Where It All Goes Down
Present-Day New York City
The most specific indication that the story takes place in the present day is the New York Times article about 36 questions that make people fall in love. It's a real article, published in January 2015. Given that The Sun Is Also A Star was published in November 2016, it's safe to say that Yoon wanted to tell a modern love story.
However, she steers away from superfluous pop culture references. Nobody's dabbing on the street, and Natasha's musical tastes are more 1990's grunge-rock and less 2015's "Fight Song." This lack of temporal references makes Natasha and Daniel's story feel timeless.
With the exception of a few backstories, most of the narrative action takes place on one fateful day in the Big Apple. In a city bustling with pedestrians and public transit, Natasha and Daniel are able to travel freely and have their meet-cute in the record store. If the story took place in a suburban area, two 17-year-olds would be less likely to spend the entire day gallivanting around town—and there would be fewer things to do—but it's just part of life for kids who grow up in New York.
The "city that never sleeps" provides a nice reminder that time doesn't stop for monumental events in your life, as Natasha notes when she and Daniel leave their makeout sesh in the norebang and everything seems to be shining too brightly and moving too quickly.
Placing the story in New York also allows Yoon to explore the very different neighborhoods in which Daniel and Natasha live: Daniel lives in Flushing, a well-to-do neighborhood in Queens that's full of other Korean immigrants, and he frequently takes the subway to midtown Manhattan for all his favorite foods in Koreatown.
Meanwhile, Natasha lives in a run-down area of Brooklyn. When she and Daniel visit her family's tiny apartment, she's glad it's dark outside so Daniel can't see how dilapidated her neighborhood looks in comparison to his.
The dichotomy between their backgrounds further emphasizes just how crazy it is that they met when and where they did. What else besides fate could explain why a girl from Brooklyn and a guy from Queens just so happen to be in the same part of town, at the same time, headed for the same building?
We can practically feel Natasha's eyes rolling from here.