"Creation of the sun, moon, and planets"

This looks like it should be the moon part, but according to the Vatican Museum web page about the Sistine Chapel,

Michelangelo shows the third and fourth day of the Creation simultaneously. On the left, in fact, God, seen from behind, extends his arm towards a bush, alluding to the vegetable world. On the right, the majestic figure of the Lord reappears while, with an imperious gesture of his hands, he points and divides the sun and moon in the heavens.

The left and right parts are shown together here:

and an even broader view is here.

Top image via Miss Folly.