Greetings, I have a problem, and I don't really know how to solve it. I'm writing a spy novel, however not in the traditional sense. It takes place in an alternate universe, however, if I don't mention it to the reader,they will be unaware of the setting. What I mean is, it doesn't take place on earth, how do I gave the reader the indication that they are not on earth? I don't want to mention earth whatsoever. I thought of dropping hits such as mentioning the time of day (nightime last longer than usual in my setting). The character himself was born on the planet, so it's not like I can use my MC as a window to this new world. How do I introduce or give the reader the sense that the story is set in an alternate universe?