"There was some question as to whether it was a piece of space junk burning up, but it was not," said Geoff Chester, a spokesman for the Naval Observatory in Washington, D.C. "As far as I've been able to figure out, it was simply a rock falling out of the sky, as they are wont to do on occasion."
Chester said it was a type of meteor called a bolide, one that appears like a fireball in the sky, and was about the size of a small piece of luggage or a computer monitor.
Nothing unusual was detected on National Weather Service radar, and authorities also ruled out aircraft problems or military flight tests.
Witnesses along a 60-mile swath of the Puget Sound region from the Tacoma area to Whidbey Island and as far as 260 miles to the east said the sky lit up brilliantly, and many reported booms as if from one or more explosions.
Reactions by callers to CBS Radio affiliate KIRO-AM varied widely.
A man from northwest Montana described it "like a transformer blowin' up."
"I heard the rumble, and then I felt the whole house shake, and I thought, 'Oh, an earthquake, huh?'" said a caller from the Seattle area.
A trucker in British Columbia, 550 miles north of Seattle, said he saw "a flash of light. It just lit up the mountain ridges, and the first thing I thought of was al Qaeda."
"I saw this flash of light, and then I heard a pop-pop-pop and then the house kind of creaked — it was bizarre. It was kind of scary," said another Seattle-area woman calling the radio station.