AB magnitude system râžmân-e borz-e AB Fr.: système de magnitudes AB A → photometric system defined by reference to → monochromatic magnitudes in such a way that, when monochromatic → flux f_{ν} is measured in ergs sec^{-1} cm^{-2} Hz^{-1}, the magnitude will be: AB = -2.5 logf_{ν} - 48.60. The constant is set so that AB is equal to the V magnitude for a source with a flat → spectral energy distribution. The → zero point is defined by the flux of the star → Vega at 5546 Å. In this system, an object with constant flux per unit frequency interval has zero color. |
absolute magnitude borz-e avast Fr.: magnitude absolue 1) The → magnitude a star would have if it were at a
distance of 10 → parsecs in a void space, without
→ interstellar absorption.
The absolute magnitude is usually deduced from the
→ visual magnitude, measured through a V filter
(→ UBV system), when it is written as M_{V}. If
it is defined for another wavelength, it gets another index (U, B, etc).
If the radiation on all wavelengths is included, it becomes absolute
→ bolometric magnitude, M_{bol}.
The Sun has the absolute magnitude + 4.8. Most of the stars have absolute magnitudes ranging
between -9 (→ supergiants) and + 19
(→ red dwarfs)
(M.S.: SDE). |
apparent magnitude borz-e padidâr Fr.: magnitude apparente A measure of a star's observed brightness (opposed to → absolute magnitude); symbol m. It depends on the star's → intrinsic brightness, its distance from the observer, and the amount of → interstellar absorption. The brightest star → Sirius has an apparent magnitude of -1.46, while the weakest stars visible with the naked eye in the most favorable observation conditions have magnitudes of about +6.5. The stars of magnitudes less than +23 are measured by professional observatories, whereas those of magnitudes less than +30 by a telescope such as the → Hubble Space Telescope (M.S.: SDE). |
apparent visual magnitude borz-e didegâni-ye padidâr Fr.: magnitude visuelle apparente → Apparent magnitude in the visual wavelengths, around 5600 Å. → visual magnitude. |
bolometric magnitude borz-e tafsanji, ~ tafsanjik Fr.: magnitude bolométrique The magnitude of an astronomical object for the entire range of its electromagnetic spectrum. → bolometric; → magnitude. |
color-magnitude diagram nemudâr-e rang-borz Fr.: diagramme couleur-magnitude A form of → Hertzsprung-Russell diagram in which the visual absolute magnitude M_{v} is the vertical axis and the → color index the horizontal axis. |
completeness magnitude borz-e ospori Fr.: magnitude de complétude In photometric studies of a → population of astronomical objects (usually stars or galaxies), the magnitude that represents the faintest members of the population. → completeness; → magnitude. |
de-reddened magnitude borz-e vâsorxidé Fr.: magnitude dérougie A magnitude which has been corrected for the interstellar reddening. De-reddened, p.p. of → de-redden; → magnitude. Borz, → magnitude; vâsorxidé p.p. of vâsorxidan, → de-redden. |
eclipse magnitude borz-e xorgereft Fr.: grandeur de l'éclipse, magnitude ~ ~ The fraction of the Sun's diameter occulted by the Moon. It is strictly a ratio of diameters and should not be confused with → eclipse obscuration, which is a measure of the Sun's surface area occulted by the Moon. Eclipse magnitude may be expressed as either a percentage or a decimal fraction (e.g., 50% or 0.50). By convention, its value is given at the instant of → greatest eclipse (F. Espenak, NASA). |
instrumental magnitude borz-e sâzâli Fr.: magnitude instrumentale The magnitude derived directly using → Pogson's relation. The instrumental magnitude depends on → detector→ sensitivity, telescope → aperture, exact filter → bandpass, etc. It must be → calibrated to some standard → photometric system. → instrumental; → magnitude. |
integrated magnitude borz-e dorostâlidé Fr.: magnitude intégrée The magnitude an extended object (nebula, galaxy,etc.) would have if all of its light were concentrated into a point source |
limiting magnitude borz-e hadd Fr.: magnitude limite The faintest magnitude reachable by an instrument. |
magnitude borz, qadr (#) Fr.: magnitude A measure of brightness in astronomy on a → logarithmic scale in which a difference of five magnitudes represents a difference of 100 times in brightness. In this scale the lower a magnitude, the brighter the object. The faintest magnitude reached by → unaided eye is 6. From L. magnitudo "greatness, bulk, size," from magnus "great," cognate with Pers. meh "great, large" (Mid.Pers. meh, mas; Av. maz-, masan-, mazant- "great, important," mazan- "greatness, majesty," mazišta- "greatest;" cf. Skt. mah-, mahant-; Gk. megas; PIE *meg- "great") + -tudo, suffix forming abstract nouns from adjectives and participles. Borz "height, magnitude" (it occurs also in the name of the mountain chain Alborz), related to boland "high," bâlâ "up, above, high, elevated, height," berg "mountain, hill" (Mid.Pers. buland "high;" O.Pers. baršan- "height;" Av. barəz- "high, mount," barezan- "height;" cf. Skt. bhrant- "high;" L. fortis "strong" (Fr. & E. force); O.E. burg, burh "castle, fortified place," from P.Gmc. *burgs "fortress;" Ger. Burg "castle," Goth. baurgs "city," E. burg, borough, Fr. bourgeois, bourgeoisie, faubourg); PIE base *bhergh- "high"). Qadr, from Ar. |
magnitude scale marpel-e borzhâ Fr.: échelle de magnitudes A scale for measuring and comparing the brightness of astronomical objects. |
magnitude-limited survey bardid bâ borz-e haddmand Fr.: relevé limité en magnitude A survey in which the observed objects are bighter than a given → apparent magnitude. |
order of magnitude râye-ye borz Fr.: ordre de grandeur Value of a number or of a physical quantity given roughly, usually expressed as a power of 10. Thus, 2.5 x 10^{5} and 6.4 x 10^{5} are of the same order of magnitude, and 2 x 10^{7} is 2 orders of magnitude greater than either. |
photoelectric magnitude borz-e šidsanjik, ~ nursanjik Fr.: magnitude photoélectrique The magnitude of an object as measured with a photoelectric photometer. → photoelectric; → magnitude. |
photographic magnitude borz-e aksbardârik Fr.: magnitude photographique The apparent magnitude of a star as determined by measuring its brightness on a photographic plate. The photographic magnitude scale is now considered obsolete. Adj. of → photography; → magnitude. |
photovisual magnitude borz-e šidcašmi Fr.: magnitude photovisuelle Magnitude defined for the combination of a photographic plate and a yellow filter, approximating the spectral sensitivity of the eye. |
visual magnitude borz-e didgâni Fr.: magnitude visuelle The → apparent magnitude of a celestial body in the color sensitivity region of the human eye at a wavelength of 5600 Å. Visual magnitude is now essentially synonymous with V magnitude, which is determined photometrically. |