Animation

• Use the setInterval(function, delay) and setTimeout(function, delay).

var sun = new Image();
var moon = new Image();
var earth = new Image();
function init(){
  sun.src = 'sun.png';
  moon.src = 'moon.png';
  earth.src = 'earth.png';
  setInterval('draw()',100);
}

function draw() {
  var ctx = document.getElementById('canvas').getContext('2d');

  ctx.globalCompositeOperation = 'destination-over';
  ctx.clearRect(0,0,300,300); // clear canvas

  ctx.save();
  ctx.fillStyle = 'rgba(0,0,0,0.4)';
  ctx.strokeStyle = 'rgba(0,153,255,0.4)';
  ctx.translate(150,150);

  // Earth
  var time = new Date();
  ctx.rotate( ((2*Math.PI)/60)*time.getSeconds() + ((2*Math.PI)/60000)*time.getMilliseconds() );
  ctx.translate(105,0);
  ctx.fillRect(0,-12,50,24); // Shadow
  ctx.drawImage(earth,-12,-12);

  // Moon
  ctx.save();
  ctx.rotate( ((2*Math.PI)/6)*time.getSeconds() + ((2*Math.PI)/6000)*time.getMilliseconds() );
  ctx.translate(0,28.5);
  ctx.drawImage(moon,-3.5,-3.5);
  ctx.restore();

  ctx.restore();
  
  ctx.beginPath();
  ctx.arc(150,150,105,0,Math.PI*2,false); // Earth orbit
  ctx.stroke();
 
  ctx.drawImage(sun,0,0);
}

init();draw();