Rename Layer 1 "Earth and Sun". Then, on layer 1:
Place an instance of your sun movieclip near the center of the stage (I used a 400x300 pixel stage and made both the sun and earth 60x60 pixels).
Place an instance of the earth clip halfway between the sun and the right border of your movie. Give the sun an instance name of ball1 and the earth and instance name of ball2.