Posted on Thursday, 15th October 2009 by Interloper
I awoke this morning to a dire warning from the JPL’s Near-Earth Objects Program: “Fireballs occur everyday,” it said. “But they are not always seen.”
Taken out of context that quote could be terrifying; in context, it’s not much better. According to a FAQ provided by the American Meteor Society several thousand so-called “fireballs” shoot through the Earth’s atmosphere every day.
Turns out, the term fireball is used to describe very bright meteors; that is, ones that appear about as bright as Venus does in the morning or evening sky. There are also “bolides”, a particular type of fireball that explode into fragments with a bright flash.
Fireballs have been reported in a number of different colours, ranging from red to bright blue and even violet. The colour of a fireball is largely determined by its chemical composition; for example, meteors containing large amounts of sodium will burn bright yellow, while those containing nickel will appear green.
Fast-moving fireballs are capable of generating sonic booms, but they may not be heard until some minutes after the fireball is actually been seen. They are also responsible for causing “electrophonic” sounds that range from the sound of static, to hissing to popping noises. Somewhat humourously, it is believed that having a large amount of hair makes it more likely you will pick up on these electrophonic effects, should they be present. I wonder how many bald scientists it took to figure that out!
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