Gentile here with a question about the shabbat that I can’t find an answer to elsewhere

From what I read on Wikipedia (good research, I know) the shabbat begins at sunset Friday and ends when three stars are visible in the sky on Saturday. I also know for a fact that there are never any stars visible in the sky in New York City, and that the same city has a large population of Orthodox Jews.

So my question is, how do Orthodox Jews in New York City know when to end the shabbat if they can’t see the stars?

Thanks in advance, and sorry if I’m being silly (:

EDIT: Thanks for the answers everyone!