title: opengl rotate tangent to a circle
body: <p>I have an object right now which I have moving in a circle around the vertical (Y) axis. I want to <em>rotate this object so it is always aligned with the tangent of the circle</em>, how do I do this? Not sure what combination of sin/cosine/tan to use as the first argument of glRotatef...</p>
  
  <p>Thanks!</p>