8. 天文学中为了衡量星星的明暗程度,古希腊天文学家喜帕恰斯(
![](http://math.21cnjy.com/mml2svg?mml=%3Cmath+xmlns%3D%22http%3A%2F%2Fwww.w3.org%2F1998%2FMath%2FMathML%22%3E%3Cmrow%3E%3Cmi%3EH%3C%2Fmi%3E%3Cmi%3Ei%3C%2Fmi%3E%3Cmi%3Ep%3C%2Fmi%3E%3Cmi%3Ep%3C%2Fmi%3E%3Cmi%3Ea%3C%2Fmi%3E%3Cmi%3Er%3C%2Fmi%3E%3Cmi%3Ec%3C%2Fmi%3E%3Cmi%3Eh%3C%2Fmi%3E%3Cmi%3Eu%3C%2Fmi%3E%3Cmi%3Es%3C%2Fmi%3E%3C%2Fmrow%3E%3C%2Fmath%3E)
,又名依巴谷)在公元前二世纪首先提出了星等这个概念.星等的数值越小,星星就越亮;星等的数值越大,它的光就越暗.到了1850年,由于光度计在天体光度测量中的应用,英国天文学家普森(
![](http://math.21cnjy.com/mml2svg?mml=%3Cmath+xmlns%3D%22http%3A%2F%2Fwww.w3.org%2F1998%2FMath%2FMathML%22%3E%3Cmrow%3E%3Cmi%3EM%3C%2Fmi%3E%3Cmo%3E.%3C%2Fmo%3E%3Cmi%3ER%3C%2Fmi%3E%3Cmo%3E.%3C%2Fmo%3E%3Cmi%3EP%3C%2Fmi%3E%3Cmi%3Eo%3C%2Fmi%3E%3Cmi%3Eg%3C%2Fmi%3E%3Cmi%3Es%3C%2Fmi%3E%3Cmi%3Eo%3C%2Fmi%3E%3Cmi%3En%3C%2Fmi%3E%3C%2Fmrow%3E%3C%2Fmath%3E)
)又提出了衡量天体明暗程度的亮度的概念.天体的明暗程度可以用星等或亮度来描述.两颗星的星等与亮度满足
![](http://math.21cnjy.com/mml2svg?mml=%3Cmath+xmlns%3D%22http%3A%2F%2Fwww.w3.org%2F1998%2FMath%2FMathML%22%3E%3Cmrow%3E%3Cmsub%3E%3Cmi%3Em%3C%2Fmi%3E%3Cmn%3E1%3C%2Fmn%3E%3C%2Fmsub%3E%3Cmo%3E%E2%88%92%3C%2Fmo%3E%3Cmsub%3E%3Cmi%3Em%3C%2Fmi%3E%3Cmn%3E2%3C%2Fmn%3E%3C%2Fmsub%3E%3Cmo%3E%3D%3C%2Fmo%3E%3Cmtext%3E%26nbsp%3B%3C%2Fmtext%3E%3Cmn%3E2.5%3C%2Fmn%3E%3Cmrow%3E%3Cmo%3E%28%3C%2Fmo%3E%3Cmrow%3E%3Cmi%3Elg%3C%2Fmi%3E%3Cmsub%3E%3Cmi%3EE%3C%2Fmi%3E%3Cmn%3E2%3C%2Fmn%3E%3C%2Fmsub%3E%3Cmo%3E%E2%88%92%3C%2Fmo%3E%3Cmi%3Elg%3C%2Fmi%3E%3Cmsub%3E%3Cmi%3EE%3C%2Fmi%3E%3Cmn%3E1%3C%2Fmn%3E%3C%2Fmsub%3E%3C%2Fmrow%3E%3Cmo%3E%29%3C%2Fmo%3E%3C%2Fmrow%3E%3C%2Fmrow%3E%3C%2Fmath%3E)
.其中星等为
![](http://math.21cnjy.com/mml2svg?mml=%3Cmath+xmlns%3D%22http%3A%2F%2Fwww.w3.org%2F1998%2FMath%2FMathML%22%3E%3Cmrow%3E%3Cmsub%3E%3Cmi%3Em%3C%2Fmi%3E%3Cmi%3Ei%3C%2Fmi%3E%3C%2Fmsub%3E%3C%2Fmrow%3E%3C%2Fmath%3E)
的星的亮度为
![](http://math.21cnjy.com/mml2svg?mml=%3Cmath+xmlns%3D%22http%3A%2F%2Fwww.w3.org%2F1998%2FMath%2FMathML%22%3E%3Cmrow%3E%3Cmsub%3E%3Cmi%3EE%3C%2Fmi%3E%3Cmi%3Ei%3C%2Fmi%3E%3C%2Fmsub%3E%3Cmrow%3E%3Cmo%3E%28%3C%2Fmo%3E%3Cmrow%3E%3Cmi%3Ei%3C%2Fmi%3E%3Cmo%3E%3D%3C%2Fmo%3E%3Cmn%3E1%3C%2Fmn%3E%3Cmo%3E%2C%3C%2Fmo%3E%3Cmn%3E2%3C%2Fmn%3E%3C%2Fmrow%3E%3Cmo%3E%29%3C%2Fmo%3E%3C%2Fmrow%3E%3C%2Fmrow%3E%3C%2Fmath%3E)
.已知“心宿二”的星等是1.00.“天津四” 的星等是1.25.“心宿二”的亮度是“天津四”的
![](http://math.21cnjy.com/mml2svg?mml=%3Cmath+xmlns%3D%22http%3A%2F%2Fwww.w3.org%2F1998%2FMath%2FMathML%22%3E%3Cmi%3Er%3C%2Fmi%3E%3C%2Fmath%3E)
倍,则与
![](http://math.21cnjy.com/mml2svg?mml=%3Cmath+xmlns%3D%22http%3A%2F%2Fwww.w3.org%2F1998%2FMath%2FMathML%22%3E%3Cmi%3Er%3C%2Fmi%3E%3C%2Fmath%3E)
最接近的是(当
![](http://math.21cnjy.com/mml2svg?mml=%3Cmath+xmlns%3D%22http%3A%2F%2Fwww.w3.org%2F1998%2FMath%2FMathML%22%3E%3Cmrow%3E%3Cmrow%3E%3Cmo%3E%7C%3C%2Fmo%3E%3Cmi%3Ex%3C%2Fmi%3E%3Cmo%3E%7C%3C%2Fmo%3E%3C%2Fmrow%3E%3C%2Fmrow%3E%3C%2Fmath%3E)
较小时,
![](http://math.21cnjy.com/mml2svg?mml=%3Cmath+xmlns%3D%22http%3A%2F%2Fwww.w3.org%2F1998%2FMath%2FMathML%22%3E%3Cmrow%3E%3Cmsup%3E%3Cmrow%3E%3Cmn%3E10%3C%2Fmn%3E%3C%2Fmrow%3E%3Cmi%3Ex%3C%2Fmi%3E%3C%2Fmsup%3E%3Cmo%3E%E2%89%88%3C%2Fmo%3E%3Cmn%3E1%3C%2Fmn%3E%3Cmo%3E%2B%3C%2Fmo%3E%3Cmn%3E2.3%3C%2Fmn%3E%3Cmi%3Ex%3C%2Fmi%3E%3Cmo%3E%2B%3C%2Fmo%3E%3Cmn%3E2.7%3C%2Fmn%3E%3Cmsup%3E%3Cmi%3Ex%3C%2Fmi%3E%3Cmn%3E2%3C%2Fmn%3E%3C%2Fmsup%3E%3C%2Fmrow%3E%3C%2Fmath%3E)
)