I've put a green circle on the zenith--see that it right in the center of the sky map, click on it! Zenith was defined here.
If that doesn't work, probably your web browser's "imagemap" is screwed up.
You can click here to advance to the next page.
You might also email to report the problem. If possible report the name of the browser (Netscape, Internet Explorer, etc.) and computer type (PC, Mac, SGI, etc.).