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.

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.

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.