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Comets whose aphelia are near a major planet's orbit are called its "family". [81] Such families are thought to arise from the planet capturing formerly long-period comets into shorter orbits. [82] At the shorter orbital period extreme, Encke's Comet has an orbit that does not reach the orbit of Jupiter, and is known as an Encke-type comet.
Little is known of what people thought about comets before Aristotle, who observed his eponymous comet, and most of what is known comes secondhand.From cuneiform astronomical tablets, and works by Aristotle, Diodorus Siculus, Seneca, and one attributed to Plutarch but now thought to be Aetius, it is observed that ancient philosophers divided themselves into two main camps.
Halley's Comet is the only known short-period comet that is consistently visible to the naked eye from Earth, [16] appearing every 72–80 years, [17] though with the majority of recorded apparations (25 of 30) occurring after 75–77 years.
These comets come from the Kuiper belt and scattered disk, beyond the orbit of Pluto, with possible origins in the Oort cloud for many. For comets with an orbital period of over 1000 years (semi-major axis greater than ~100 AU), see the List of near-parabolic comets.
Comets orbiting in this way still originate from the Solar System, however. Typically comets in the Oort Cloud are thought to have roughly circular orbits around the Sun, but their orbital velocity is so slow that they may easily be perturbed by passing stars and the galactic tide. Astronomers have been discovering weakly hyperbolic comets that ...
Periodic comets usually have elongated elliptical orbits, and usually return to the vicinity of the Sun after a number of decades. The official names of non-periodic comets begin with a "C"; the names of periodic comets begin with "P" or a number followed by "P". Comets that have been lost or disappeared have names with a "D". Comets whose ...
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The most famous sungrazers are the Kreutz Sungrazers, which all originate from one giant comet that broke up into many smaller comets during its first passage through the inner Solar System. An extremely bright comet seen by Aristotle and Ephorus in 371 BC is a possible candidate for this parent comet.