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).
So what is it? Is it a trans-dimensional portal into the future, some wormhole from the Pegasus galaxy, or two alien spaceships battling it out?
Dr. Phil Plait followed forum discussions of the event and explains how online astronomy geeks figured out the source of the sight. Link