By Gladstone C. Walling, Contributor
PERHAPS LAST November you went out into the night to observe a most spectacular show of "Shooting Stars". Well, they were not shooting stars but meteors. It was predicted that this Leonid meteor shower "(was) the last such squall for generations to come".
First of all let me reinforce what was mentioned above, that is, the trail of light that moves very quickly across the sky, lasting only a second or two is not a "shooting star", or the glowing effect left by a "falling star". A star is an immense object. Our Sun is a star with a diameter of 1,392,000 km.
If these glowing phenomena streaking across the sky are not "falling stars" or "shooting stars" they must be relatively small objects compared to the size of Earth and so they are.
Research has shown that on average some 150,000 to 200,000 tonnes of dust and rock from the space bombard the Earth's atmosphere each year; among this cascade of debris, meteoroids are to be found. The meteoroids enter earth's atmosphere at a speed of about 40 km per second and the brightening phase takes place at about 75 to 120 km above the Earth's surface.
This material has large variations in size and composition. The smallest member of this family is the meteoroid that starts at a size much smaller than a tiny pebble. As the meteoroid enters the earth's atmosphere it "rubs" against the molecules of the Earth's atmosphere which causes friction between itself and the air molecules. The heat generated by the friction excites the air molecules causing them to emit light as the electrons return to their ground states, producing the characteristic bright streak of light that is called a meteor.
Some meteoroids are of such a size that they will not be totally consumed in the burning phase and therefore survive the trip through the atmosphere to strike the earth's surface. The material that arrives at the surface of the earth is known as a meteorite. Before striking the earth's surface, the phenomena reveals itself as a long extremely bright trail of light with a large frontal lobe or fireball, some times accompanied by a sonic boom due to the supersonic speed with which it travels through the earth's atmosphere.
The impact of an extremely large meteorite on land or sea would dramatically change the climatic conditions on Earth. There is evidence to indicate that such an event took place some 65 million years ago and formed the 200km Chicxulub Crater on the Yucatan Peninsular, the aftermath of which was the extinction of a large number of plant an animal species including the dinosaurs.
Most of the meteoroids come from the dust and rocks left behind by comets that sublimate in their path around the Sun, debris from the collision of asteroids, ejected debris from impact mechanisms on the Moon and on Mars and a smaller quantity from general space dust and debris.
Periodically the Earth in its orbit around the sun can pass through a trail of dust and debris left behind by a Comet. When the dust enters the earth's atmosphere, to the observer on earth, all the meteors in a shower seem to originate from the same point known as the radiant. For example the Leonid meteors that was observed from Jamaica in last November appeared to "come out of" or radiate from the Constellation Leo.
Modern records go back as far as 1799 when it was said that the meteors "were as numerous as the stars". The grandeur of the shower was reported from America and Europe and from the Caribbean by Alexander von Humbolt's account of the great meteor shower.
Gladstone C. Walling, president, Astronomical Association of Jamaica; member, Council of the Jamaica Association of Scientists & Technologists.
