A fireball is another term for a very bright meteor, generally brighter than magnitude -3 or -4, which is about the same brightness as the planet Venus in the morning or evening sky when it is seen as being the most spectacular. A bolide is a special type of fireball which explodes in a bright terminal flash at its end, often with visible fragmentation, and occasionally even a detonation sound...after a suitable delay depending on its distance from the observer ( typically 50 kilometers or so)
The most common way that I hear about fireballs is from people who send me a report of something dramatic they have just seen in the sky. Often they wonder whether they saw a rocket explode or a satellite reenter the atmosphere. Although you can expect to see about one fireball in your entire lifetime of casual sky watching, the internet has now connected millions of people together across the globe, and it is not uncommon for me to get one or two dramatic reports of fireballs per week. I'm not just talking about a very bright meteor. Some of these reports describe the fireball lighting up the entire sky, and producing dramatic visual effects as material is explosively ablated from the incoming rock!
One place that collects this information is the American Meteor Society. They also have lots of information and statistics about video observations of meteors, radio and photographic observations and much more.
According to their estimates for fireball frequencies:
Several thousand meteors of fireball magnitude occur in the Earth's atmosphere each day. The vast majority of these, however, occur over the oceans and uninhabited regions, and a good many are masked by daylight. Those that occur at night also stand little chance of being detected due to the relatively low numbers of persons out to notice them. Additionally, the brighter the fireball, the more rare is the event. As a general thumbrule, there are only about 1/3 as many fireballs present for each successively brighter magnitude class, following an exponential decrease.
Experienced observers can expect to see only about 1 fireball of magnitude -6 or better for every 200 hours of meteor observing, while a fireball of magnitude -4 can be expected about once every 20 hours or so.
Actual sounds from fireballs can occur for fireballs brighter than -8
Only a small fraction of all meteors you will see exceed magnitude 0 which are caused by millimeter-sized meteoroids. About one in 1,200 observed meteors becomes brighter than -5 mag, while only one in 12,000 reaches -8 magnitude. The most successful time to look for fireballs is during a meteor shower, and some showers tend to be better producers of fireballs than others.
The International Meteor Organization is another place to visit to learn more about fireballs and to register your sighting..
Copyright 1997 Dr. Sten Odenwald
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