why does my side bar go to the bottom of the page?

Ok- so i am not very good with the coding or anything, but i noticed that my blog that i set up, now has the right sidebar on the bottom of the page. I have tried a few different themes (so maybe it’s my computer, i dunno) You can see what i mean at http://www.robertsteffens.net- Let me know if you need any more information.

Thanks!

Rob