本帖最后由 gohomeman1 于 2010-5-6 17:31 编辑
On Earth, we tend to find dust nothing more than a nuisance that blankets our furniture and causes us to sneeze. Cosmic dust can also be a hindrance to astronomers because cameras using visible light cannot see through it. However, studying cosmic dust in detail helps astronomers to pin down the ingredients of the raw mixture that eventually gives birth to stars.
在地球上，我们对尘埃的感觉倾向于弄脏我们的家具、甚至导致我们打喷嚏。对天文学家来说，宇宙尘埃也很讨厌，因为它们遮蔽了可见光。但是，宇宙尘埃的详细研究有助于天文学家确定最终成为恒星诞生的原始混合物。
This close-up of an area in the northwest region of the large Iris Nebula seems to be clogged with cosmic dust. With bright light from the nearby star HD 200775 [1] illuminating it from above, the dust resembles thick mounds of billowing cotton. It is actually made up of tiny particles of solid matter, with sizes from ten to a hundred times smaller than those of the dust grains we find at home [2]. Both background and foreground stars are dotted throughout the image.
本图是巨大的Iris星云西北部区域的特写，看来充斥着宇宙尘埃。沐浴在图外上方的明亮巨星HD 200775的星光下（注1），尘埃就像巨厚的棉花山般起伏。它们其实有细微的固体粒子组成，仅为我们家里发现的尘埃颗粒大小的1/10~1/100。画面中星罗棋布的红点是前景星和背景星。
NGC 7023 is a reflection nebula, which means it scatters light from a massive nearby star, in this case, HD 200775. Reflection nebulae are different from emission nebulae, which are clouds of gas that are hot enough to emit light themselves. Reflection nebulae tend to appear blue because of the way light scatters, but parts of the Iris Nebula appear unusually red.
NGC 7023是反射星云，也就是说，尘埃散射附近大质量恒星的星光才被我们看见。本例中，就是HD 200775（在DSS2大图中就是中央蓝巨星）。反射星云与发射星云不同，后者主要由灼热到能发射可见光的气体组成。因为散射的缘故，反射星云偏向于蓝色，但NGC 7023部分显示为不常见的红色。
Researchers studying the object are particularly interested in the region to the left and slightly above centre in the image, where they find dusty filaments to be redder than expected. An unknown chemical compound, most likely based on hydrocarbons, is responsible for the red tinge. The high resolution and sensitivity of Hubble’s instruments allow astronomers to study the area in detail. Images and spectra are only part of the analysis. On Earth, scientists are performing additional laboratory tests to assess better the exact chemical composition of the nebula.
研究者对图中左边延伸到中央的尘埃区域特别地感兴趣，因为这里的尘埃细丝呈现出乎意料的暗红色。一种未知的化合物，很可能是碳氢化合物，产生了这种微红色反光。哈勃高分辨率、高灵敏度的仪器给天文学家提供了该区域的详尽细节。数据分析不仅是照片和光谱，科学家还在地面实验室中进行各种化合物（光谱）实验，以更好地确定星云的化学组成。
NGC 7023 was discovered by Sir William Herschel in 1794; the nebula is in the constellation of Cepheus, the King, in the northern sky. NGC 7023 is approximately 1400 light–years from Earth and about six light-years across. This aethereal image was taken by Hubble's Advanced Camera for Surveys. Astronomers also used Hubble’s Near Infrared Camera and Multi-Object Spectrometer (NICMOS) instrument to try to determine which chemical elements are present in the nebula.
1794年，小威廉.赫歇尔发现了NGC 7023，它位于北天的仙王座，离地球约1400光年，本身大约6光年宽。本张飘逸的图像由哈勃的高级巡天相机（ACS）拍摄。天文学家还使用了哈勃的近红外相机和多目标光谱仪（NICMOS）以探索星云的化学元素组成。
PS：由于NICMOS已经宕掉很多年了，哈勃官网到今天还没宣布它已经可以投入科学工作。所以我认为本图如果不是5年前就拍摄的，就是今年刚拍摄的，NICMOS现在处于测试期中。——gohomeman1注 |
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