This amazing video was shot at an astronomical observatory in Hawaii. It’s real, according to Bad Astronomy blogger Phil Plait. In fact, there’s another camera that captures the same phenomenon from a different angle. So the question becomes, “What the hell is that?” Plait details a possible explanation, worked out by members of the Astronomy Picture of the Day forum.
… what leaps out is that the expanding halo is limb-brightened, like a soap bubble, and fades with time. That strongly points toward something like a sudden impulse of energy and rapid expansion of material, like an explosion of some kind. Note that the ring itself appears to be moving, as if whatever caused it was moving rapidly as well.
Asterix board member calvin 737 was the first to suggest it might be related to a Minuteman III missile launch around that time. As more people on the forum dug into it, the timing was found to be right. The missile launched from Vandenberg Air Force Base (in California) at 03:35 Hawaii time, just minutes before the halo was seen. I noticed the stars of Cassiopeia are visible in the webcam, so the view was to the northeast, which is the right direction to see the missile as well. OK, the timing and direction are perfect, so the rocket is clearly the culprit… but how, exactly?
[An idea posted by board member neufer] was that this was from a detonation charge in the missile’s third stage. There are ports, openings in the sides of the third stage. Those ports are sealed for the flight until the right time, when they’re blown open by explosive charges. This allows the fuel to escape very rapidly, extinguishing the thrust at a precise time to allow for accurate targeting of the warhead. At this point, the missile is above most of the Earth’s atmosphere, essentially in space. So when that gas suddenly released from the stage expands, it blows away from the missile in a sphere. Not only that, the release is so rapid it would expand like a spherical shell — which would look like a ring from the ground (the same way a soap bubble looks like a ring). And not only that, but the expanding gas would be moving very rapidly relative to the ground since the missile would’ve been moving rapidly at this point in the flight.
In his original post, Plait also explains why he thinks this is the true explanation, and why several alternate ideas don’t hold up.