METEOR<br /><ul><li> The term meteor comes from the Greek meteoron, meaning phenomenon in the sky. It is used to describe the streak of light produced as matter in the solar system falls into Earth's atmosphere creating temporary incandescence resulting from atmospheric friction. This typically occurs at heights of 80 to 110 kilometers (50 to 68 miles) above Earth's surface. The term is also used loosely with the word meteoroid referring to the particle itself without relation to the phenomena it produces when entering the Earth's atmosphere. A meteoroid is matter revolving around the sun or any object in interplanetary space that is too small to be called an asteroid or a comet. Even smaller particles are called micrometeoroids or cosmic dust grains, which includes any interstellar material that should happen to enter our solar system. A meteorite is a meteoroid that reaches the surface of the Earth without being completely vaporized. </li></li></ul><li><ul><li>Meteor streams that form as a result of commentary activity around perihelion consist of both structured and background components. The former are often referred to as trails. A trail is created at each perihelion passage as a result of the meteoroids' range of orbital periods. Trail locations can be precisely calculated by numerical integrations, allowing predictions of meteor outbursts and storms. The initial distribution of meteoroids, which relates to the meteor shower profile, depends on the meteoroid production rate and ejection velocity distribution as functions of heliocentric distance and on solar radiation pressure. The profile can gradually evolve owing to other irradiative forces. This paper reviews such work on these aspects of shower predictions.</li></li></ul><li>Meteorite<br /><ul><li>A naturally occurring solid object from interplanetary space that survives impact on a planetary surface. While in space, the object is called a meteoroid, and a meteor if it produces light or other visual effects as it passes through a planetary atmosphere. Explosive surface impacts by large meteorites are believed to have created the plethora of craters on the solid planets and moons of the solar system.</li></li></ul><li>Difference between meteors and meteorites<br /><ul><li>Meteoroids are either a small or a big object like a rock or metal that floats in space, usually found 'orbiting' on a belt. Meteors are meteoroids that have entered the Earth's atmosphere and are also called shooting stars. Meteorites are meteors that are not entirely burned and have landed on the Earth's surface.
Meteoroids are flying in space, meteors are falling through the atmosphere (thus "meteor" shower) and meteorite is a rock that's survived entry into the atmosphere.
Meteoroids are usually tiny loose dust particles from comets and asteroids. They become meteors, or shooting stars, once they enter the Earth's atmosphere, where friction from greenhouse gases forms a bright streak of light trailing behind the meteor. Most meteors burn up before reaching the Earth's surface, but those that don't end up hitting the Earth's crust, and are finally called meteorites.</li></li></ul><li> Hannover, 1995 Perseid Shower, 1996 Peekskill, 1992<br /> The left image shows the path of a fireball recorded over Hannover, Germany. The fireball outshines Sirius and the constellation Orion (Ref). The middle image shows a fireball recorded in the 1996 Perseid meteor shower by the Dutch Meteor Society. The curved streaks are star tracks in the timed exposure. The pulsed nature of the fireball track is produced by the camera which is being chopped. The right image shows a fireball observed for over 20 seconds from Kentucky to New York in 1992 that led to a meteorite fall in Peekskill, New York. In this image the fireball is beginning to break up into smaller pieces. Here is a movie of the Peekskill fireball (972 kB; Source). <br />
<ul><li>A meteor shower happens when a cluster of meteoroids orbiting the Sun cross the path of the Earth’s orbit. The meteoroids enter the Earth’s atmosphere at a similar time each year. Their path is also roughly the same; therefore they seem to radiate from a certain spot in the sky. So where do the meteoroids come from that cause meteor showers? Typically, comets that also orbit our Sun will have a trail of debris following them. This trail of debris is filled with meteoroids. A meteoroid is a small, stony or metallic object. Meteoroids are made up of materials similar to asteroids, but are much smaller. Asteroids and meteoroids are generally made up of minerals such as quartz or ferrous metals like iron and/or nickel. They can be as small as a grain of sand or dust particle or as large as the size of large boulders.</li></li></ul><li>The Leonid meteor shower<br />The Perseids meteor<br />Meteor shower<br />
Asteroids<br /><ul><li>In 1992, the first of the trans-Neptunian “asteroids” was discovered. Called Kuiper Belt objects (KBOs), about 900 had been found by mid-2004. They represent a population of bodies much more numerous than the main-belt or Trojan asteroids, but are more properly thought of as comets. There are also a modest number of minor planets orbiting the Sun in temporary orbits beyond Jupiter but well inside the KuiperBelt; they are termed Centaurs.
Most asteroid orbits are more elliptical and inclined to the plane of the ecliptic than the orbits of major planets. A number of small asteroids (Amor objects) cross, but do not intersect, the orbit of Mars, and a few even cross the Earth's orbit (Apollo objects) or orbit inside the Earth's orbit (Aten objects).
One of the many thousands of small planets (minor planets) revolving around the Sun, mainly between the orbits of Mars and Jupiter. Newly discovered asteroids are assigned a catalog number and name (such as 433 Eros) only after they are observed often enough to compute an accurate orbit. There are over 73,000 cataloged asteroids.</li></li></ul><li><ul><li> Described as "minor planets," asteroids are rocky objects that orbit around the Sun; most of them are located in a belt between Mars and Jupiter. Scientists believe there may be more than 50,000 asteroids in that belt, and perhaps millions more elsewhere in space. They range in size from nearly 600 miles (965 kilometers) in diameter to some that are only about 20 feet (6 meters) across. (While 20 feet seems small compared to 600 miles, the smallest asteroids would still have a pretty impressive impact if they hit Earth.) </li></li></ul><li>Distribution in the solar system<br />The average chemical and isotopic composition of the solar system is appropriately referred to as cosmic, since this elemental abundance distribution is found to be nearly the same for interstellar gas and for young stars associated with gas and dust in the spiral arms of galaxies. <br /><ul><li>The Sun makes up more than 99.9% of the mass of the solar system, so the bulk chemical composition of the solar system is essentially the same as that of the Sun. The cosmic abundances of the nonvolatile elements are determined from chemical analyses of a type of meteorite known as CI chondrites, whereas the relative abundances of the volatile elements are determined from quantitative measurements of the intensities of elemental emission lines from the Sun's photosphere.
In most silicate-rich meteorites and the Earth, Moon, Venus, and Mars, the most abundant elements are oxygen, magnesium, silicon, iron, aluminum, and calcium. Average solar-system composition consists of 70.7 wt % hydrogen, 27.4 wt % helium, and only 1.9 wt % of all remaining elements, lithium to uranium. Cosmic abundances are now widely referred to as standard abundances in the astrophysical literature.</li></li></ul><li><ul><li> 1758 German physician and astronomer Heinrich Wilhelm Matthäus Olbers was born in Abergen. He is famous for studying the asteroid belt and for discovering and naming several individual asteroids and comets.</li></li></ul><li> 1801 - Asteroid Ceres discovered.<br />The first asteroid was discovered by Italian astronomer Giuseppe Piazzi. He named his discovery Ceres after the Roman goddess of the harvest and motherly love. The asteroid was discovered to conform with the Titus-Bode law that suggested a planet should appear between the orbits of Mars and Jupiter. It is the largest body in the asteroid belt that was discovered soon after.<br />
Comets<br />One of the major types of objects that move in closed orbits around the Sun. Compared to the orbits of planets and asteroids, comet orbits are more eccentric and have a much greater range of inclinations to the ecliptic (the plane of the Earth's orbit). Physically, a comet is a small, solid body which is roughly 2 mi (3 km) in diameter, contains a high fraction of icy substances, and shows a complex morphology, often including the production of an extensive atmosphere and tail, as it approaches the Sun.<br />
Why do comets have tails?<br />Gas and dust are forced away from them by solar wind.<br />Any of a class of small icy objects orbiting the Sun and developing diffuse gaseous envelopes and often long glowing tails when near the Sun. They are distinguished from other objects in the solar system by their composition, hazy appearance, and elongated orbits. Most comets originate in the Oort cloud or in the Kuiper belt. Other bodies' gravity can alter their orbits, causing them to pass close to the Sun. Short-period comets return in 200 years or less, others in thousands of years or not at all. A comet typically consists of a small, irregular nucleus, often described as a "dirty snowball," with dust and other materials frozen in water mixed with volatile compounds. When one nears the Sun, the heat vaporizes its surface, releasing gases and dust particles, which form a cloud (coma) around the nucleus. Material in the coma may be pushed away from the Sun by its radiation and the solar wind, forming one or more tails. Meteor showers occur when Earth passes through dust left by the passage of a comet.<br />
Composition of comets<br />Comets may be composed of many different things depending on their origins, but many contain large quantities of ice. Of the other contents, there may be metals such as iron, iridium, and other minerals. Trapped in the ice, moreover, there may be samples of gasses, if the comet came from some planetary form or if it passed through a gaseous cloud. The tail of the comet is simply a stream of evaporating water and gasses from its surface. <br />
<br /><ul><li> On July 23, 1995, an unusually large and bright comet was seen outside of Jupiter's orbit by Alan Hale of New Mexico and Thomas Bopp of Arizona. Careful analysis of Hubble Space Telescope images suggested that its intense brightness was due to its exceptionally large size. While the nuclei of most comets are about 1.6 to 3.2 km (1 to 2 miles) across, Hale-Bopp's was estimated to be 40 km (25 miles) across. It was visible even through bright city skies, and may have been the most viewed comet in recorded history. Comet Hale-Bopp holds the record for the longest period of naked-eye visibility: an astonishing 19 months. It will not appear again for another 2,400 years.</li></ul> <br />Alan Hale<br />Thomas Bopp <br />COMET HALE-BOPP<br />
February 29, 1820 – January 5, 1913<br /><ul><li>Lewis Swift was an American astronomer. He discovered or co-discovered a number of comets, including periodic comets 11P/Tempel-Swift-LINEAR, 64P/Swift-Gehrels, and 109P/Swift-Tuttle (parent body of the Perseids meteor shower). He also discovered comet D/1895 Q1 (a.k.a. D/Swift) whose debris stream Mariner 4 probably encountered on September 15, 1967. Note, however, comet 54P/de Vico-Swift-NEAT was discovered by his son Edward D. Swift rather than by him. Apart from comets, he also discovered hundreds of nebulae.</li></ul>COMET SWIFT-TUTTLE 1992<br />
Historical occurrence of different comets<br /><ul><li>Though frequently beautiful, comets traditionally have stricken terror as often as they have generated wonder as they arc across the sky during their passages around the Sun. Astrologers interpreted the sudden appearances of the glowing visitors as ill omens presaging famine, flood or the death of kings. Even as recently as the 1910 appearance of Halley's Comet, entrepreneurs did a brisk business selling gas masks to people who feared Earth's passage through the comet's tail. In the 4th century B.C., the Greek philosopher Aristotle concluded that comets were some kind of emission from Earth that rose into the sky. The heavens, he maintained, were perfect and orderly; a phenomenon as unexpected and erratic as a comet surely could not be part of the celestial vault. In 1577, Danish astronomer Tycho Brahe carefully examined the positions of a comet and the Moon against the star background Using observations of the comet made at the same time from two different locations, Tycho noted that both observers saw the comet nearly in the same location with respect to the background stars. If the comet was closer than the moon, this would not have been the case. This so-called parallax effect can be demonstrated if you hold up a finger and look at it while closing one eye and then the other. Tycho concluded that the comet was at least six times farther away than the moon. </li></li></ul><li> THE END<br />