需要帮助修复图像JS的动态位置

我一直在做一个JS项目,太阳围绕着一个圆圈中的图像,根据它的位置,较高的索引div将改变不透明度,使其变暗或变亮。我的问题是:;当太阳在某一点上做圆周运动时,它不再做圆周运动了。我尝试了很多方法来解决这个问题,但都没有效果。我的文档代码如下:

<style>
  sun{
    position: absolute;
    z-index: 1;
  }
  dark-light{
    z-index: 2;
  }

</style>

CSS:^JS:v

<script>



  move();

  //calls move


  function move(){
   //set rot
    var rot = 180;

    var pictureToDisplay = prompt('Please insert link to picture to     display','URL Necessary to function properly, but not required. Press enter to continue.');
    //asks user to insert picture link for STATIONARY picture
    var img = document.getElementById('img');

    if (pictureToDisplay == 'URL Necessary to function properly, but not required. Press enter to continue.'){

    }else{
    img.src = pictureToDisplay;
    }
    //Sets stationary picture
    window.setInterval( function() {

      //Repeats every 75 milliseconds forever.

      var obj = document.getElementById('sun');
    // obj. is equal to id sun
      var top = (Math.sin(rot)*500)+500;
      var left = (Math.cos(rot)*500)+500;
      //uses var rot, sine, and cosine to determine moving sun position
      var toppx = top + 'px';
      var leftpx = left + 'px';
      //adds the px after those values
      obj.style.top = toppx;
      obj.style.left = leftpx;
      //attempts to set position of obj (id sun)
      var darkToLight = -0.5+(top/500);
      //determines opacity of div using var top

      //document.write(rot+' = rot : ');

      var lightDiv = document.getElementById('dark-light');
      // same as var obj, but with the div
      lightDiv.style.opacity = darkToLight;
      //sets lightDiv to opacity
      //document.write(toppx,' ,',leftpx,' : ');


    rot = (rot+0.01) % 360;
      //moves rot up by 0.01, modulate 360
    }, 75);
    //back to top of setInterval
  }


</script>

注:我不知道JQuery。 编辑:所有的位置是绝对的,0,0是页面的左上角。我确定不去处理消极的事情。太阳对书页来说应该是绝对的,因为它什么都没有。