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Fireball - Background information

 

Online Fireball Report

Sky lanterns are commonly mistaken for fireballs. These are in fact small hot air balloons that are often released in large numbers at celebrations. Find out more about lanterns HERE.


A fireball seen in Mexico

A "meteor" is the correct name for what are commonly known as "shooting stars" or "falling stars". From a dark clear moonless sky away artificial lights you can expect to see one meteor every 10 minutes. Most are as bright as the stars you can see in the sky. There are more faint meteors than bright ones. The brightest star in the sky is Sirius. The planet Venus can outshine Sirius by about a factor of 15 in brightness. Venus is the brightest 'star-like' object that can be seen, thus a special name was given to meteors that are brighter than Venus because if you know how bright Venus is you can say if a bright meteor is brighter than Venus, which itself is an impressive sight to the naked eye. We call any meteor brighter than Venus a "fireball".

Your average meteor is no bigger than a grain of sand. When it collides with the Earth the closing speed can be of the order of 100,000mph and the friction with the thin air 100 miles above the ground quickly heats the tiny particle until it vapourises in a fiery streak which we call a shooting star and that typically only lasts one second or so. Most meteors are caused by small particles of dust that were left behind by comets. The brighter meteors come from larger particles. Fireballs are probably caused by objects the size of a pea, and larger. Comets leave very few large particles behind them so most fireballs probably come from pieces smashed off asteroids as the result of something (probably another asteroid) colliding with an asteroid, probably millions of years ago. Most asteroids orbit the Sun between the orbits of Mars and Jupiter i.e. between 2 and 4 times the Earth's distance from the Sun. Compared to planets, most asteroids are small (only a handful are bigger than 100 miles across) but they are rocky and some have metal cores.

There is a very rough rule of thumb that if a fireball is brighter than the Full Moon then some part of it can survive the re-entry process and land on the Earth. Such objects are thought to be as big as say an apple. How much survives down to the ground depends on lots of things like the speed of re-entry, whether its made of sturdy material like metal or light rock.

Fireballs are quite rare and the brighter they are the rarer it is to see them so you were very lucky to have seen such a bright fireball. If the fireball was brighter than the Full Moon then it is well worth looking for a meteorite (the part that survives the fall to Earth). Only 2 were found on this island in the 20th century:1969 across Northern Ireland and 1999 in County Carlow.

We will be writing a report for our magazine and investigating the likely landing zone so your help by completing the Online Fireball Report would be appreciated.

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