The Collaborative International Dictionary
Magnitude \Mag"ni*tude\, n. [L. magnitudo, from magnus great. See Master, and cf. Maxim.]
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Extent of dimensions; size; -- applied to things that have length, breadth, and thickness.
Conceive those particles of bodies to be so disposed amongst themselves, that the intervals of empty spaces between them may be equal in magnitude to them all.
--Sir I. Newton. (Geom.) That which has one or more of the three dimensions, length, breadth, and thickness.
Anything of which greater or less can be predicated, as time, weight, force, and the like.
Greatness; grandeur. ``With plain, heroic magnitude of mind.''
--Milton.-
Greatness, in reference to influence or effect; importance; as, an affair of magnitude.
The magnitude of his designs.
--Bp. Horsley. -
(Astron.) See magnitude of a star, below. Apparent magnitude
(Opt.), the angular breadth of an object viewed as measured by the angle which it subtends at the eye of the observer; -- called also apparent diameter.
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(Astron.) Same as magnitude of a star, below.
Magnitude of a star (Astron.), the rank of a star with respect to brightness. About twenty very bright stars are said to be of first magnitude, the stars of the sixth magnitude being just visible to the naked eye; called also visual magnitude, apparent magnitude, and simply magnitude. Stars observable only in the telescope are classified down to below the twelfth magnitude. The difference in actual brightness between magnitudes is now specified as a factor of 2.512, i.e. the difference in brightness is 100 for stars differing by five magnitudes.
Wiktionary
n. (context astronomy English) a numerical measure of the brightness of a star, planet etc.; a decrease of 1 unit represents an increase in the light received by a factor of 2.512
Wikipedia
The apparent magnitude (m) of a celestial object is a number that is a measure of its brightness as seen by an observer on Earth. The brighter an object appears, the lower its magnitude value (i.e. inverse relation). The Sun, at apparent magnitude of −27, is the brightest object in the sky. It is adjusted to the value it would have in the absence of the atmosphere. Furthermore, the magnitude scale is logarithmic; a difference of one in magnitude corresponds to a change in brightness by a factor of $\sqrt[5]{100}$, or about 2.512.
Generally, the visible spectrum (vmag) is used as a basis for the apparent magnitude. However, other spectra are also used (e.g. the near-infrared J-band). In the visible spectrum, Sirius is the brightest star after the Sun. In the near-infrared J-band, Betelgeuse is the brightest. The apparent magnitude of stars is measured with a bolometer.
Usage examples of "apparent magnitude".
A last reading with the photocell gave me the apparent magnitude and a comparison with its absolute magnitude showed its distance.
He was rather disposed to suspect that it was not the earth's satellite at all, but some planet with its apparent magnitude greatly enlarged by its approximation to the earth.
And the fit between the curves showing quasar counts by apparent magnitude and luminous Sb spiral galaxies such as M31 and M81—.
Canopus itself was extraordinarily bright -- triple the apparent magnitude of Sirius from Earth (that was not the proper way to express it, but he hardly cared at this moment) -- and Sirius was Earth's brightest star.
Canopus itself was extraordinarily bright-triple the apparent magnitude of Sirius from Earth (that was not the proper way to express it, but he hardly cared at this moment)-and Sirius was Earth's brightest star.
She watched dumbfounded as it brightened over a period of ten seconds, until its apparent magnitude was nearly 2.
The primitive force field generated by a bona fide wedding ceremony was of sufficient authority to dampen the apparent magnitude of a superstar.
Aybee made a quick assessment of its apparent magnitude and decided that they were somewhere on the outer edge of the Kernel Ring.
There were responses to queries by Moonbase research people for project information of one kind or another, studies of chemical components in Arizona soil, comparisons of apparent magnitude of various stars as seen from Australia and the Moon, new information on ocean currents.
It also happens to be a rather dark body--and at its present distance, it has a very low apparent magnitude.