"For the sky dome you trace a ray going from your eye (the camera), the ray hits a point in the object's surface, is reflected and continue until it intersects the sky dome surface. Now the direction of the ray is reversed and the colour of the pixel in the intersection point with the sky-dome is used to illuminate the point of the object's surface where was initially reflected."

I do'nt think thats geometrically sound.  I know I've heard of a Ray as being something different than a Light Ray, and in referance to a the Camera, but Cameras do'nt emit light. You need to angle you light object so that it bounces/reflects into your camera, or your scene is rendered null/black. This is sometimes confusing, but I generally think in terms of Light Rays, becasue they are a natural law of science that a render engine could'nt do without...