Wednesday, April 29, 2009

Meteors, Meteoroids, and Meteorites


Meteors are commonly called shooting stars, although they have nothing to do with stars at all. A meteor is a streak of light in the sky resulting from the ionization of a narrow channel in the Earth’s upper atmosphere. The heat generated by friction with air molecules ionizes a pathway behind the piece of debris.
While smaller meteoroids (often called micrometeoroids) are typically the rocky fragments left over from a broken-up comet, the meteor phenomenon is very different from a comet. A meteor sighting is a momentary event. The meteor streaks across a part of the sky. As we have seen, a comet does not streak rapidly and may, in fact, be visible for many months because of its great distance from the earth. A meteor is an atmospheric event, whereas a comet is typically many A.U. distant from the earth.
Meteor is the term for the sight of the streak of light caused by a meteoroid—which is the term for the actual rocky object that enters the atmosphere. Most meteoroids are completely burned up in our atmosphere, but a few do get through to strike the earth. Any fragments recovered are called meteorites.
While most of the meteors we see are caused by small meteoroids associated with comet fragments (about the size of a pea), larger meteoroids, more than an inch or so, are probably asteroid fragments that have strayed from their orbit in the asteroid belt. Such fragments enter the earth’s atmosphere at supersonic speeds of several miles per second and often generate sonic booms. If you see a very bright meteor—the brightness of the planet Venus or even brighter—it is one of these so-called fireballs. It is estimated that about 100 tons of meteoric material fall on the earth each day.

1 comment:

annalmae said...

Can anyone help me identify what this was?Friday 30th May, Republic of Ireland, around 11pm, while only the brightest stars were showing, in a light sky uninterrupted by town light we looked up and saw a large,bright "Shooting star" travel quickly but for a good couple of seconds the breadth of the sky. I got excited thinking it must have been big as few stars were showing...Would it have been a "fireball", a larger meteor burning a trail through the atmosphere as you describe? Is it a common occurence? It felt very magical to us... thankyou!