re: The Celestial Sphere - perspective
I can stare up at the night sky and take in hundreds of stars as if they were painted on the inside of a sphere. But it's not a sphere: some stars are further, some are closer, and the blackness between doesn't exist. Keeping this in mind as I stare at the sky, the patch of sky shrinks and I can only take in half a dozen stars at a time and find my perceptive ability stretched to its limits.