How to change the position of jquery dialog box into center?

How to change the position of jquery dialog box into center?

I have a jquery dialog box where I am showing the content of a DIV. But
the problem is the dialog box is appearing at the bottom of the page
whenever the link button is clicked as the link button also at the bottom
of the page but I want this to appear at the top of the page so that user
don't have to scroll down to find the dialog box.
Here is my aspx code:
<a href="#" onclick="OpenDialog('#divNominees','Add Nominee')">
Jquery code:
function OpenDialog(obj,title) {
$(obj).dialog({ title: title, modal: true })
$(obj).parent().appendTo($("form:first"));
var p = $(obj).parent();
}
I would appreciate most if someone help me out of this because I already
wasted a whole morning for solving this issue.
Thanks in advance.