page_title: Great comet
section_title: Causes
hierarchical_section_title: Great comet / Causes
context_page_description: A great comet is a comet that becomes exceptionally bright. There is no official definition; often the term is attached to comets such as Halley's Comet, which during certain appearances are bright enough to be noticed by casual observers who are not looking for them, and become well known outside the astronomical community. Great comets are rare; on average, only one will appear in a decade. Although comets are officially named after their discoverers, great comets are sometimes also referred to by the year in which they appeared great, using the formulation "The Great Comet of ...", followed by the year.
context_section_description: The vast majority of comets are never bright enough to be seen by the naked eye, and generally pass through the inner Solar System unseen by anyone except astronomers. However, occasionally a comet may brighten to naked eye visibility, and even more rarely it may become as bright as or brighter than the brightest stars. The requirements for this to occur are: a large and active nucleus, a close approach to the Sun, and a close approach to the Earth. A comet fulfilling all three of these criteria will certainly be spectacular. Sometimes, a comet failing on one criterion will still be extremely impressive. For example, Comet Hale–Bopp had an exceptionally large and active nucleus, but did not approach the Sun very closely, yet it still became an extremely famous and well observed comet. Equally, Comet Hyakutake was a relatively small comet, but appeared bright because it passed extremely close to the Earth.
caption: The Great Comet of 1680 over Rotterdam as painted by Lieve Verschuier
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