I'm reading Phil Plait's Bad Astronomy and there are many things to learn from it! I haven't read it all, so far, but the illusion chapter is great:
Remember Steve's suggestion to look at the Moon upside down? (lowest picture).
Well, it appreas that we don't see the sky as a hemisphere but as an inverted bowl, over our heads. We see the sky as flattened: when asked to point with our arm at 45 degrees, we always point lower than that. (30 to 40 degrees). The Moon at the horizon seems bigger. There 's a Ponzo illusion that makes things that appear further, bigger, from an interpretation of the brain. Objects at our horizon appear further than the same ones above our head. They are the same size but our brain thinks they are further, so they must be bigger.

And there are plenty other examples (for instance, when a kid asks "why is the sky blue?", beware of your answer!!).
I think it's worth a conference in an astronomy meeting.

Raoul