Hack Of The Night : Something to help clean your tarnished pots and pans

If you use copper pots and pans in your kitchen, you've probably noticed that they can get tarnished over time.  I'm sure there's a scienc-y type reason for why that happens, but I didn't study science, I went into radio.  A much smarter person that I would probalby know why this happens.  Maybe you even know..  It looks like they don't have to stay that way though.  You can use this to clean them and make them good as new again..