# magnitude

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magnitude
(mag)
1. a unit traditionally used in astronomy to express the apparent brightness of stars, planets, and other objects in the sky. For centuries, the brightest stars were said to be of the "first magnitude," with fainter ones of the "second magnitude" and so on down to "sixth magnitude" for the faintest stars visible to the unaided eye. When it became possible to measure stellar brightnesses precisely, it was discovered that stars of a given traditional magnitude were roughly 2.5 times brighter than stars of the next magnitude. Astronomers agreed to define the magnitude scale so that a difference of exactly 5.0 mag corresponds to a brightness difference of exactly 100 times. A difference of 1.0 mag then corresponds to a brightness difference of the fifth root of 100 or about 2.512 times. The scale is upside down: brighter stars have lower, not higher magnitudes, in keeping with the historical origin of the scale. The zero point (0.0 mag) is set arbitrarily so that the stars historically listed as "first magnitude" have magnitude measurements of 1.5 mag or brighter. The brightest stars and planets have negative magnitudes on this scale.
2. a unit used in earth science to measure the intensity of earthquakes. Geologists actually use several scales to measure earthquake intensity, but the one best known to the public is the Richter magnitude scale, developed in 1935 by Charles F. Richter (1900-1985) of the California Institute of Technology. The Richter magnitude is computed from the measured amplitude and frequency of the earthquake's shock waves received by a seismograph, adjusted to account for the distance between the observing station and the epicenter of the earthquake. An increase of 1.0 in the Richter magnitude corresponds to an increase of 10 times in the amplitude of the waves and to an increase of about 31 times more energy released by the quake. The most powerful earthquakes recorded so far had magnitudes of about 8.5. The Richter magnitude measures the intensity of the earthquake itself, not the intensity of the earthquake's effects: the effects also depend on the depth of the earthquake, the geology of the area around the epicenter, and many other factors. Earthquake effects are rated using the Mercalli scale (see below).

Dictionary of units of measurement. 2015.

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• magnitude — [ maɲityd ] n. f. • 1892; « grandeur, puissance » 1372; lat. magnitudo 1 ♦ Astron. Magnitude apparente : nombre caractéristique du flux de rayonnement reçu d un astre. 2 ♦ Géophys. Magnitude d un séisme : son énergie totale, mesurée selon une… …   Encyclopédie Universelle

• Magnitude — may refer to: In mathematics: Magnitude (mathematics), the relative size of a mathematical object Magnitude (vector), a term for the size or length of a vector Scalar (mathematics), a quantity defined only by its magnitude Euclidean vector, a… …   Wikipedia

• Magnitude — Mag ni*tude, n. [L. magnitudo, from magnus great. See {Master}, and cf. {Maxim}.] 1. Extent of dimensions; size; applied to things that have length, breadth, and thickness. [1913 Webster] Conceive those particles of bodies to be so disposed… …   The Collaborative International Dictionary of English

• magnitude — Mag ni*tude, n. [L. magnitudo, from magnus great. See {Master}, and cf. {Maxim}.] 1. Extent of dimensions; size; applied to things that have length, breadth, and thickness. [1913 Webster] Conceive those particles of bodies to be so disposed… …   The Collaborative International Dictionary of English

• magnitude — [mag′nə to͞od΄, mag′nətyo͞od΄] n. [L magnitudo < magnus, great: see MAGNI ] 1. greatness; specif., a) of size b) of extent c) of importance or influence d) Obs. of character 2 …   English World dictionary

• Magnitude 10,5 — Données clés Titre original 10.5 Réalisation John Lafia Scénario Christopher Canaan, Ronnie Christensen, John Lafia Pays d’origine États Unis Genre Catastrophe …   Wikipédia en Français

• magnitude — [n1] importance consequence, degree, eminence, grandeur, greatness, import, mark, moment, momentousness, note, pith, significance, signification, weight, weightiness; concept 668 Ant. insignificance, unimportance magnitude [n2] size admeasurement …   New thesaurus

• magnitude — I noun amplitude, amplitudo, bearing, concern, consequence, consideration, degree, dimension, effect, eminence, enormity, essentiality, extension, extent, gauge, gravity, immensity, import, importance, magnitudo, mark, materiality, materialness,… …   Law dictionary

• magnitude — (n.) c.1400, greatness of size or character, from L. magnitudo greatness, bulk, size, from magnus great (see MAGNATE (Cf. magnate)) + tudo, suffix forming abstract nouns from adjectives and participles (see TUDE (Cf. tude)). Meaning size, extent… …   Etymology dictionary

• magnitude — s. f. 1. Qualidade do que é magno. 2. Importância; grandeza …   Dicionário da Língua Portuguesa

• magnitude — volume, *size, extent, dimensions, area Analogous words: amplitude, *expanse, stretch, spread: *bulk, mass, volume …   New Dictionary of Synonyms