# Haskell, <s>143</s> 136 bytes

This uses the [gloss](http://hackage.haskell.org/package/gloss-1.9.4.1) package:

 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