中心HTML弹出窗口

Question

我有下面的HTML POP UP窗口代码，但是我想在页面中央打开它。我如何实现此目标有帮助吗？

<img src="planets.gif" width="145" height="126" alt="Planets" usemap="#planetmap">

<map name="planetmap">
  <area shape="rect" coords="0,0,82,126" alt="Sun" href="javascript:window.open('sun.htm', 'yourWindowName', 'width=200,height=150');" >
  <area shape="circle" coords="90,58,3" alt="Mercury" href="javascript:window.open('mercur.htm', 'yourWindowName', 'width=200,height=150');">
  <area shape="circle" coords="124,58,8" alt="Venus" href="javascript:window.open('venus.htm', 'yourWindowName', 'width=200,height=150');">
</map>