sphere: A sphere is a three-dimensional figure. All points on the surface of the sphere are equally distant from the point at the center of the figure.
spoke: The dark lines that stretch across the ringlets of Saturn's B-ring are called spokes. They sometimes move rapidly across the ringlets, then fade out. Scientists think the spokes are caused by dust particles hovering over the ringlets. They may be held in place by Saturn's powerful magnetic field.
