I am trying to write some sample code of three.js where i have a plane and i want that plane to rotate around.

This is my camera:

var camera = new THREE.PerspectiveCamera( 70, window.innerWidth / window.innerHeight, 0.1,  1000);
camera.position.set(50, 50, 60);
camera.lookAt(scene.position);

and this is my plane:

var planeGeometry = new THREE.PlaneGeometry(70, 30, 1, 1);
var planeMaterial = new THREE.MeshBasicMaterial({ color: green });
var plane = new THREE.Mesh(planeGeometry, planeMaterial);
plane.rotation.x = -0.5 * Math.PI;
scene.add(plane);

i have other code too but this is my render and animationframe code:

renderScene();

function cameraUpdate() {
  camera.position.x = cameraRadius * Math.cos(step);
  camera.position.z = cameraRadius * Math.sin(step);
  camera.lookAt(scene.position);
}

function renderScene() {
 //make update to position, rotation of objects in the scene
  step += 0.05;
  cameraUpdate();
  requestAnimationFrame(renderScene);
  renderer.render(scene, camera);
}

My question is that inside cameraUpdate function if dont put

  camera.lookAt(scene.position);

the rotation become very wierd and when i put this inside cameraUpdate, i get rotation of the plane in own axis which is desired !!!

My question is

1. what does scene.position mean
2. Why do i need to make camera lookat at every animation frame? i dont understand how its value get changed when camera is rotated

Thank you in advance !!!