Comets Essay, Research Paper
Comets have been witnessed ever since man has been speculating about objects in the nighttime sky and appear in records from the beginning of recorded civilization (Schweighauser 20). Comets are made up of four distinct features. The first is the nucleus. The nucleus is made up of frozen gases, mostly water vapor with lesser amounts of carbon dioxide and carbon monoxide, and imbedded in the frozen gases are interplanetary dust and tiny fragments of stony and metallic meteoric material. Some comets, the larger ones, have a nucleus of 10 kilometers (Schweighauser 22). The second feature of comets is the coma. The coma is composed of atoms and molecules of gas that travels with the nucleus. The coma may be up to 100,000 kilometers in diameter. The third feature of a comet is the head. The head is just the name given to the coma and nucleus. The last of the features of the comet are the tails. Most comets have two tails. One tail is made from dust particles and the other, called ion tail, is made gases. As a comet approaches the sun, the frozen gas becomes unfrozen which causes the dust particles to become free. Light pressure from the sun and some other forces cause these materials to move away from the head of the comet and in the opposite direction from the sun. According to Charles A. Schweighauser in his book, entitled Astronomy from A to Z: A Dictionary of Celestial Objects and Ideas, he states that we see comet heads and tails because they not only reflect sunlight, but they also fluoresce give off their own light when comets are near the sun. The tails from the comet may be up to 150 million kilometers long each or together. Comets have a predictable orbit. There are one thousand comets that have been charted. Some comets go by the sun once and others, which are called periodic comets, pass the sun repeatedly following a predicable pattern. I have chosen a periodic comet called Tempel-Tuttle. Ernst Wilhelm Liebrecht Tempel and Horace Parnell Tuttle discovered this comet. This comet has been witnessed as early as 1366. The best apparition was that of 1366 when it passed 0.0229 AU from earth, making it the third closest approach of a comet to our planet in recorded history. ON the most recent apparition, the comet was recovered by the Keck II 10-m reflector at Mauna Kea by Karen J. Meech, O.R. Hainut, and J. Bauer on 1997 March 4. When they witnessed it, there was no trace of a coma, but by January the diameter of the coma was between 8 and 12 arc minutes. The comet passed closest to the sun on February 28,1998.