False expectations

Lex's jaw dropped as he looked up into the sky with squinted eyes. It was only then that he noticed that what he had so far assumed was the 'sun' seemed to be moving in the sky.

The birds were too bright for Lex to observe them directly, but now that he was looking up in the sky, he was able to notice that there was no great ball of fire in the sky. It was only now that Mary's description of a realm had sunk in. This realm or world or large landmass, whatever it was, existed as a single entity as large as Earth's solar system. First of all, that was so much land that Lex found it difficult to comprehend. Secondly, if the entire realm existed as one landmass, how did the season's work? What was the distinction between night and day? What would happen if you kept traveling directly up? Would you hit some kind of ceiling?