import flash.events.Event; stage.addEventListener(Event.ENTER_FRAME, moveMoon); var degrees:Number = 0; var radians:Number; var orbitSize:int = 200; function moveMoon(evt:Event):void { radians = degrees * Math.PI / 180; moon.x = earth.x + Math.cos(radians) * orbitSize; moon.y = earth.y + Math.sin(radians) * orbitSize; degrees++; }