The North Star

The North Star would be a star which appears every night in the sky. The North Star would be in the northern end of the night sky. The purpose of the north star would be to serve as a sort of early game or replacement compass, which is slightly more complicated to understand and only works if you can see the sky. 

If you (the developers) want to change it up and make it different from real life, you could alternatively make it the South Star, East Star, West Star, or (to really confuse players) something like the North-East Star or South-West Star.