See rickyjames commentary at http://www.sciscoop.com/story/2004/1/3/192432/8218

More visual, see picture at http://www3.sympatico.ca/hpohland/docs/Nebra.html especially at the bottom of the page.

Note that the moon is not as it is today. Also note on the lower picture, what appears to be a lake.

I have yet to find commentary on whether this is a missing piece, the result of damage, or speculation as to what it might have looked like.