<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8" />
<style>
#red {
width: 100px;
height: 100px;
background: #f00;
opacity: 0;
}
</style>
<script type="text/javascript" src="http://ajax.googleapis.com/ajax/libs/jquery/1.8.3/jquery.min.js"></script>
<script>
$(function() {
$('#red').animate(
{opacity : 1},
{
duration: 30000,
step : function() {
$('#stl').text(this.style.opacity)
}}
)
});
</script>
</head>
<body>
<div id="red"></div>
<div id="stl"></div>
</body>
</html>