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The word comet derives from the Old English cometa from the Latin comēta or comētēs. That, in turn, is a romanization of the Greek κομήτης 'wearing long hair', and the Oxford English Dictionary notes that the term (ἀστὴρ) κομήτης already meant 'long-haired star, comet' in Greek.
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.
De systemate orbis cometici, deque admirandis coeli characteribus (transl.Of the systematics of the world of comets, and on the admirable objects of the sky) is a small tract on comets and other celestial objects by the Sicilian astronomer Giovanni Battista Hodierna published in 1654. [1]
Astronomers posed over the past decade that dark comets, or objects that resemble asteroids but move like comets, may exist. Now, scientists have found a total of 14 of them.
This unique spiral galaxy, which is situated 3.2 billion light-years from the Earth, has an extended stream of bright blue knots and diffuse wisps of young stars. [2] It rushes at 3.6 million km/h (1000km/s [2]) through the cluster Abell 2667 and therefore, like a comet, shows a tail, with a length of 600,000 light-years.
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 ...
The appearance is analogous to the tail of a comet that faces away from its star, but comets are solid bodies and much smaller in overall size and mass. Globules located far and close to the central star present different characteristics.
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.