The footage is from a webcam mounted outside the CFHT astronomical observatory in Hawaii (another view of it from a different webcam can be found here; sadly, both webcams are on Mauna Kea, not Haleakala). You see some stars and the horizon, then suddenly an ethereal pale arc pops into view.
It rapidly expands into a thin circular shell, then fades away as it fills the view. The whole thing takes a few minutes to expand; you can see the stars moving during the event (some of the pixels on the webcam are very sensitive and make stationary "hot spots" in the field of view).
The mysterious event initiated speculation of UFOs, wormholes, and star gates, or a ballistic missile launch.
The ballistic missile explanation has received the most credence so far. The Daily Mail claims, “[T]he most likely explanation is that is shows a U.S. Minuteman III inter-continental ballistic missile (ICBM), ejecting fuel as it enters the upper reaches of the Earth’s atmosphere. Supporting this theory, Plait points out that a “missile launched from Vandenberg Air Force Base (in California) at 03:35 Hawaii time, just minutes before the halo was seen.” So the timing of this missile launch seems to fit the time of the eerie light in the sky, but there has been no official word to support this theory.