Haazinu - Signs of Heaven and Earth

Why does Moshe call to the Heavens and the Earth when he begins the song of Haazinu, which is all about the covenant of Hashem with the people of Israel? What is the concept of the Heavens and the Earth being the 'witnesses,' the ones with whom Israel sins, the ones who are renewed and represent the eternity of Israel? Why are they present at the redemption of Israel, and at the miracles that Hashem performs for us in the wilderness? Why are they like the guardians of the prince who present the prince with crowns when he does good things? Why are they present as the Jewish people enter the land of Israel?