双双而至的圈套及困扰、熊熊烈焰和沸腾的气泡 - 这一切,也许只有麦克白(莎士比亚悲剧《麦克白》中的主人公)才能与女巫头星云沟通。这个因形状而得名的反射星云正式编号为 IC 2118,与猎户座中的亮星参宿七有着不解之缘,它所反射的光芒主要就来自参宿七,它恰好位于上图的下边缘之外。星云中的细微尘埃能反射星光,但它显示出的蓝色并非只是因参宿七发出蓝光,而是由于尘埃颗粒反射蓝光的效率比红光更高。同样的物理原理也造成了地球天空在白天看上去是蓝色的,只不过地球大气中的散射源是氮气及氧气分子。女巫头星云距离我们约1000光年。
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Explanation: Double, double toil and trouble; Fire burn, and cauldron bubble -- maybe Macbeth should have consulted the Witch Head Nebula. This suggestively shaped reflection nebula is associated with the bright star Rigel in the constellation Orion. More formally known as IC 2118, the Witch Head Nebula glows primarily by light reflected from bright star Rigel, located just below the lower edge of the above image. Fine dust in the nebula reflects the light. The blue color is caused not only by Rigel's blue color but because the dust grains reflect blue light more efficiently than red. The same physical process causes Earth's daytime sky to appear blue, although the scatterers in Earth's atmosphere are molecules of nitrogen and oxygen. The nebula lies about 1000 light-years away.
每日天文一图(APOD)是美国宇航局天体物理学部每日定期发布的天文图片,并配有专业的简短解释,是小子时常光顾的地方,地址为:http://apod.nasa.gov/apod/。现将部分酷图转来并对原文解释做了翻译,英文及天文知识均有限,译错之处敬请各位指正。
秋天的麦兜 2012年1月17日 于济南。
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