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The jansky (symbol Jy) is a non-SI unit of spectral flux density,〔http://science.jrank.org/pages/57879/jansky.html 〕 or spectral irradiance, equivalent to 10−26 watts per square metre per hertz. The ''flux density'' or ''monochromatic flux'', , of a source is the integral of the spectral radiance, , over the source solid angle: The unit is named after pioneering US radio astronomer Karl Guthe Jansky, and is defined as: (SI) (cgs)〔〕 Since the jansky is obtained by integrating over the whole source solid angle, it is most simply used to describe point sources; for example, the Third Cambridge Catalogue of Radio Sources (3C) reports results in Jy. * For extended sources, the surface brightness is often described with units of Jy per solid angle; for example, Far Infra-Red (FIR) maps from the IRAS satellite are in MJy/sr. * While extended sources at all wavelengths can be reported with these units, for radio frequency maps, extended sources have traditionally been described in terms of a brightness temperature; for example the (Haslam et al. ) 408 MHz all-sky continuum survey is reported in terms of a brightness temperature in K. ==Unit conversions== Jansky units are not a standard SI Unit, so it may be imperative to convert the unit to Watts. However, other unit conversions are possible with respect to measuring this unit. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「jansky」の詳細全文を読む スポンサード リンク
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