Many – perhaps most – of the meteors that hit Earth are associated with certain comets. Some of these periodic comets can still be seen; others have long since fallen apart, and only left a trail of dust. A given comet’s dust particles roughly maintain their parent’s orbit, they continue to move through space together, but spread out over orbit with time. When the earth passes through this type of dust stream as it orbits the sun, we will see a sudden explosion of meteorite activity, which usually lasts for several hours; such an event is called a meteor shower.
The dust particles & pebbles that produce the meteor shower travel together in space before hitting the earth. Therefore, when we observe the atmosphere, its parallel orbit seems to come to us from a place in the sky called radiant. This is the direction in which the meteor shower seems to diverge in space, just as long railroad tracks seem to deviate from a point on the horizon.
Meteor showers are often named after the constellation in which this radiant is located: The Perseid meteor shower, for example, has its radiant in the constellation Perseus. But you will likely see meteor showers any-where the sky, not just in the Radiant constellation. The characteristics of some of the most famous meteor showers.
|Shower Name||Date Of Maximum||Associated Parent Object||Comet’s Period (Years)|
|Quadrantid||Jan 3-4||2003EH (asteroid)||–|
|Lyrid||April 22||Comet Thatcher||415|
|Eta Aquarid||May 4-5||Comet Halley||76|
|Delta Aquarid||July 29-30||Comet Machholz||–|
|Perseid||Aug 11-12||Comet Swift Tuttle||133|
|Orionid||Oct 20-21||Comet Halley||76|
|Southern Taurid||Oct 31||Comet Encke||3|
|Leonid||Nov 16-17||Comet Tempel Tuttle||33|
|Geminid||Dec 13||Phaethon (asteroid)||1.4|
Meteorite dust is not always evenly distributed over the comet’s orbit, so for some years more meteors can be seen when the dust stream crosses the earth and less in other years. For example, A tightly packed distribution is associated with the Leonid meteors, which in 1833 and again in 1866 (after a 33-year interval, the cometary period) yielded the most spectacular showers (sometimes called meteor storms) ever recorded. During the Leonid Storm of November 17, 1866, up to 100 meteors per second were observed in some locations. The 2001 Leonid shower wasn’t as intense, but it peaked at nearly a thousand meteors per hour, one every few seconds, that could be observed from any. dark viewing place.
The most reliable annual meteorite display is the Perseid shower, which occurs around August 11th for about three nights each year. In the absence of bright moonlight, you can see a meteor every few minutes during a typical Persian shower. Astronomers estimate that the total mass of particles in the Persid Swarm is almost a billion tons; the comet that gave rise to-particles in this swarm, called Swift Tuttle, must originally have had at least as much mass. However, if its initial mass were comparable to mass measured for Halley’s Comet, SwiftTuttle would have contained several hundred billion tons, suggesting that only a very small fraction of the original cometary material survives in the meteor shower.
No meteor-showwer has ever survived its flight through the atmosphere & recovered for laboratory analysis. However, there are other ways to study the nature of these particles and thus gain additional information about the comets from which they are derived. Analysis of the trajectories of meteors shows that most of them are very light or porous, with densities typically less than 1.0g/cm3. If you place a fist-sized piece of meteor material on a table in the gravity of the earth, it might as well collapse under its own weight.
These light particles are easily destroyed in the atmosphere, which explains why relatively large meteors Shower cannot reach the earth. Comet dust is apparently fluffy, Very trivial stuff.. NASA’s Stardust mission used a special substance called aerogel to collect these particles. We can also deduce this from tiny comet particles that were recovered from high flying aircraft in the earth’s atmosphere. By nature, this fluff cannot reach the surface of the earth intact; however, more sub-stantial fragments of asteroids introduce it into our laboratories.