There was a short story I read a while back in school that involved a boy who came across an alien who lived underground for so long that he was unable to see well in light. The young boy talked to the alien and the alien informed him that he left his home world for some reason. He explained that it had lush trees and grass. The alien told him that his planet was not too far from the one he is currently on (Earth). The boy was able to connect the dots and he realized that the alien was from the moon. The alien then left to go to the moon, but the boy tried to stop him before he left because his homeworld was not the same anymore.
The short story was part of a novel that contained other science fiction short stories in it. I think I read it in either middle school or highschool.