Nothing unusual was detected on National Weather Service radar, and authorities also ruled out aircraft problems or military flight tests.
Toby Smith, a University of Washington astronomy lecturer who specializes in meteorites, told The Associated Press that scientists were looking into the cause of the skybursts reported over a wide area about 2:40 a.m.
Witnesses along a 60-mile swath of the sound from near Tacoma to Whidbey Island and as far as 260 miles to the east said the sky lit up brilliantly, and many reported booming sounds as if from one or more explosions.
Weather service officials at Sand Point in north Seattle said there was no storm or other meteorological activity that could have produced the skybursts.
Jay Neher, a weather service meteorologist, said the agency's radar on Whidbey Island showed nothing unusual but added that the dish could have been pointed at another part of the sky at the time and could not detect objects above about 20,000 feet.
Duty officers at the Federal Aviation Administration and the Whidbey Island Naval Air Station said they knew of no civilian or military airplane problems.
Civilian pilots reported seeing the flash from Ellensburg, east of the Cascade Range, said an FAA duty officer who did not give her name. She also said one or more meteorites - meteors that hit the Earth - could be responsible.
At Whidbey Island, Petty Officer Andrew Davis said he and others on the base about 40 miles north of Seattle saw the skyburst.
"It made a pretty big bang," Davis said. "We thought it could maybe be a meteorite or something."
In Coeur d'Alene, Idaho, about 260 miles to the east, Dick Haugen said he was driving to work at KVMI Radio when he saw a flash that he took to be lightning about 2:40 a.m. - then learned there were no lightning storms anywhere in the region.
Ralph Gaume, head of astronometry at the U.S. Naval Observatory in Washington, D.C., said he knew of no likely source from outer space, such as a passing comet or meteor cluster or shower, but added that meteors commonly appear at random. Another possibility, he said, would be "space junk" such as spent rocket engines or satellites falling from Earth orbit.
Astronometry is the branch of astronomy that measures the size and location of celestial objects.
See Videos Of The Meteor Flash
Montage of different video shots from various locations -- komonews.com/qt/meteor_flashes_060304.mov (Quicktime Movie)
Two separate security camera views from Harborview Medical Center -- Version 1 and Version 2.
The Skinny On Meteors/Meteorites
By: Scott Sistek, KOMO Weather Producer
As the officials noted, it seems it was a meteor explosion that caused the bright flash. Why do they occur?
There are trillions of dust particles and tiny rocks floating in outer space. The good news is, the Earth's atmosphere protects us by making sure those objects burn up before they reach the ground.
Some of the particles are moving at a very fast speed, plus the Earth is moving at roughly 67,000 mph as it orbits the sun. As the object goes from the void of outer space and enters the outer fringe of the atmosphere, the friction from the air resistance causes the object to heat up -- much like how your foot feels warm when you drag it along a carpet.
The combined speed of the object plus the intense amount of braking force the Earth's air provides causes the objects to heat to incredible temperatures, burning them up before they get anywhere near the ground.
However, if the objects are larger, it can take longer for them to burn up. What might have happened here is you had a rock or something that was large enough so that instead of disintegrating in the first seconds when it hit the atmosphere, it managed to survive in one piece quite a ways until its temperature reached a critical point and the rock just exploded in the sky. That would also explain the thunderous sounds, and why there was a significant delay between the flash and the boom (sound travels at only 700 mph, and figure 5 seconds for each mile away.)
You can see this general process any time there's a meteor shower. Those occur when the Earth enters dust trials from past comets and those tiny particles burn up upon reaching the atmosphere, making those gorgeous streaks across the sky. Sounds like this object might have been larger, though.
In checking, we are in the initial stages of a weak meteor shower -- the June Aquilids -- but there's no word if the two events are related.
There are rare occasions when the rocks survive the atmosphere and can strike the Earth's ground (those would be called "meteroites") but we don't have any reports of that happening in this case.
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