Meteorites: A southern African perspective, by Ronnie McKenzie

Meteorites: A southern African perspective, by Ronnie McKenzie. Random House Struik Nature. Cape Town, South Africa 2014. ISBN 9781775840985 / ISBN 978-1-77584-098-5

Meteorites: A southern African perspective, by Ronnie McKenzie. Random House Struik Nature. Cape Town, South Africa 2014. ISBN 9781775840985 / ISBN 978-1-77584-098-5

A meteor passing through the atmosphere, possibly without dropping in altitude at all. Photo: Meteorites. A southern African perspective.

A meteor passing through the atmosphere, possibly without dropping in altitude at all. Photo: Meteorites. A southern African perspective.

A meteor exploding high above Earth's surface, resulting in a large strewn field. Image from Ronnie McKenzie's guide Meteorites: A southern African perspective (ISBN 9781775840985 / ISBN 978-1-77584-098-5)

A meteor exploding high above Earth's surface, resulting in a large strewn field. Image from Ronnie McKenzie's guide Meteorites: A southern African perspective (ISBN 9781775840985 / ISBN 978-1-77584-098-5)

To observers on the ground, meteorites often appear to be travelling towards Earth and to land just over the horizon. This and many other phenomenons about this space travellers are unveiled and explained from a southern African perspective by Ronnie McKenzie.

Ronnie McKenzie  

Although they appear to be heading downwards, they may, in reality, be 120 km or more above the ground and passing over the horizon, possibly without dropping in altitude at all. Such meteors simply start to burn up, in many cases forming spectacular fireballs, but they do not explode or ever come close to landing on Earth. After a display lasting perhaps just a few seconds, they travel back out into space, never to be seen again. If a meteor does in fact hit the surface of the Earth or if it explodes above the surface, it creates a significant noise either from the impact itself or from the associated shock wave. In both cases, the noise from the sonic boom can be heard and/ or felt more than 100 km away. If the observer does not hear any noise at all, then the meteor has either not landed, or the point of impact is too far away, despite the mpression that it must have been just over the next hill. The size of the object and the angle at which it enters the atmosphere influence the length of time it takes to travel towards the surface of the Earth and whether it will reach the ground, or simply burn up completely. Initially the atmosphere offers relatively little resistance to meteors. However, as the air becomes denser lower down, it acts much like a concrete wall to foreign bodies travelling at speed - sometimes of between 10km/s and 70km/s. At such speeds, even the relatively slight resistance from the upper atmosphere some 120 km above the ground can be enough to cause meteors to break up and, in most cases, to burn up completely. In cases where a meteor explodes relatively high above the ground, the pieces fall to Earth under gravity, having lost much of their initial speed during the explosion. The debris does not normally form craters; the pieces tend to fall onto the ground below and will often break up or occasionally bury themselves if the ground is sandy or particularly soft. If the main explosion occurs high up in the atmosphere, the resulting strewn field may be large, although its size is no indication of the amount of material reaching the ground. If the meteor manages to get closer to the surface of the Earth before exploding, then the resulting strewn field is likely to be smaller than for a higher explosion. Once again, the size of the strewn field is not indicative of the amount of material reaching the surface. From most reports, it appears that the majority of meteors exploding before they reach the ground tend to break up somewhere between 30km and 10km above ground, although some notable falls are estimated to have exploded as low down as 4 km above ground. Occasionally a meteor will enter the atmosphere at a speed and in a direction that enables it to pass through the atmosphere and reach the Earth's surface without breaking up completely. [...]

This is an excerpt from the guide: Meteorites: A Southern African Perspective, by Ronnie McKenzie.

Title: Meteorites
Subtitle: A Southern African Perspective
Author: Ronnie McKenzie
Genre: Meteorite collecting
Publisher: Random House Struik
Imprint: Nature
Cape Town, South Africa 2014
ISBN 9781775840985 / ISBN 978-1-77584-098-5
Softcover, 15 x 21 cm, 120 pages, throughout colour photographs

McKenzie, Ronnie im Namibiana-Buchangebot

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