Commission F1 has recently issued an explanatory text for the correct usage of fundamental terms related to meteor astronomy in scientific literature and among the general public. The definitions in meteoric astronomy adopted in 1961 by the Commission 22 have recently undergone an update by its direct successor: the IAU Commission F1 on Meteors, Meteorites and Interplanetary Dust. See also meteor.As the rapid evolution of our knowledge in the field of meteoric astronomy progresses, the more it requires constant updates to the fundamental terms, to satisfactorily match the current state of the field. Individual meteoroids in the mass range 10 –6 to 10 4 grams are fragile crumbly rocky dust particles with a composition similar to carbonaceous chondrite meteorites. The space density of meteoroids maximizes near the orbit of Mars and then falls off as 1/ r 1.5, where r is the distance from the Sun. In the main they move around the Sun in low-inclination direct orbits. Meteoroids are usually produced by the decay of short-period comets and the collisional fragmentation of asteroids. The majority of the mass of the meteoroid cloud around the Sun is made up of particles with individual masses between 10 –7 and 10 –3 gram. meteoroid ( mee -tee-ŏ-roid) The collective term applied to meteoritic material in the Solar System, usually replaced by the terms micrometeorite for particles with mass less than 10 –6 gram and meteorite for bodies with mass greater than about 10 5 grams. The Columbia Electronic Encyclopedia™ Copyright © 2022, Columbia University Press. Such meteor showers are named for the constellation from which they appear to originate. The frequency of meteors also increases when the earth passes through certain swarms of particles that intersect the earth's orbit. More meteors are visible after midnight because the earth's rotation has then positioned the observer's part of the earth in the direction of the earth's motion about the sun. A single observer under a dark sky can see an average of 5 to 10 meteors per hour more during a meteor shower. Although most meteoroids are quite small, and even though only a very small fraction of them reach the earth's surface, their large quantity accounts for several tons of matter falling on the earth each day. Other meteoroids, the carbonaceous chondrites, are stony with a large amount of carbon. Meteoroids are composed of stone, iron, or a mixture of stone and iron, with other metals present in very small proportions. In 2013 a considerably smaller meteor injured some 1,200 people in Chelyabinsk, Russia, when shock waves from its explosion high in the atmosphere shattered glass in many buildings. The brightest fireball ever recorded fell in the Tunguska Basin, Siberia, in 1908, causing the destruction of forest over an area of about 770 sq mi (2,000 sq km). (Some dust-sized particles are so small and light, however, that they float down through the atmosphere without heating up due to friction.) A meteor of considerable duration and brightness is known as a fireball a fireball that breaks apart with an explosion is a bolide. They experience friction due to collisions with the atmosphere by the time they reach 50 to 75 mi (80–120 km) from the earth's surface, they have been heated to incandescence through friction and are visible as “shooting stars,” or “falling stars.” Most meteors disintegrate completely before they reach the earth those large enough to reach the ground are called meteorites. Perhaps a billion meteoroids a day enter the atmosphere, their speeds ranging from 10 to 45 mi (16–72 km) per sec. Countless meteoroids of varying sizes are moving about the solar system at any time. While still outside the atmosphere, the particle is known as a meteoroid. Meteor, appearance of a small particle flying through space that interacts with the earth's upper atmosphere.
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