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Transcript
Other Celestial Objects Comets, asteroids, meteoroids, meteors, and meteorites Comet A comet is sometimes called a “dirty snowball”. It is a mixture of frozen water, gases and dust. A comet is invisible except when it is near the Sun. A comet has a very eccentric orbit. A comet’s tail As it approaches the Sun, a tail, millions of km long becomes visible. A comet’s tail will always face away from the Sun as it is created by the solar wind from the Sun. http://www.windows.ucar.edu /tour/link=/comets/comet_mo del_interactive.html http://www.esa.int/SPECIAL S/Rosetta/SEM3NV0PGQD_ 0.html asteroids Most asteroids are found in the asteroid belt, between Mars and Jupiter. They have a rocky composition. The largest asteroid known is Ceres Meteoroid A meteroid is a rock travelling through space but has yet to reach the Earth’s atmosphere. meteors A meteor is a bright streak of light in the sky (a shooting star or a falling star) produced when a small meteroroid enters the Earth’s atmosphere. Most meteoroids are small and burn up due to the heat of friction through the atmosphere. A Meteor’s orbit If you have a dark clear sky ,on an average night, you will probably see a few meteors per hour. During one of the annual meteor showers you may see as many as 100/hour. meteorites Only the largest meteors can survive travelling through Earth’s atmosphere and fall to Earth as meteorites. A Famous Meteorite The Hoba meteorite is the largest meteorite to be discovered. It was found in Namibia, Africa This meteorite weighs 60 tons. Meteorite craters Only meteoroids larger than a few hundred tons can survive and hit Earth, leaving a crater. This crater is the Barringer Crater, near Winslow,Arizona. It was formed 50,000 years ago by an iron meteor about 30-50 m in diameter. The crater is 1200 m in diameter and 200 m deep. About 120 impact craters have been identified on the Earth.