Barrett,
So is the "Asteroid Belt" actually;
a "Meteriod Belt", an "Asteriod Belt", or a "Satellite Belt" ? ;~}
Jonathan
----- Original Message -----
From: "Barrett" <[email protected]>
To: <[email protected]>
Sent: Saturday, January 15, 2011 5:29 PM
Subject: [meteorite-list] Meteorites 101
The definitive source WIKIPEDIA!! Says;
MeteoroidThe current official definition of a meteoroid from the
International Astronomical Union is "a solid object moving in
interplanetary space, of a size considerably smaller than an asteroid and
considerably larger than an atom".[1][2] Beech and Steel, writing in
Quarterly Journal of the Royal Astronomical Society, proposed a new
definition where a meteoroid is between 100 µm and 10 m across.[3] The NEO
definition includes larger objects, up to 50 m in diameter, in this
category. Very small meteoroids are known as micrometeoroids (see also
interplanetary dust).
The composition of meteoroids can be determined as they pass through
Earth's atmosphere from their trajectories and the light spectra of the
resulting meteor. Their effects on radio signals also give information,
especially useful for daytime meteors which are otherwise very difficult
to observe. From these trajectory measurements, meteoroids have been found
to have many different orbits, some clustering in streams (see Meteor
showers) often associated with a parent comet, others apparently sporadic.
Debris from meteoroid streams may eventually be scattered into other
orbits. The light spectra, combined with trajectory and light curve
measurements, have yielded various compositions and densities, ranging
from fragile snowball-like objects with density about a quarter that of
ice,[4] to nickel-iron rich dense rocks.
Meteoroids travel around the Sun in a variety of orbits and at various
velocities. The fastest ones move at about 26 miles per second (42
kilometers per second) through space in the vicinity of Earth's orbit. The
Earth travels at about 18 miles per second (29 kilometers per second).
Thus, when meteoroids meet the Earth's atmosphere head-on (which would
only occur if the meteors were in a retrograde orbit), the combined speed
may reach about 44 miles per second (71 kilometers per second).
Meteor"Meteor" and "Meteors" redirect here. For other uses, see Meteor
(disambiguation).
See also Hydrometeor.
Comet 17P/Holmes and GeminidA meteor is the visible path of a meteoroid
that has entered the Earth's atmosphere. Meteors typically occur in the
mesosphere, and most range in altitude from 75 km to 100 km.[5] 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 in the direction of roughly
west at noon.[clarification needed] Most meteors are, however, observed at
night as low light conditions allow fainter meteors to be observed.
For bodies with a size scale larger than the atmospheric mean free path
(10 cm to several metres)[clarification needed] the visibility is due to
the atmospheric ram pressure (not friction) 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 (for example The Great Daylight 1972
Fireball).
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.[6]
FireballA fireball is a brighter-than-usual meteor. The International
Astronomical Union defines a fireball as "a meteor brighter than any of
the planets" (magnitude -4 or greater).[7] The International Meteor
Organization (an amateur organization that studies meteors) has a more
rigid definition. It defines a fireball as a meteor that would have a
magnitude of -3 or brighter if seen at zenith. This definition corrects
for the greater distance between an observer and a meteor near the
horizon. For example, a meteor of magnitude -1 at 5 degrees above the
horizon would be classified as a fireball because if the observer had been
directly below the meteor it would have appeared as magnitude -6.[8]
Bolide
An especially bright meteor, a bolide (in astronomy)"Bolide" redirects
here. For the Swedish guided missile BOLIDE, see RBS 70.
In astronomy
The word bolide comes from the Greek βολίς (bolis) which can mean a
missile or to flash. The IAU has no official definition of "bolide", and
generally considers the term synonymous with "fireball". The bolide term
is generally used for fireballs reaching magnitude -14 or brighter.[9]
Astronomers tend to use the term to mean an exceptionally bright fireball,
particularly one that explodes (sometimes called a detonating fireball).
In geology
Geologists use the term "bolide" more often than astronomers do: in
geology it indicates a very large impactor. For example, the USGS uses the
term to mean a generic large crater-forming projectile "to imply that we
do not know the precise nature of the impacting body ... whether it is a
rocky or metallic asteroid, or an icy comet, for example".[10]
SuperbolideIf the magnitude of a bolide reaches -17 or brighter it is
known as a superbolide.[9][11]
MeteoriteMain article: meteorite
A meteorite is a portion of a meteoroid or asteroid that survives its
passage through the atmosphere and impact with the ground without being
destroyed.[12] Meteorites are sometimes, but not always, found in
association with hypervelocity impact craters; during energetic
collisions, the entire impactor may be vaporized, leaving no meteorites.
TektiteMain article: tektite
Two tektitesMolten terrestrial material "splashed" from a meteorite impact
crater can cool and solidify into an object known as a tektite. These are
often mistaken for meteorites.
Meteoric dustMost meteoroids burn up when they enter the atmosphere. The
left-over debris is called meteoric dust or just meteor dust. Meteor dust
particles can persist in the atmosphere for up to several months. These
particles might affect climate, both by scattering electromagnetic
radiation and by catalyzing chemical reactions in the upper
atmosphere.[13]
Does this help any? Seems about correct.
-Barrett
-----Original Message-----
From: [email protected]
[mailto:[email protected]] On Behalf Of
[email protected]
Sent: Saturday, January 15, 2011 5:59 PM
To: [email protected]
Subject: Re: [meteorite-list] Meteorites 101
Bolide is a term that it's good to avoid. It doesn't mean anything... or
rather, it means too many different things. "Fireball" unambiguously
means
a
meteor of a specific apparent brightness. "Bolide" is simply confusing.<<
I usually think of a fireball as a meteor with a magnitude brighter than
-3. I also sometimes think of a Bolide as being a fireball that has
produced
a sonic boom as well.
GeoZay
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