function prepare_images(){
sunrise1 = new Image;
sunrise2 = new Image;
sunset1 = new Image;
sunset2 = new Image;

sunrise1.src = 'http://rockhopperpost.com/images/cc/vaportrailclark/sunrise_after001.png';
sunrise2.src = 'http://rockhopperpost.com/images/cc/vaportrailclark/sunrise_before001.png';
sunset1.src = 'http://rockhopperpost.com/images/cc/vaportrailclark/sunset_after001.png';
sunset2.src = 'http://rockhopperpost.com/images/cc/vaportrailclark/sunset_before001.png';
}