From Halopedia, the Halo wiki
Movement is the twenty-ninth track (Disc 2 Track 14) included in Halo 3: Original Soundtrack. The piece was first heard in the Starry Night trailer, but it also plays in the main menu of Halo 3 and Halo 3: Mythic.
The piece begins with short choir melody. Drums and orchestra joins in and swell to an abrupt end.