Is there a way to highlight currently viewed archive?

Hi,

I have as a sidebar on one of my sites an archive (yearly) of posts from 2010 – 1999).

What I’m trying to do is have it such that if you’re in the 1999 archive page that that page in the sidebar menu appears highlight – much like you can highlight currently view pages and subpages etc.

Is there a simple way to do this? I’m using this code to draw them in:

<div id="sidebar">
<ul class="pages_sub">
<?php wp_get_archives('type=yearly&format=custom&before=<li class=\'page_item\'>&after=</li> '); ?>
</ul>
</div>