女巫头星云

波江座内的反射星云

女巫头星云(Witch Head Nebula)，是一个依照它的形状而命名的反射星云，它位于波江座内，而且受到亮星参宿七 (Rigel)的影响，女巫头星云的正式的名称为IC 2118。

简介

在亮星参宿七的照射下，女巫头星云(Witch Head Nebula)好像一缕烟雾贯穿波江星座。波江星座距离地球约700光年，是个蜿蜒的、在南北方向延伸的星座，位于猎户座的西南方向，拉丁语名称为Eridanus,，意为河流，是意大利的波河在神话中的名字。星云会发光，是因为星云内微细的尘埃，反射参宿七的星光所形成的。女巫头星云的颜色是蓝色的，这不只是因为参宿七是蓝色的，而且也是因为星际尘埃的颗粒，对蓝光的散射效率比红光要好。这与地球白天的天空是蓝色的道理是一样的，只是散射源不同而已；地球的蓝天是由阳光经由空气中的氮分子与氧分子散射所造成的。这个星云与地球相距约1000光年。

相关

NASA 美国宇航局每日一图（2008.04.08）

Southern Orion: From Belt to Witch

Explanation: Do you recognize the belt of Orion in this image? The familiar trio of stars, visible to the unaided eye, can be found across the upper left. Otherwise, the southern part of the constellation Orion has taken on a new look inthis unusually deep and wide view First note that the lower left belt star, Alnitak, is the easternmost star in Orion's belt. Left of Alnitak is the Flame Nebula, with clouds of bright emission and dramatic dark dust lanes. Directly belowAlnitak, a close inspection will reveal the Horsehead Nebula. Farther right and below is the Orion Nebula, M42, itself visible to the unaided eye. The brightest star in the frame, near the bottom right, is Rigel. A bright blue star, Rigelilluminates the ominously shaped dust patch known as the Witch Head Nebula, visible as the blue reflection nebula near the lower right corner. Finally, appearing as a vast red ring and encompassing the entire region, is Barnard's Loop.Humans could see this entire menagerie, unaided, were their eyes about 10,000 times more sensitive.

猎户座南方：由腰带到巫婆星云

说明：你能在这张影像中找到猎户座的腰带在哪儿吗？这三颗肉眼可见的星星可在影像的右上方找到。此外，这张影像是猎户座南部的大视野深场影像。首先注意到的是腰带左下方那颗名为参宿一的星星，它照亮了反射星云 M78。在参宿一的正下方，仔细找找可以看到马头星云。在下方偏右较远处则是猎户座大星云 M42，它本身就是一个肉眼可见的星云。影像中最明亮的一颗星是参宿七，位于接近右下方的位置。明亮的参宿七照亮了代表不吉利的尘埃云，女巫头星云，它是位于右下角的蓝色反射星云。最后，可以看到一个巨大的红色环，环绕着整个猎户座，它是巴纳德环。如果人类的眼睛感光度增加 10,000 倍，用肉眼就可以看到影像中全部的景像。

NASA 美国宇航局每日一图（2008.11.31）万圣节(Halloween Night)

By starlight this eerie visage shines in the dark, a crooked profile evoking its popular name, the Witch Head Nebula. In fact, this entrancing telescopic portrait gives the impression the witch has fixed her gaze on Orion's bright supergiant star Rigel. Spanning over 50 light-years, the dusty cosmic cloud strongly reflects nearby Rigel's blue light, giving it the characteristic color of a reflection nebula. Cataloged as IC 2118, the Witch Head Nebula is about 1,000 light-years away. Of course, you might see a witch this scary tonight, but don't panic. Have a safe and Happy Halloween!

说明：在星光下，这一鬼魅的星云闪烁在黑暗的夜空中，曲折的轮廓让人想起了它的名字――女巫头星云。事实上，这一望远镜拍摄到的迷人肖像，感觉是女巫正紧盯着猎户座明亮的超巨星参宿七。尘埃状宇宙星云覆盖大约50多光年，强烈地反射参宿七发出的蓝光，使它显现出反射星云典型的色彩。女巫头星云还被编录为IC2118，距离我们大约1,000光年远。当然，今晚你可能会看到这一可怕的女巫，但是不必惊慌。是的，祝你度过一个欢快而又安全的万圣节。

NASA 美国宇航局每日一图（2009.12.29）　Rigel and the Witch Head Nebula

Credit & Copyright: Rogelio Bernal Andreo (Deep Sky Colors)

formally known as IC 2118, the Witch Head Nebula glows primarily by light reflected from Rigel. Fine dust in the nebula reflects the light. Pictured above, the blue color of the Witch Head Nebula and of the dust surrounding Rigel 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. Rigel, the Witch Head Nebula, and gas and dust that surrounds them lie about 800 light-years away.

说明：努力吧！忙碌吧！猛烈的柴火烧煮着沸腾的大锅—这时候麦克白应该去祈求女巫头星云。影像左下方这个具有形状暗示性的反射星云与明亮的参宿七（右侧）一起都位于猎户座内。女巫头星云更多地是被正式称为IC2118，其发出的光主要是反射参宿七的星光。星云内的尘埃起到了反射星光的作用。在上面影像中，蓝色的女巫头星云以及尘埃围绕的参宿七不仅仅是由蓝色的参宿七造成，而是尘埃微粒反射蓝色星光的效应比反射红光强烈的缘故。相同的物理过程还造成了地球白天的天空看上去是蓝色的，尽管地球大气层散射物质是氮气和氧气。参宿七，女巫头星云，以及围绕在它们身边的气体与尘埃距离我们大约800光年远。

NASA 美国宇航局每日一图（2012.01.17）

IC 2118: The Witch Head Nebula

Image Credit & Copyright: Gimmi Ratto & Davide Bardini (Collecting Photons)

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.

说明：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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