How can I rotate a sphere around a cube in Three.js
<p>I<code>ve seen different options to rotate objects but I don</code>t know how to apply them. I am very new to javascript. I created the cube and the sphere and managed to make the sphere rotate around its own axis but I need it to rotate around the cube  Any help is welcome. 
This is my code:</p>

<pre><code>&lt;html&gt;
    &lt;head&gt;
        &lt;title&gt;My first Three.js app&lt;/title&gt;
        &lt;style&gt;
            body { margin: 0; }
            canvas { width: 100%; height: 100% }
        &lt;/style&gt;
    &lt;/head&gt;
    &lt;body&gt;
        &lt;script src="js/three.js"&gt;&lt;/script&gt;
        &lt;script&gt;
            var scene = new THREE.Scene();
            var camera = new THREE.PerspectiveCamera( 100,    window.innerWidth/window.innerHeight, 0.1, 1000 );
            var renderer = new THREE.WebGLRenderer();
            renderer.setSize( window.innerWidth, window.innerHeight );
            document.body.appendChild( renderer.domElement );

            camera.position.z = 25;

            var loader = new THREE.TextureLoader();
            var texture = loader.load('crate.jpg');
            var geometry = new THREE.BoxGeometry( 7, 7, 7 );
            var material = new THREE.MeshBasicMaterial({map: texture});
            var cube = new THREE.Mesh(geometry, material);

            cube.rotation.x += 0.6;
            cube.rotation.y += 0.6;

            scene.add( cube );

            var loader = new THREE.TextureLoader();
            var texture = loader.load('earth.jpg');
            var geometry = new THREE.SphereGeometry( 1, 50, 50 );
            var material = new THREE.MeshBasicMaterial( {map: texture} );
            var sphere = new THREE.Mesh( geometry, material );

            scene.add( sphere );

            var render = function () {
                requestAnimationFrame( render );
                sphere.position.set(6, 0, 15);
                sphere.rotation.y += 0.01;
                renderer.render(scene, camera);
            };

            render();
        &lt;/script&gt;
    &lt;/body&gt;
&lt;/html&gt;
</code></pre>