var skyBackgroundOffset = 0;

function scrollBackgrounds() {
  skyBackgroundOffset = skyBackgroundOffset + 1;
  jQuery("#header").css('backgroundPosition', function(index) {
    return Math.round(skyBackgroundOffset) + 'px top';
  });
}

jQuery(document).ready(function() {
  jQuery("#header").removeAttr("style");
  var holdTheInterval = setInterval(scrollBackgrounds, 60);
});