I think this is a Yamaha 7' concert grand piano. I'm not sure of the length, but it sure as hell sounded great. There are a bunch of them at my school's music department, and I go there every once in a while to play.
The thinnest part of the string (and hence it's actual size) is where the photo is focused. Although piano strings have consistent width, in this picture they appear to get thicker as the photo is blurred towards both the foreground and background. This narrow depth of field was made possible by using my f/1.8 lens. There's also a slight lens flair, which makes it a little more interesting.