php date to seconds

function seconds2human($ss) {
$s = $ss%60;
$m = floor(($ss%3600)/60);
$h = floor(($ss%86400)/3600);
$d = floor(($ss%2592000)/86400);
$M = floor($ss/2592000);

return "$M months, $d days, $h hours, $m minutes, $s seconds";
}

<?php
$str = 'Tue Dec 15 2009';
$timestamp = strtotime($str);
echo $timestamp;
//output: 1260831600
?>