattie recognizes the weight of her decision and the effects it will have on not only herself but the people she loves, indicates her ability to see beyond herself.
A classic feature of a coming of age story is that, in the end, the main character is finally an adult. And as Mattie heads into NYC to make it on her own, well, it's undeniable that an adult is exactly what she's become.
Historical Fiction
A Northern Light is sort of about the Grace Brown/Chester Gillette mystery that took place at the turn of the century, but it's more generally a realistic depiction of rural life in upstate New York at the turn of the century.
What makes the novel stand out as more than history is how it dives into the human psyche of its characters. Instead of telling us what life is like or just the facts of the murder, Donnelly gives us an intimate view of how the murder affects the people in the community, especially Mattie and Weaver, and how the difficulties of rural life in 1906 play out for individuals and the community.
And Donnelly has done her research for the novel. There really was a floating grocery store, and some of the novel's characters are real or based on real people. Donnelly even includes all her sources in the last few pages of the novel. Mattie's world is not just created out of imagination; Eagle Bay and its social context are firmly rooted in historical fact.