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comet

From The Hutchinson Unabridged Encyclopedia with Atlas and Weather Guide
Small, icy body orbiting the Sun, usually on a highly elliptical path that takes it beyond the dwarf planet Pluto. A comet consists of a central nucleus a few kilometres across and is made mostly of ice mixed with gas and dust. As a comet approaches the Sun its nucleus heats up, releasing gas and dust, which form a coma (comet head) up to 100,000 km/60,000 mi wide, around the nucleus. Gas and dust stream away from the coma to form one or more tails, which may extend for millions of kilometres. Some comets, such as Halley's Comet, stay within Pluto's orbit for most of the time. Comets are of many different types, characterized by their orbits, their composition (the ratio of ice to dust, and the amount of frozen volatiles other than water ice, such as methane and carbon monoxide), and their size. Most comets approach the Sun on a hyperbolic orbit and are seen only once; others (the periodic comets) return regularly in elliptical orbits. Famous examples of the periodic comets are…
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Full text Article comet tails

From Collins Dictionary of Astronomy
Tails of gas and dust that point in the antisolar direction away from the cometary nucleus and appear only when a comet is near the Sun, i.e. closer than about 2 AU (see illustration). Not all comets have tails. The luminosity is due to both molecular and atomic emission and to reflection of…
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Full text Article comet

From Collins Dictionary of Astronomy
A minor member of the Solar System that travels around the Sun in an orbit that generally is much more eccentric than the orbits of planets. Typical comets have three parts: the nucleus , coma , and comet tail . The gas and dust tails of a comet appear only when the comet is near the Sun and always…
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The cumulative inclination...
Abstract Comets are small icy bodies regarded as remnants of the time of planetary accretion when the Solar System was formed. The chapter discusses where comets originated, where they have spent most of their lives, and how they occasionally evolve through the planetary system and move close enough…
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Comet Hale-Bopp on April 8, 1997,...
Abstract Scientific understanding of comets has been accelerated by many recent missions to comets. The nuclei have sizes in the range 1-10km and their surfaces are very dark and diverse; interiors are likely loose agglomerations of smaller icy cometesimals and have a bulk density of ≈0.5g/cm 3 . …
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Full text Article Comets

From The Visual Guides: Understanding The Universe Full text Article THE SOLAR SYSTEM
Description Time Total Time A comet is a small, icy celestial body whose spectacular tail can be seen from Earth. 00:01 – 00:11 00:01:37 A comet's luminous plume is visible only when it approaches the Sun. 00:11 – 00:18 The comet's core, composed of dust and ice, heats up and begins to melt. 00:18 – …
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Full text Article comets

From Chambers Dictionary of the Unexplained
A comet is a type of heavenly body to which many interpretations and theories have attached throughout history. A comet is a body of rock and ice moving through space that periodically passes close to the earth on its eccentric orbit around the sun. In earlier times the appearance of a comet in the…
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A sungrazing comet imaged by the...
Comets were considered by many ancient civilisations as harbingers of doom, such as defeat in war or the death of a king. However, many philosophers tried to find more rational explanations. For example, the Pythagoreans (sixth and fifth centuries BC) and Hippocrates of Chios (c. 440 BC) believed…
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Full text Article comet

From The Columbia Encyclopedia
[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…
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Full text Article COMET

From Gaither's Dictionary of Scientific Quotations
…obviously, then, comet Kohoutek promises to be the celestial extravaganza of the century. A Comet for Christmas Newsweek, November 5, 1973 (p. 109 ). We have reason to know that many weak people have been alarmed, and many still weaker people made positively ill, by an announcement which has…
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Full text Article comet

From The Hutchinson Unabridged Encyclopedia with Atlas and Weather Guide
Small, icy body orbiting the Sun, usually on a highly elliptical path that takes it beyond the dwarf planet Pluto. A comet consists of a central nucleus a few kilometres across and is made mostly of ice mixed with gas and dust. As a comet approaches the Sun its nucleus heats up, releasing gas and…
| 936 words
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