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. If you have seen a fireball, please report your sighting. 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 vaporize 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 (Act 25 of 1999) and is protected by the South African Heritage Resources Agency. Trading in South African meteorites is illegal.
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.
Recommendations for meteor showers to observe during the year appear in the Sky Guide.
Download a comprehensive observing tutorial by Tim Cooper, “How To Observe Meteors“, as published in MNASSA (2007 June, 113-118).
Recent articles published in mnassa
- Southern African Fireball Observations 2011 – 2012 (T.P. Cooper)
- The Daytime Bolide of 12 March 2013 (T.P. Cooper)
- The 2013 Eta Aquariids from Bredell (T.P. Cooper)
- Fireball and Bolide Observations; 2009-2010 (T.P. Cooper)
- Spectacular meteor over the Northern Province (Magda Streicher)
- Southern African Fireball Observations 2007/8 (T.P. Cooper)
- The History of the Hoba Meteorite: Part I: Nature and Discovery (P.E. Spargo)
- The History of the Hoba Meteorite: Part II: The News Spreads… (P.E. Spargo)
- The History of the Hoba Meteorite: Part III: Known and loved by all … (P.E. Spargo)
- Southern African Fireball Observations 2006 (T.P. Cooper)
- A probable spectacular bolide observed on 3 May 2007 (T.P. Cooper)
- Southern African Fireball Observations 2005 (T.P. Cooper)
- Visiting the Hoba Meteorite (Ian Glass)