How to merge RSS feeds to display in one list on php page?


I’m trying to set up a script to combine more than one rss feed and display the posts in date order on a web page.
I can get this working with one rss file using the script below. Can someone please tell me how I can adapt this code so that it will work using an array of rss files please?

Thanks for any help in advance with this.

    $rss = new DOMDocument();
    $feed = array();
    foreach ($rss->getElementsByTagName('item') as $node) {
    $item = array (
    'title' => $node->getElementsByTagName('title')->item(0)->nodeValue,
    'desc' => $node->getElementsByTagName('description')->item(0)->nodeValue,
    'link' => $node->getElementsByTagName('link')->item(0)->nodeValue,
    'date' => $node->getElementsByTagName('pubDate')->item(0)->nodeValue,
    array_push($feed, $item);
    $limit = 10;
    for($x=0;$x<$limit;$x++) {
    $title = str_replace(' & ', ' &amp; ', $feed[$x]['title']);
    $link = $feed[$x]['link'];
    $description = $feed[$x]['desc'];
    $date = date('l F d, Y', strtotime($feed[$x]['date']));
    $day = date('d', strtotime($feed[$x]['date']));
    $month = date('M', strtotime($feed[$x]['date']));

    echo '<div class="entry clearfix">';
    echo '<div class="entry_c">';
    echo '<div class="entry_date">';
    echo '<div class="day">'.$day.'</div>';
    echo '<div class="month">'.$month.'</div>';
    echo '</div>';
    echo '<div class="entry_title"><h2><a href="'.$link.'">'.$title.'</a></h2></div>';
    echo '<div class="clear"></div>';
    echo '<span class="page-divider"><span></span></span>';
    echo '<div class="entry_content">';
    echo '<p>'.$description.'</p>';
    echo '</div>';
    echo '</div>';
    echo '</div>';
    } ?>

Do these rss feeds feeds conform to the same standard are all they all different? (atom, rss1, rss2 etc)