—magnitudinous /mag'ni toohd"n euhs, -tyoohd"-/, adj./mag"ni toohd', -tyoohd'/, n.1. size; extent; dimensions: to determine the magnitude of an angle.2. great importance or consequence: affairs of magnitude.3. greatness of size or amount.4. moral greatness: magnitude of mind.5. Astron.a. Also called visual magnitude, apparent magnitude. the brightness of a star or other celestial body as viewed by the unaided eye and expressed by a mathematical ratio of 2.512: a star of the first magnitude is approximately 21/2 times as bright as one of the second magnitude and 100 times brighter than one of the sixth magnitude. Only stars of the sixth magnitude or brighter can be seen with the unaided eye.b. See absolute magnitude.6. Math. a number characteristic of a quantity and forming a basis for comparison with similar quantities, as length.7. of the first magnitude, of utmost or major importance: an artist of the first magnitude.[1350-1400; ME < L magnitudo. See MAGNI-, -TUDE]
* * *In astronomy, the measure of the brightness of a star or other celestial body.The brighter the object, the lower the number assigned as a magnitude. In ancient times six magnitude classes were used, the first containing the brightest stars (see Hipparchus). In the present system a difference of one magnitude is defined as a ratio of brightness of 2.512 times. Thus, a difference of five magnitudes corresponds to a brightness ratio of 100 to 1. Apparent magnitude is an object's brightness as seen from Earth (e.g., -26.7 for the Sun, about -11 for the Moon). Absolute magnitude is an object's brightness as it would be seen at a distance of 10 parsecs (32.6 light-years; e.g., 4.8 for the Sun). See also albedo; photometry.
* * *in astronomy, measure of the brightness of a star or other celestial body. The brighter the object, the lower the number assigned as a magnitude. In ancient times, stars were ranked in six magnitude classes, the first magnitude class containing the brightest stars. In 1850 the English astronomer Norman Robert Pogson proposed the system presently in use. One magnitude is defined as a ratio of brightness of 2.512 times; e.g., a star of magnitude 5.0 is 2.512 times as bright as one of magnitude 6.0. Thus, a difference of five magnitudes corresponds to a brightness ratio of 100 to 1. After standardization and assignment of the zero point, the brightest class was found to contain too great a range of luminosities, and negative magnitudes were introduced to spread the range.Apparent magnitude is the brightness of an object as it appears to an observer on Earth. The Sun's apparent magnitude is −26.7, that of the full Moon is about −11, and that of the bright star Sirius, −1.5. The faintest objects visible through the Hubble Space Telescope are of (approximately) apparent magnitude 30. Absolute magnitude is the brightness an object would exhibit if viewed from a distance of 10 parsecs (32.6 light-years). The Sun's absolute magnitude is 4.8.Bolometric magnitude is that measured by including a star's entire radiation, not just the portion visible as light. Monochromatic magnitude is that measured only in some very narrow segment of the spectrum. Narrow-band magnitudes are based on slightly wider segments of the spectrum and broad-band magnitudes on areas wider still. Visual magnitude may be called yellow magnitude because the eye is most sensitive to light of that colour. (See also colour index).
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