At 3:33 a.m. on May 22, 2013 (just a few hours ago as I write this) in Hawaii, the sky was briefly lit up by a huge expanding bubble of light in the east. I got word of this event from astronomer Adam Draginda, who is a telescope operator at the Canada France Hawaii Telescope, located at the top of Mauna Kea.
An all-sky camera at the observatory monitors the sky for weather, and captured the event:
How cool is that? When Draginda emailed me, I remembered writing about a very similar event in June, 2011. The expanding halo seen back then was almost certainly caused by an unarmed Minuteman III missile launch, so I quickly checked the Twitter feed for AbsolutSpaceGuy, and sure enough, the exact same kind of missile was launched from Vandenberg Air Force Base in California at 13:27 UTC. Hawaii is UTC – 10 hours, which put the launch at 03:27 local time, just a few minutes before the light bubble was seen. Sounds like case closed to me.
But what exactly caused the halo? The Minuteman III is a three-stage ICBM, which can get well over 1000 kilometers in altitude. The third stage is equipped with ports on the side; when the correct trajectory is reached these ports open, dumping the remaining fuel. This expands rapidly, creating the halo. The fuel dump is very sudden, so the cloud expands as a spherical shell, like a soap bubble. This creates what’s called a limb-brightened shell; where the edge appears brighter than the middle (it’s common in shell-shaped astronomical objects as well).
Having said that, I’m still not precisely clear why the halo is bright. I think what’s happening is that the expanding shell is moving very rapidly compared to the thin air around it, because the missile is traveling so quickly at that point. The shell rams the air, causing what’s called shock excitation of the air molecules—hitting them at high speed gives the electrons in the molecules extra energy, which they then release, causing the molecules to glow.
Pretty amazing. Rocket launches have caused all kinds of amazing light shows in the past; the biggest and weirdest was the bizarre Norway Spiral in December 2009. As you might expect, they can freak people out, so I’m hoping that as we get more and better footage of these events it’ll be easier for folks to find the correct information about them! Many UFO reports are of mundane objects like Venus, Jupiter, meteors, satellites, and so on. This is hardly a mundane event, I suppose, but at least it’s easily explainable.
As always, I urge you to keep your eyes on the sky. Weird and delightful things happen all the time over your head, and if you don’t pay attention you’ll miss them. Keep looking up!