About meteors

A meteor or “shooting star” is produced when an interplanetary dust particle (meteoroid) enters the Earth’s atmosphere and deflagrates, leaving a train of excited and ionized particles along its path. If sufficient light is produced by the subsequent de-excitation, as well as various ionic processes, the meteor may be observed visually. Meteors can also be detected using techniques that rely on the scattering of radio signals by free electrons in their wakes.

The typical visible meteor is about the size of a grain of sand; a meteor the size of a grape produces a very memorable fireball. In general, meteors appear in the upper atmosphere, at an altitude of between 80 and 120 km and disappear between 60 and 80 km above the Earth.

Many meteors are sporadic, but many more are members of showers. The origin of sporadic meteoroids is still uncertain. They are probably very minor streams of low particle density, the remains of minor streams that have long dispersed, as well as solitary particles travelling in isolation. Under ideal conditions, about 10 sporadic meteors can be seen per hour.

A meteor shower occurs when the Earth intersects a stream of meteoroids that has formed as a result of the disintegration of a larger body (usually a comet but occasionally an asteroid). Thus each shower recurs at the same time each year, and the meteors seem to radiate from a point (the radiant) corresponding to the direction from which the meteoroids approach the Earth.

Most meteors vaporise during their descent, but a few survive and strike the Earth and are called meteorites. Once a meteorite lands on South African territory it belongs to the State and is protected by the South African Heritage Resources Agency (SAHRA). Trading in South African meteorites is illegal, as per the National Heritage Resources Act (Act No. 25 of 1999). Consult the ASSA policy document on meteorites for further guidance, particularly if you think you may have found a meteorite.

A number of significant meteorite falls have been recorded in southern Africa. The world’s largest known meteorite is the Hoba Meteorite in Namibia. The most recent meteorite fall in southern Africa happened on 2002 July 21 at Thuathe near Maseru in Lesotho. The event was witnessed as a daytime fireball from Johannesburg and the Free State. At least 500 fragments were recovered with a total mass of about 30 kg. It is estimated that on entry the meteoroid weighed about a ton.