Haskell, 143 136 bytes
This uses the gloss librarypackage:
import Graphics.Gloss main=animate(InWindow""(100,100)(0,0))white$ \t->color(makeColor 0.5 0 0.5 1).rotate(t*6).translate 38 0$circle 1 The prettier version is
import Graphics.Gloss purple :: Color purple = makeColor 0.5 0.0 0.5 1.0 main :: IO () main = animate (InWindow "" (100,100) (0,0)) white $ \t -> color purple . rotate (t * 6) . translate 38 0 $ circle 1