Angles are based on the unit circle. That is, 360 degrees around where 0 degrees is to the right and 90 degrees points up. (You should know the rest from high school.)

2 special notes:

  1. Child sprite angles are relative to its parent sprite. Therefore if the parent sprite is at a 10 degree angle relative to the browser window, and the child sprite is angled at 10 degrees, then the child sprite will be at a 20 degree angle relative to the browser window.
  2. Sprites are assumed to be angled at 0 degrees when initially launched unless you have explicitly given the angle in your sprite definition.

Zero and 45 degrees