Definitions
Meteoroid: A meteoroid is a sand-to-boulder sized particle of debris in the Solar System. The visible path of a meteoroid that enters Earth's (or another body's) atmosphere is called a meteor. If a meteoroid reaches the ground and survives impact, then it is called a meteorite.
Asteroid: Asteroids, sometimes called minor planets or planetoids, are small Solar System bodies in orbit around the Sun or planets, especially in the inner Solar System; they are smaller than planets but larger than meteoroids.
Meteorite: A meteoroid or a part of it that enters Earth's (or another body's) atmosphere and reaches the ground and survives impact.
Meteor: The visible streak of light that occurs when a meteoroid enters the Earth's atmosphere, known popularly as a shooting star or falling star.
Comet: A small solar system body bigger than a meteoroid that, when close enough to the Sun, exhibits a visible coma, and sometimes a tail, both because of the effects of solar radiation upon the comet's nucleus. Comet nuclei are themselves loose collections of ice, dust and small rocky particles.
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Basics
A meteor is the visible streak of light that occurs when a meteoroid enters the Earth's atmosphere. Meteors typically occur in the mesosphere, and most range in altitude from 75 km to 100 km.
Millions of meteors occur in the Earth's atmosphere every day. Most meteoroids that cause meteors are about the size of a pebble. They become visible between about 40 and 75 miles (65 and 120 kilometers) above the earth. They disintegrate at altitudes of 30 to 60 miles (50 to 95 kilometers). Meteors have roughly a fifty percent chance of a daylight (or near daylight) collision with the Earth as the Earth orbits. Most meteors are, however, observed at night as low light conditions allow fainter meteors to be observed.
Meteor visibility is due to the atmospheric ram pressure that heats the meteoroid so that it glows and creates a shining trail of gases and melted meteoroid particles. The gases include vaporized meteoroid material and atmospheric gases that heat up when the meteoroid passes through the atmosphere. Most meteors glow for about a second. A relatively small percentage of meteoroids hit the Earth's atmosphere and then pass out again: these are termed Earth-grazing fireballs.
Meteors may occur in showers, which arise when the Earth passes through a trail of debris left by a comet, or as "random" or "sporadic" meteors, not associated with a specific single cause. A number of specific meteors have been observed, largely by members of the public and largely by accident, but with enough detail that orbits of the incoming meteors or meteorites have been calculated. All of them came from orbits from the vicinity of the asteroid belt.
Topics of Interest
A meteor shower is a celestial event in which a number of meteors are observed to radiate from one point in the night sky. These meteors are caused by streams of cosmic debris called meteoroids entering Earth's atmosphere at extremely high speeds on parallel trajectories. Most meteors are smaller than a grain of sand, so almost all of them disintegrate and never hit the Earth's surface. Fragments that do survive impact with Earth's surface are called meteorites. Intense or unusual meteor showers are known as meteor outbursts and meteor storms, which may produce greater than 1,000 meteors an hour.
Meteor Crater is a meteorite impact crater located approximately 43 miles (69 km) east of Flagstaff, near Winslow in the northern Arizona desert of the United States. Because the US Department of the Interior Division of Names commonly recognizes names of natural features derived from the nearest post office, the feature acquired the name of "Meteor Crater" from the nearby post office named Meteor. The site was formerly known as the Canyon Diablo Crater, and scientists generally refer to it as Barringer Crater in honor of Daniel Barringer who was first to suggest that it was produced by meteorite impact. The crater is privately owned by the Barringer family via their Barringer Crater Company.
The Perseids is the name of a prolific meteor shower associated with the comet Swift-Tuttle. The Perseids are so-called because the point they appear to come from, called the radiant, lies in the constellation Perseus. The name derives in part from the word Perseides, a term found in Greek mythology referring to the descendants of Perseus. The stream of debris is called the Perseid cloud and stretches along the orbit of the comet Swift-Tuttle. The cloud consists of particles ejected by the comet as it travels on its 130-year orbit. Most of the dust in the cloud today is around a thousand years old. However, there is also a relatively young filament of dust in the stream that was pulled off the comet in 1862. The rate of meteors originating from this filament is much higher than for the older part of the stream.
The Leonids are a prolific meteor shower associated with the comet Tempel-Tuttle. The Leonids get their name from the location of their radiant in the constellation Leo: the meteors appear to stream from that point in the sky. The 2009 display peaking on November 17 may produce more than 500 meteors an hour.
Meteor burst communications, or MBC for short, is a radio propagation mode that exploits the ionized trails of meteors during atmospheric entry to establish brief communications paths between radio stations up to 2250 kilometres (1400 miles) apart. It is also referred to as meteor scatter communications in some documents.
Source: Wikipedia (All text is available under the terms of the GNU Free Documentation License and Creative Commons Attribution-ShareAlike License.)
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