Hidden Sun, The (Magic Works)......$15.00

Two disks are placed in a box, the sun and the transparent
shadow.  The magician shakes the box, then removes the disk
with the
sun on it and places it into his pocket. When the box is
opened, instead of finding the shadow in it, your audience see
the sun
inside!  You produce the shadow from your pocket!  
How did these two disks switch places?