function countdown_clock(Unix_Time)
         {
         //I chose a div as the container for the timer, but
         //it can be an input tag inside a form, or anything
         //who's displayed content can be changed through
         //client-side scripting.
         html_code = '<div id="countdown"></div>';

         document.write(html_code);

         countdown(Unix_Time);
         }

function countdown(Unix_Time)
         {
         Today = new Date();
         Todays_Unix = Math.round(Today.getTime() / 1000);
         Time_Left = Unix_Time - Todays_Unix;

         if(Time_Left < 0) {
            Time_Left = 0;
	    var countd=document.getElementById("countdown");
	    countd.innerHTML = "<font color=\"#FF0000\">ISS is over you!</font>";
	 } else {

		//More datailed.
		days = Math.floor(Time_Left / (60 * 60 * 24));
		Time_Left %= (60 * 60 * 24);
		hours = Math.floor(Time_Left / (60 * 60));
		Time_Left %= (60 * 60);
		minutes = Math.floor(Time_Left / 60);
		Time_Left %= 60;
		seconds = Time_Left;

		dps = 's'; hps = 's'; mps = 's'; sps = 's';
		//ps is short for plural suffix.
		if(days == 1) dps ='';
		if(hours == 1) hps ='';
		if(minutes == 1) mps ='';
		if(seconds == 1) sps ='';

		//document.all.countdown.innerHTML = days + ' day' + dps + ' ';
		var countd=document.getElementById("countdown");
		countd.innerHTML = 'Next pass over you in <br />' + hours + ' hour' + hps + '<br />';
		countd.innerHTML += minutes + ' minute' + mps + '<br />';
		countd.innerHTML += seconds + ' second' + sps;

	 }

         //Recursive call, keeps the clock ticking.
         setTimeout('countdown(' + Unix_Time + ');', 1000);
         }