Science: Fireball

At 3:38 on the morning of May 4 an eerie blue-white light flashed across a cloud-heavy sky. Seconds later, a series of explosions and tremors shook houses and rattled windows in eastern Pennsylvania, New Jersey, Delaware, Maryland. Thousands of people, startled awake, flooded police stations and newspaper offices with phone calls. What had happened? No one knew, at first.

Later that day astronomers pieced together the evidence, agreed that a bolide (the biggest kind of meteor), traveling on a west-to-east course just north of Philadelphia, must have exploded and dropped its fragments into the sea.

A bolide is the only noisy type of meteor.* It is said to move at a rate of five to 20 miles a second. As it travels, air piles up in front of it, making a windy whoosh. Air friction turns the outside of the meteor white-hot while the inside remains cold. A few seconds after it hits the earth's atmosphere, the bolide explodes with a bang.