apologies CS, partof it is is i'm too lazy to find my physics book and look this up properly, and it's been like a year an a half since I've had to think about this stuff.
that said, light does too have mass. i distinctly remember this. if you'll excuse me while i rummage through boxes of books, I'll check for ya.
![Wink](/tfp/images/smilies/wink.gif)