window.onload = getbg;
function getbg()
	{
		var img;
		datetoday = new Date();
		timenow=datetoday.getTime();
		datetoday.setTime(timenow);
		thehour = datetoday.getHours();

		if (thehour > 21)
		 img = 'header-night.jpg';
		else if (thehour > 17)
		 img = 'header-sunset.jpg';
		else if (thehour > 9)
		 img = 'header-daylight.jpg';
		else
		 img = 'header-sunrise.jpg';
		
		document.body.style.backgroundImage = 'url(images/bg/' + img + ')';
		
	}