function rotateHeader(){
	
var headerList = new Array()
headerList[0] = "http://www.sas.upenn.edu/GAS/home/assets/img/pages/header_photo1.jpg"
headerList[1] = "http://www.sas.upenn.edu/GAS/home/assets/img/pages/header_photo2.jpg" 
headerList[2] = "http://www.sas.upenn.edu/GAS/home/assets/img/pages/header_photo3.jpg"
	
var headerImage = headerList[(Math.round(Math.random()*(headerList.length-1)))];
document.getElementById('topimage').style.backgroundImage = "url("+headerImage+")";

}