女巫頭星云(Witch Head Nebula)，是一個依照它的形狀而命名的反射星云，它位于波江座內(nèi)，而且受到亮星參宿七 (Rigel)的影響，女巫頭星云的正式的名稱為IC 2118。

簡介

在亮星參宿七的照射下，女巫頭星云(Witch Head Nebula)好像一縷煙霧貫穿波江星座。波江星座距離地球約700光年，是個蜿蜒的、在南北方向延伸的星座，位于獵戶座的西南方向，拉丁語名稱為Eridanus,，意為河流，是意大利的波河在神話中的名字。星云會發(fā)光，是因為星云內(nèi)微細的塵埃，反射參宿七的星光所形成的。女巫頭星云的顏色是藍色的，這不只是因為參宿七是藍色的，而且也是因為星際塵埃的顆粒，對藍光的散射效率比紅光要好。這與地球白天的天空是藍色的道理是一樣的，只是散射源不同而已；地球的藍天是由陽光經(jīng)由空氣中的氮分子與氧分子散射所造成的。這個星云與地球相距約1000光年。

相關(guān)

NASA 美國宇航局每日一圖（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.

獵戶座南方：由腰帶到巫婆星云

說明：你能在這張影像中找到獵戶座的腰帶在哪兒嗎？這三顆肉眼可見的星星可在影像的右上方找到。此外，這張影像是獵戶座南部的大視野深場影像。首先注意到的是腰帶左下方那顆名為參宿一的星星，它照亮了反射星云 M78。在參宿一的正下方，仔細找找可以看到馬頭星云。在下方偏右較遠處則是獵戶座大星云 M42，它本身就是一個肉眼可見的星云。影像中最明亮的一顆星是參宿七，位于接近右下方的位置。明亮的參宿七照亮了代表不吉利的塵埃云，女巫頭星云，它是位于右下角的藍色反射星云。最后，可以看到一個巨大的紅色環(huán)，環(huán)繞著整個獵戶座，它是巴納德環(huán)。如果人類的眼睛感光度增加 10,000 倍，用肉眼就可以看到影像中全部的景像。

NASA 美國宇航局每日一圖（2008.11.31）萬圣節(jié)(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!

說明：在星光下，這一鬼魅的星云閃爍在黑暗的夜空中，曲折的輪廓讓人想起了它的名字――女巫頭星云。事實上，這一望遠鏡拍攝到的迷人肖像，感覺是女巫正緊盯著獵戶座明亮的超巨星參宿七。塵埃狀宇宙星云覆蓋大約50多光年，強烈地反射參宿七發(fā)出的藍光，使它顯現(xiàn)出反射星云典型的色彩。女巫頭星云還被編錄為IC2118，距離我們大約1,000光年遠。當(dāng)然，今晚你可能會看到這一可怕的女巫，但是不必驚慌。是的，祝你度過一個歡快而又安全的萬圣節(jié)。

NASA 美國宇航局每日一圖（2009.12.29） 　Rigel and the Witch Head Nebula

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

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 on the lower left is associated with the bright star Rigel, to its right, in the constellation Orion. More

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.

說明：努力吧！忙碌吧！猛烈的柴火燒煮著沸騰的大鍋—這時候麥克白應(yīng)該去祈求女巫頭星云。影像左下方這個具有形狀暗示性的反射星云與明亮的參宿七（右側(cè)）一起都位于獵戶座內(nèi)。女巫頭星云更多地是被正式稱為IC2118，其發(fā)出的光主要是反射參宿七的星光。星云內(nèi)的塵埃起到了反射星光的作用。在上面影像中，藍色的女巫頭星云以及塵埃圍繞的參宿七不僅僅是由藍色的參宿七造成，而是塵埃微粒反射藍色星光的效應(yīng)比反射紅光強烈的緣故。相同的物理過程還造成了地球白天的天空看上去是藍色的，盡管地球大氣層散射物質(zhì)是氮氣和氧氣。參宿七，女巫頭星云，以及圍繞在它們身邊的氣體與塵埃距離我們大約800光年遠。

NASA 美國宇航局每日一圖（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.

說明：雙雙而至的圈套及困擾、熊熊烈焰和沸騰的氣泡－這一切，也許只有麥克白（莎士比亞悲劇《麥克白》中的主人公）才能與女巫頭星云溝通。這個因形狀而得名的反射星云正式編號為IC 2118，與獵戶座中的亮星參宿七有著不解之緣，它所反射的光芒主要就來自參宿七，它恰好位于下邊緣之外。星云中的細微塵埃能反射星光，但它顯示出的藍色并非只是因參宿七發(fā)出藍光，而是由于塵埃顆粒反射藍光的效率比紅光更高。同樣的物理原理也造成了地球天空在白天看上去是藍色的，只不過地球大氣中的散射源是氮氣及氧氣分子。女巫頭星云距離我們約1000光年。