The universe is not a sphere - it just is an expanding existence. If it were a sphere, that would imply an edge, or boundary, and that doesn't exist, even though it has a size! It also has no center. We are on a planet that rotates, and revolves around the sun in a solar system that revolves around the center of our galaxy, etc., so we really can never quite look at the things quite the same way. The line of sight is never the same. Astronomycast.com has had a number of episodes dealing with how distance is measured, the shape of universe, and so forth.