revolve/revolution:  An object revolving around a planet is moving around the planet in an orbit.  In astronomy, the phrase "to revolve" means the same thing as "to orbit."  After an object has revolved once, it is said to have completed one "revolution." 

ring:  Jupiter, Saturn, Uranus, and Neptune are each circled by dust, pieces of ice, rock and ice-covered rock.  These particles revolve around the planets near the equator and form a flat band called a ring.