var day_of_week = new Array('Sunday', 'Monday', 'Tuesday', 'Wednesday', 'Thursday', 'Friday', 'Saturday');
var month_of_year = new Array('January','February','March','April','May','June','July','August','September','October','November','December');
var mon_of_year = new Array('Jan','Feb','Mar','Apr','May','June','July','Aug','Sept','Oct','Nov','Dec');

var DAYS_OF_WEEK = 7;
var DAYS_OF_MONTH = 31;

function dates_numberOfNights() {
	var diff = new Date();
	diff.setTime(departure.getTime() - arrival.getTime());
	var timeDiff = diff.getTime();
	var myNights = Math.round(timeDiff / (1000 * 60 * 60 * 24));
	if (myNights <= 0) return null;
	return myNights;
}