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Astronomy: Meteors
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A meteoroid is the object floating in space before it comes in contact with the Earth and the Earth's atmosphere. A meteor is the object which flashes across the sky, most of the meteors burn up in our atmosphere. A meteorite is the remains of the object which flashed across the sky if it reaches Earth surface. If Earth crosses a comet trail the comet fragments will burn up in our atmosphere at an altitude of 80 kilometers. From the ground we see these meteors as jets of bright light, shooting across the sky. These tiny fragements (often only a few milimeters big) enter our skies at a speed of 10 kilometers per second. On every clear night you can see a few meteors per hour burn up in the atmosphere. And as Earth follows the same path around the Sun every year, it always crosses a comet trail at the same point in its orbit. At these periods we can see meteor showers with dozens of meteors per hour. A meteor shower originates from the same point in the sky (the radiant) and they are named after the constellation from which they appear. (For example Leonids always appear around the constellation of Leo). |
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Meteor showers
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 Picture of the Perseid meteor shower |
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MeteoritesEvery now and then a meteor reaches the Earth's surface, which causes an impact crater. Luckily we are guarded by the atmosphere; most incoming objects burn up. But when a meteorites impacts, the forces are gigantic.Arizona meteor crater, USAThe meteor crater in the state of Arizona was the first crater to be identified as an impact crater. Between 20.000 to 50.000 years ago a small asteroid or comet about 30 meters in diameter impacted the Earth and formed the crater.The crater measures 1.2 km in diameter and is one of the best preserved craters on Earth. Aorounga impact crater, ChadThis impact took place several hundred million years ago. Scars are still visible in the landscape of the Sahara Desert of northern Chad.The picture on the right measures 22 by 28 kilometers. The impact crater can been seen with a diameter of about 17 kilometers. The original crater was buried by sediments, which were then partially eroded to reveal the current ring-like appearance. The dark streaks are deposits of windblown sand that migrate along valleys cut by thousands of years of wind erosion. The dark band in the upper right of the image is a portion of a proposed second crater. Scientists are using radar images to investigate the possibility that Aorounga is one of a string of impact craters formed by multiple impacts. Yucatan Peninsula (Dino crater), MexicoThe remains of the Chicxulub crater have been filled in by limestone sediments. This crater has become the focus of intense study in recent years.The ring that cuts across the Yucatan Peninsula pictured in this space shuttle image is one of the very few pieces of surface evidence that survives from a cataclysmic day in Earth history. It is commonly believed by scientist that this impact is responsible or at least set in motion the conditions that led to the demise of the dinosaurs. Dinosaurs could be extinct by a global shift in environment, or in global fires and tsunami's when the 10 km meteorite hit Earth (compare this size to the 30 meter meteorite that caused a 1.2 km crater in Arizona). Scientists have drilled samples through the crater area and are now investigating the rock chemistry. They hope to get a better picture of what happened on that day 65 million years ago and discover more about the subsequent catastrophic environmental changes that killed off 70% of all living species. Related subjects>> Comets>> Official Arizona Flagstaff Meteor Crater internetsite |
 The 1.2 km wide Arizona impact crater  This Aorounga impact crater image with a diameter of 17 km was acquired on April 18 and 19, 1994, onboard the space shuttle Endeavour.  Radar image of the enormous impact crater of Chicxulub, Mexico. The diameter is an estimated 160 to 240 kilometers and was caused by a 10 km meteorite.  Artist impression of the area after impact.  Map of Yucatan, Mexico. In the right corner lies Cuba. |
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