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A comet is an icy, small Solar System body that warms and begins to release gases when passing close to the Sun, a process called outgassing.This produces an extended, gravitationally unbound atmosphere or coma surrounding the nucleus, and sometimes a tail of gas and dust gas blown out from the coma.
Stardust's discovery of crystalline silicates in the dust of comet Wild 2 implies that the dust formed above glass temperature (> 1000 K) in the inner disk region around a hot young star, and was radially mixed in the solar nebula from the inner regions a larger distance from the star or the dust particle condensed in the outflow of evolved red ...
A-type star In the Harvard spectral classification system, a class of main-sequence star having spectra dominated by Balmer absorption lines of hydrogen. Stars of spectral class A are typically blue-white or white in color, measure between 1.4 and 2.1 times the mass of the Sun, and have surface temperatures of 7,600–10,000 kelvin.
Comet orbits had been determined quite precisely, yet comets were at times recovered "off-schedule," by as much as days. Early comets could be explained by a "resisting medium"—such as "the aether", or the cumulative action of meteoroids against the front of the comet(s). [citation needed] But comets could return both early and late. Whipple ...
As the comet warms, parts of it sublimate; [1] this gives a comet a diffuse appearance when viewed through telescopes and distinguishes it from stars. The word coma comes from the Greek κόμη (kómē), which means "hair" and is the origin of the word comet itself. [2] [3] The coma is generally made of ice and comet dust. [1]
Common targets of amateur astronomers include the Sun, the Moon, planets, stars, comets, meteor showers, and a variety of deep-sky objects such as star clusters, galaxies, and nebulae. Astronomy clubs are located throughout the world and many have programs to help their members set up and complete observational programs including those to ...
A multiple star system consists of two or more stars that appear from Earth to be close to one another in the sky. [dubious – discuss] This may result from the stars actually being physically close and gravitationally bound to each other, in which case it is a physical multiple star, or this closeness may be merely apparent, in which case it is an optical multiple star [a] Physical multiple ...
This is a list of comets (bodies that travel in elliptical, parabolic, and sometimes hyperbolic orbits and display a tail behind them) listed by type. Comets are sorted into four categories: periodic comets (e.g. Halley's Comet), non-periodic comets (e.g. Comet Hale–Bopp), comets with no meaningful orbit (the Great Comet of 1106), and lost comets (), displayed as either P (periodic), C (non ...