A meteor is a bright streak of light in the sky (a “shooting star” or a “falling star”) produced by the entry of a small meteoroid into the Earth’s atmosphere. If you have a dark clear sky you will probably see a few per hour on an average night; during one of the annual meteor showers you may see as many as 100/hour. Very bright meteors are known as fireballs.
A meteorite is a meteor that survives an impact with the Earth’s surface. While it’s still out in space it is called a meteoroid. When it enters the atmosphere, impact pressure causes the meteoroid to heat up and emit light, thus forming a meteor or fireball. The term bolide refers to either an extraterrestrial body that collides with the Earth, or to an exceptionally bright, fireball-like meteor regardless of whether it ultimately impacts the surface or not.
More generally, a meteorite on the surface of any celestial body is a natural object that has come from elsewhere in space. Meteorites have been found on the Moon and Mars.
Meteorites that are recovered after being observed as they came through the atmosphere or impacted the Earth are called falls. All other meteorites are known as finds. As of mid-2006, there are approximately 1,050 witnessed falls having specimens in the world’s collections. In contrast, there are over 31,000 well-documented meteorite finds.
Meteorites are always named for the place where they were found, usually a nearby town or geographic feature. One notable exception is Barringer Crater (commonly referred to as Meteor Crater) in Arizona which is named after the man who posited that it was formed in an impact with an extraterrestrial object. In cases where many meteorites were found in one place, the name may be followed by a number or letter (e.g., Allan Hills 84001 or Dimmitt (b)). Some meteorites have informal nicknames: the Sylacauga meteorite is sometimes called the “Hodges meteorite” after Ann Hodges, the woman who was struck by it; the Canyon Diablo meteorite, which formed Meteor Crater has dozens of these aliases. However, the single, official name designated by the Meteoritical Society is used by scientists, catalogers, and most collectors.
Meteorites have traditionally been divided into three broad categories: stony meteorites are rocks, mainly composed of silicate minerals; iron meteorites are largely composed of metallic iron-nickel; and, stony-iron meteorites contain large amounts of both metallic and rocky material. Modern classification schemes divide meteorites into groups according to their structure, chemical and isotopic composition and mineralogy.
Most meteoroids disintegrate when entering Earth’s atmosphere. However, an estimated 500 meteorites ranging in size from marbles to basketballs or larger do reach the surface each year; only 5 or 6 of these are typically recovered and made known to scientists. Few meteorites are large enough to create large impact craters. Instead, they typically arrive at the surface at their terminal velocity and, at most, create a small pit. Even so, falling meteorites have reportedly caused damage to property, livestock and people.
One of the primary goals of studying meteorites is to determine the history and origin of their parent bodies. Several meteorites recovered from Antarctica since 1981 have conclusively been shown to have originated from the moon based on compositional matches of lunar rocks obtained by the Apollo missions of 1969-1972. Sources of other specific meteorites remain unproven, although another set of eight meteorites are suspected to have come from Mars. These meteorites contain trapped atmospheric gases which match the composition of the Martian atmosphere as measured by the Viking landers in 1976. All other groups are presumed to have originated on asteroids or comets; the majority of meteorites are believed to be fragments of asteroids.
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The meteor shower peak is expected to be Thursday night-Friday morning this week around midnight to 2am. The entire northern hemisphere can see it best if you get away from the city lights to a darker sky location. If you stay in the city you will only be able to see the bigger and brighter ones.
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This is a calendar for all of the predicted meteor showers for the whole year. It is the International Meteor Organization. Enjoy.
http://www.imo.net/calendar/2010
1) Meteors can be very _bright_, but not necessarily large. Don’t confuse brightness and size; they are two totally different things!
2) Bright fireballs occur everywhere in the world every day. They occur high in the upper atmosphere and hence are visible over a large area. Most people get the impression that the fireball must have landed “just over the hill” but usually it is quite far away. I saw a bright fireball a few months ago which actually landed about 200 km away from where I observed it.
3) There is no satellite coverage which would pick up an event like this. While extremely bright from your point of view, it would be just a tiny speck from space. Meteor falls are located by comparing observer’s reports over a wide area and triangulating. That’s how the meteor I observed was located. Here in southern Ontario we have a network of ground-based all-sky cameras which enable scientists to pinpoint meteor falls accurately, but such a network doesn’t exist most places.
http://aquarid.physics.uwo.ca/all_sky.htm
“A very small object will be attenuated very sharply by the earth’s atmosphere, so will strike the ground with a low velocity. As the mass increases less speed will be lost. Does anyone have a ballpark figure for the kind of mass necessary to allow impact speeds to be close to the original speed?”
Actually, it doesn't turn out that way. The key parameter determining deceleration is the ballistic coefficient, which is related to the mass per unit area of the approaching object (and also to the drag coefficient, but we will take that as a constant across all spheroidal objects). For a constant density, mass increases with the cube of the diameter but frontal area increases with the square of the diameter. This means that larger objects will have larger ballistic coefficients and will decelerate less. And faster objects (say 70 km/sec) will have so much kinetic energy, that the relative deceleration may be minor. But you have to work out the numbers.
An excellent scale example is the Barringer Meteor Crater in Arizona which was characterized as being comprable to a 5-10 megaton nuclear surface detonation. The impact object is estimated to have been 50 meters in diameter.