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magnitude

magnitude, in astronomy, measure of the brightness of a star or other celestial object. The stars cataloged by Ptolemy (2d cent. AD), all visible with the unaided eye, were ranked on a brightness scale such that the brightest stars were of 1st magnitude and the dimmest stars were of 6th magnitude. The modern magnitude scale was placed on a precise basis by N. R. Pogson (1856). It was found by photometric measurements that stars of the 1st magnitude were about 100 times as bright as stars of the 6th magnitude, i.e., 5 magnitudes lower. Pogson defined a difference of 5 magnitudes to be exactly equal to a hundredfold change in brightness, so that stars differing by 1 magnitude differ in brightness by a factor of 2.512 (the 5th root of 100). The modern magnitude scale permits a precise expression of a star's relative brightness and extends to both extremely bright and very dim objects. Thus, an object 2.512 times as bright as a 1st-magnitude star is of 0 magnitude; brighter objects have negative magnitudes. The sun's magnitude, for example, is -26.8. On the other hand, a faint star of 16th magnitude is only 1/10,000 as bright as a 6th-magnitude star, the dimmest that can be seen with the naked eye. Magnitudes determined on the basis of an object's relative brightness as seen from the earth are known as apparent magnitudes. Astronomers also assign a star an absolute magnitude, which is the magnitude that a star would have if it were located at a standard distance of 10 parsecs (32.6 light-years). Absolute magnitude is a measure of the intrinsic luminosity of the star, i.e., its true brightness. Since in modern times magnitudes are measured with photometers and electronic detectors, which may be more sensitive to light at one wavelength than at another wavelength, it is necessary to specify the method and the filter used when comparing two or more magnitudes. The magnitude usually referred to is the visual, or photovisual, magnitude, measured with a photometer.

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magnitude

mag·ni·tude / ˈmagnəˌtoōd/ • n. 1. the great size or extent of something: they may feel discouraged at the magnitude of the task before them. ∎  great importance: events of tragic magnitude. 2. size: electorates of less than average magnitude. ∎  a numerical quantity or value: the magnitudes of all the economic variables could be determined. 3. the degree of brightness of a star. The magnitude of an astronomical object is now reckoned as the negative logarithm of the brightness; a decrease of one magnitude represents an increase in brightness of 2.512 times. A star with an apparent magnitude of six is barely visible to the naked eye.See also apparent magnitude, absolute magnitude. ∎  the class into which a star falls by virtue of its brightness. ∎  a difference of one on a scale of brightness, treated as a unit of measurement. PHRASES: of the first magnitudesee first.

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magnitude

magnitude In astronomy, numerical value expressing the brightness of a celestial object on a logarithmic scale. Apparent magnitude is the magnitude as seen from Earth, determined by eye, photographically or photometrically. It ranges from positive through zero to negative values, the brightness increasing as the magnitude decreases. Absolute magnitude indicates intrinsic luminosity, and is defined as the apparent magnitude of an object at a distance of 10 parsecs from the object.

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magnitude

magnitude greatness XIV; (relative) size XVI. — L. magnitūdō, f. magnus great, large, rel. to Gr. mégas (cf. MEGA-), Skr. mahā́nt- great, Gmc. *mikil- MUCH; see -TUDE.

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magnitude

magnitudeallude, brood, collude, conclude, crude, delude, dude, elude, étude, exclude, extrude, exude, feud, food, illude, include, intrude, Jude, lewd, mood, nude, obtrude, occlude, Oudh, preclude, protrude, prude, pseud, pultrude, rood, rude, seclude, shrewd, snood, transude, unglued, unsubdued, who'd, you'd •habitude •magnitude • seafood • wholefood •Quaalude • postlude • interlude •Ermintrude • Gertrude • unvalued •prelude • quietude • hebetude •longitude • amplitude •similitude, verisimilitude •solitude • plenitude • finitude •decrepitude • turpitude • pulchritude •crassitude, lassitude •solicitude, vicissitude •attitude, beatitude, gratitude, latitude, platitude •exactitude • sanctitude • aptitude •rectitude • ineptitude • promptitude •fortitude • multitude • certitude •servitude • consuetude

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