absolute magnitude


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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. A.D.), 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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absolute magnitude

See magnitude.
Collins Dictionary of Astronomy © Market House Books Ltd, 2006

absolute magnitude

[′ab·sə‚lüt ′mag·nə·tüd]
(astrophysics)
A measure of the brightness of a star equal to the magnitude the star would have at a distance of 10 parsecs from the observer.
The stellar magnitude any meteor would have if placed in the observer's zenith at a height of 100 kilometers.
(mathematics)
The absolute value of a number or quantity.
McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, Copyright © 2003 by The McGraw-Hill Companies, Inc.
References in periodicals archive ?
Consistent with the magnet hypothesis, the absolute magnitude of [[phi].sub.0] is higher in the limit period than the no-limit period for both upper and lower limits.
We develop separate change measures of absolute magnitude and relative magnitude, which are the difference in the number of Japanese FDIs and the annual growth rate of Japanese FDIs (by industry), respectively.
By Absolute magnitude, astronomers mean the apparent magnitude that a star would have if it was situated a standard distance of 36.2 light-years from Earth.
Recognizing the Relative and Absolute Magnitude of Numbers
The potential error in growth estimates will then be directly proportional to both the relative and absolute magnitude of shrinkage.
We find that accrual quality is negatively related to the absolute magnitude of accruals, the length of the operating cycle, loss incidence, and the standard deviation of sales, cash flows, accruals, and earnings, and positively related to firm size.
Number sense involves the ability to recognize the relative and absolute magnitude of numbers (Sowder 1992).
Bearing the burden While smaller in absolute magnitude than the costs associated with environmental, economic, and tax compliance regulations, workplace regulations nevertheless represent a significant burden on all Americans.
"Whilst the absolute magnitude of the economic impact seems large, it is 2percent of the regional turnover and less than 1percent of total regional employment.
If it is assumed that interstellar extinction is negligible then the surface brightness and absolute magnitude of NGC 6210 can be determined.
However, although an order of magnitude lower in absolute magnitude of warp deformation and stress, CuW structures exhibited significant changes in warp deformation (36 to 50 percent) for both base-flange thickness and assembly brazing/process temperature.
For example, about two-thirds of annual job creation and destruction are accounted for by establishments with growth rates above 25 percent in absolute magnitude. Of this group, plant start-ups account for 12 percent of annual job creation, while plant shutdowns account for about 23 percent of annual job destruction.