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?
Maybe read up on some alternative universe stories to see how they do it. When I was working on my 1st book when I was fourteen my story took place on a distorted earth - it was essentially earth just no Canada no States etc everything had been renamed and the cultures & timeframe juggled around. I didn't bother to mention that the world was any different from earth - as that's like a character saying there's something different about their world ( when he'd have no awareness of it. ) I just mentioned things to let the reader know that things were different here and stated places as though everyone should know about it. The idea is to make the extraordinary ordinary. Maybe state the longer nighttime - sort of like 1984's the clocks were striking thirteen. A plain statement but jarring image.
A lot of SF authors solved this by mentioning/describing the moon(s). Or you can mention something in the surroundings, like mobile trees.
My planet has a faint ring around it that I mention in the first scene. I made sure rings can indeed occur around rocky planets first before I used it. Two or more moons are trickier if you have an ocean and you want realism. The tides would be a little more complicated but not insurmountable to write. Ruby the Galactic Gumshoe series is a fun read that might give you some ideas.
I like what the others have suggested. Mentioning celestial bodies is the easiest way I can think of. I'm just brainstorming here. You can have it so that the planet orbits two suns. As soon as you mention two suns, the reader will know that you aren't talking about any planet in our solar system. The same goes for multiple moons.
You might also ask yourself: how quickly does the reader need to know that the setting is not on Earth? Perhaps you can let that information unfold organically as your story unfolds. Give the reader a few subtle hints to start and go from there. Even if it takes the reader a chapter or two to realize what is happening, is that bad?
I would suggest that you just write the story without worrying about this problem for now. I'll bet that it will become naturally apparent and that you won't have to go out of your way. If you do decide to go out of your way, don't make that apparent. Just mentioning something that obviously isn't true of Earth should do the job: "Sixteen continents to choose from, and I get assigned to Flerp." "I hope you've got your snowshoes." "They eat what they call 'meat'." "What's that?" "Dead animals. Heated." "You're joking, right?" "Nope."
Hrm... maybe a history buff? But we need to know why this is important. On planet Jean, there is a sign at the park gate to wipe your feet before you leave so that you don't take precious dirt away.
You're character could over hear or even watch a news story that mentions some kind of Global Event-Institution involved in something big, like some parallel United Nations.
Just show your readers the setting by letting your characters learn about stuff that sticks to the plot.
If the place and country names are all unfamiliar and the government is unlike ours the reader will get the idea.
How would a painter make the viewer suspect that the painting is not meant to be a painting of earth? By painting things on it that imply it's not an earthly locale.
A simplest little thing, like mentioning a visit to the Davis Tomb in D.C. Didn't you say "alternate", as in "this is Earth, but not our Earth"? In that case, triple moons, binary suns etc won't do the trick, because they would indicate a completely different place - and the reader would just conclude it's a space colony in the far future or some other sci-fi trope... Not to mention that, realisticaly, people living under, for example, a binary sun are likely to have a culture only distantly comparable to ours (seeing how the religious importance of the Sun plays a crucial role in human societies).
You can drop hints, like place names, or weird environmental objects, that can lead a reader to that conclusion. If interstellar travel is available, having someone read a piece of mail advertizing a trip somewhere foreign might arouse suspicions in our readers that this story is NOT on Earth. There are a few subtle ways to do it, without giving us a boring introduction or appendix.
