Yes, Andromeda can be seen in the northern hemisphere. Last year I looked desperately for it with my binoculars, but I couldn't find it (I probably couldn't separate it from the normal stars).
But recently I thought about aliens, and consider this:
If aliens had evolved advanced space technology and had an interstellar empire, it would be very likely that they wouldn't harm us. If they were very aggressive species, they would probably have blown themselves up in our stage where we're still on one planet and have weapons of mass destruction, like hydrogen bombs.
So we might not have to be afraid of aliens, they're probably peaceful.