Introductioncomet [Gr., = longhaired], a small celestial body consisting mostly of dust and gases that moves in an elongated elliptical or nearly parabolic orbit around the sun or another star. Comets visible from the earth can be seen for periods ranging from a few days to several months. They were long regarded with awe and even terror and were often taken as omens of unfavorable events. In 1987 a comet orbiting the star Beta Pictoris was identified, and since then an increasing number of exocomets have been found.
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