What is the weather vane?

This is the view from our kitchen window - always admired. I was trying to wash up a stubborn casserole pot just now (rather burnt on stuff from bubbling over) and the sinking sun had illuminated the church tower beautifully, so rushed to get my camera. I thought I would use this picture for todays blip, because it is something that has intrigued us since we moved in last year = what the hell is the weather vane? Any ideas?