Great Comets of the 20th and 21st Centuries At the end of this year, comet ISON may become extremely bright, visible to the naked eye, and if so, will go down as one of the great comets of 21st century. Comets have existed since the creation of the solar system. They originate either in the Kuiper Belt, which contains Pluto and other dwarf planets, or the Oort Cloud, far off toward the edge of our solar system. Comets that originate in the Kuiper Belt are periodic over short timespans, and as such are called short-period comets. They have elliptical orbits. Oort Cloud comets, on the other hand, are long-period comets if they have elliptical orbits. Some are not periodic at all; rather, they have parabolic or hyperbolic orbits that pass the sun only once and then return to the Oort Cloud for good. In the early 1900s, Halley’s comet reached naked eye visibility and set the standard for comets in the future, such as Arend-Roland, Mrkos, and Seki-Lines. The brightest comet of the century, however, was Ikeya-Seki, a sungrazing comet that reached magnitude -10 in 1965. In 1969, comet Bennett sported a 20-degree tail, making it one of the longest comets of the 20th century. Then came Kohoutek. Kohoutek was expected to become extremely bright and was blown out of proportion by the media, so when it fizzled and was barely visible at all, the public was disappointed. It taught astronomers and the media an important lesson, that comets are impossible to accurately predict since their brightness stems from the sun, which can just as easily destroy them. Comet West came the following year. It flared up to magnitude -1, much brighter than predicted. This stemmed from the fact that West broke into several pieces, all of which began to be blown apart by the sun. Unfortunately, West was missed by most of the general population because the media, and even those who knew about West ahead of time, still had the Kohoutek flub fresh in their minds. To miss a great comet would have been terrible even under normal circumstances. What actually happened made it even worse. After Comet West in 1975, there was what came to be called a “comet drought.” Even Halley’s, in 1986, put on a disappointing display, and is barely remembered by most. No more bright comets graced the skies until comet Hyakutake in 1995. Hyakutake took the prize for longest tail. With a 62-degree-long tail, it was one of the most impressive comets of the 20th century. In 1994, comet Shoemaker-Levy 9 crashed into Jupiter, leaving spots on its surface that were visible for months. Yet neither beat Halley’s in 1910. This was left to the great Hale-Bopp. Comet Hale-Bopp, passing by in 1997, is considered the best comet since the Great Comet of 1882. The 2000s began with a bang. In 2002, Ikeya-Zhang became bright enough to make a beautiful binocular spectacle. Macholz put on a small display in 2005, and in 2006, comet Schwassmann-Wachmann returned to the inner solar system broken apart, putting on an unusual display for northern hemisphere observers. Finally, in 2007, McNaught reached magnitude -6, making it the brightest since Ikeya-Seki in 1965. Later that year, comet Holmes reached the inner solar system, passing very close to earth and appearing virtually tailless. Earlier this year, comet PANSTARRS passed close to the sun, making a good evening-sky binocular target, and with luck, ISON will go down as one of the great comets of the 21st century.
Posted on: Mon, 08 Jul 2013 16:39:57 +0000
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