| HotLiquidMagma.com A Practical Guide to Astronomy |
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Comets |
| What Are They?
Comets sometimes called 'dirty snowballs' consist of rock and ice. Most comets travel in long, peculiar orbits through our Solor System. As they come close to the Sun, the comet's elements begin to melt (typically its ice turns to gas). This causes a tail to stream out from behind the comet. As of 1995, 878 comets have been cataloged and their orbits at least roughly calculated. Of these 184 are periodic comets (orbital periods less than 200 years). In nearly all cases, comets are named after their discoverer(s). |
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Image to Right: Comet Hale-Bopp taken from the campus of Lowell Observatory, Flagstaff Arizona. March 8, 1997. Used with permission. Copyright by Michael F. A'Hearn. |
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Unlike other small bodies in the solar system, comets have been known since antiquity. There are Chinese records of Comet Halley going back to at least 240 BC. For thousands of years, comets were seen as a sign from a god. When Halley's was spotted in 1066, William the Conqueror believed it was a sign that he would win the Battle of Hastings, and he did. Halley's will next appear in 2061. Until Hale-Bopp's spectacular appearance in early 1997 (pictured above), Halley's Comet was the most famous, appearing every 76 years, the last being 1986. It will next appear in mid 2061.
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| Image to Left: Comet Halley's Nucleus |
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