Discover the cosmos! Each day a different image or photograph of our fascinating universe is featured, along with a brief explanation written by a professional astronomer. 2008 March 8

M104 Hubble Remix
M104的哈勃合成图景

Credit & Copyright: Vicent Peris (OAUV / PTeam), MAST, STScI, AURA, NASA
Explanation: The striking spiral galaxy M104 is famous for its nearly edge-on profile featuring a broad ring of obscuring dust. Seen in silhouette against a bright bulge of stars, the swath of cosmic dust lanes lends a hat-like appearance to the galaxy in optical images suggesting the more popular moniker, The Sombrero Galaxy. Here, Hubble Space Telescope archival image data has been reprocessed to create this alternative look at the well-known galaxy. The newly developed processing improves the visibility of details otherwise lost in overwhelming glare, in this case allowing features of the galaxy's dust lanes to be followed well into the bright central region. About 50,000 light-years across and 28 million light-years away, M104 is one of the largest galaxies at the southern edge of the Virgo Galaxy Cluster.

Discover the cosmos! Each day a different image or photograph of our fascinating universe is featured, along with a brief explanation written by a professional astronomer. 2008 March 9

CMBR Dipole: Speeding Through the Universe
宇宙微波背景辐射偶极子：加速穿越宇宙

Credit: DMR, COBE, NASA, Four-Year Sky Map
Explanation: Our Earth is not at rest. The Earth moves around the Sun. The Sun orbits the center of the Milky Way Galaxy. The Milky Way Galaxy orbits in the Local Group of Galaxies. The Local Group falls toward the Virgo Cluster of Galaxies. But these speeds are less than the speed that all of these objects together move relative to the cosmic microwave background radiation (CMBR). In the above all-sky map from the COBE satellite, radiation in the Earth's direction of motion appears blueshifted and hence hotter, while radiation on the opposite side of the sky is redshifted and colder. The map indicates that the Local Group moves at about 600 kilometers per second relative to this primordial radiation. This high speed was initially unexpected and its magnitude is still unexplained. Why are we moving so fast? What is out there?

[ 本帖最后由 咖啡君 于 2008-3-12 10:17 编辑 ]

Discover the cosmos! Each day a different image or photograph of our fascinating universe is featured, along with a brief explanation written by a professional astronomer. 2008 March 10

Planets Align Over Australian Radio Telescope Array
澳洲射电望远镜阵列上空的行星队列

Credit & Copyright: Graeme L. White & Glen Cozens (James Cook University)
影像提供及版权：Graeme L. White & Glen Cozens (James Cook University)
Explanation: Last week, Mercury, Venus, and the Moon all appeared close together in Earth's sky. This picturesque conjunction was caught on camera behind elements of the Australia Telescope Compact Array (ATCA) near the town of Narrabri in rural New South Wales. The ATCA consists of six radio telescopes in total, each one larger than a house. Together they form one of the highest resolution measurement devices in the world. Impressive planetary conjunctions occur every few years. Involving the brightest objects in the night sky, this alignment was easy to spot just before sunrise. In the picture, taken on the morning of March 6, Mercury is the highest of the three bright celestial beacons.
说明：上周，水星，金星和月球一同紧密地出现在地球的天空中。这张独特的“合”影像是澳洲射电望远镜密集阵（ATCA）后方的相机拍摄，该阵列位于南威尔士纳拉布里郊区附近。ATCA总共有6架射电望远镜，每一架望远镜都比房子大。组合在一起后它们就成为世界上分辨率最高的仪器设备之一。每数年就会发生令人记忆深刻的行星合事件。在这张影像中有夜空中最明亮的天体，在日出前很容易就能看到这个队列。这张影像拍摄于3月6日早晨，水星是三颗天体中位置最高的亮点。

Discover the cosmos! Each day a different image or photograph of our fascinating universe is featured, along with a brief explanation written by a professional astronomer. 2008 March 11

An Avalanche on Mars
火星上发生一次雪崩

Credit: HiRISE, MRO, LPL (U. Arizona), NASA
影像提供：HiRISE, MRO, LPL (U. Arizona), NASA  
Explanation: What caused this sudden cloud of dust on Mars? An avalanche! The first avalanche imaged in progress on another planet was recorded last month on Mars by NASA's robotic Mars Reconnaissance Orbiter. Visible in the above picture, digitally rescaled, are several layers of white ice thawing over red rock, with darker colors toward the right indicated Martian soil that mixed with lesser amounts of ice. As the cliff of over 700 meters high was thawing, falling ice crashed down raising plumes of ice and dust so thick they cast visible shadows. The scarp has slopes with grades greater than 60 degrees. The entire scene is illuminated from the upper right by the Sun. A thaw occurs each spring in the Northern Hemisphere of Mars, as the warming climate causes solid carbon dioxide ice to sublimate directly to vapor. Studying such avalanches allows planetary geologists to better understand soil configurations on Mars.
说明：什么造成了火星上这次突然形成的尘埃云呢？一次雪崩！这是人类首次拍摄到其它行星上雪崩过程，是由NASA的火星勘测卫星在上个月拍摄到的。经过数码调整，在上面的影像中可以看到有数层白色冰雪融化在红色岩石上，朝向右方的深色火星土壤混合了较少量的冰。从700米高的悬崖上融化的冰雪，滑下后经过碰撞，造成了羽状的冰雪以及形成可见阴影的厚厚尘埃。这个悬崖的斜坡角度大于60度。整个过程由上空的太阳照亮。火星北半球每到春天来临都会发生一次解冻，温暖的气候造成了固态的二氧化碳冰直接升华成气体。研究如此的雪崩能让行星地理学家较好地了解火星土壤结构。

Discover the cosmos! Each day a different image or photograph of our fascinating universe is featured, along with a brief explanation written by a professional astronomer.
2008 March 12

Star Forming Region LH 95
恒星形成区域LH 95

Credit: Hubble Heritage Team, D. Gouliermis (MPI Heidelberg) et al., (STScI/AURA), ESA, NASA
影像提供：Hubble Heritage Team, D. Gouliermis (MPI Heidelberg) et al., (STScI/AURA), ESA, NASA  

Explanation: How do stars form? To better understand this complex and chaotic process, astronomers used the Hubble Space Telescope to image in unprecedented detail the star forming region LH 95 in the nearby Large Magellanic Cloud galaxy. Usually only the brightest, bluest, most massive stars in a star forming region are visible, but the above image was taken in such high resolution and in such specific colors that many recently formed stars that are more yellow, more dim, and less massive are also discernable. Also visible in the above scientifically colored image is a blue sheen of diffuse hydrogen gas heated by the young stars, and dark dust created by stars or during supernova explosions. Studying the locations and abundances of lower mass stars in star forming regions and around molecular clouds helps uncover what conditions were present when they formed. LH 95 spans about 150 light years and lies about 160,000 light years away toward the southern constellation of the Swordfish (Dorado).
说明：恒星如何形成？为了更好地了解这个复杂而又混乱的过程，天文学家利用哈勃太空望远镜对大麦哲伦星云附近的恒星形成区域LH95拍摄了空前详细的影像。通常在恒星形成区域中只有最亮，最蓝，质量最大的恒星才能被看到，但在上面这张如此高解析度和特殊色彩的影像中，还能分辨出许多看上去泛黄，暗淡，质量较小的新诞生恒星。在上面这张彩色影像里，还能看到氢气被年轻恒星加热后发出的一片蓝色辉光，以及由恒星或超新星爆炸形成的黑暗尘埃。研究恒星形成区域中大量的低质量恒星和周围分子云能帮助揭开它们形成时的条件。LH95覆盖大约150光年，它位于南方的剑鱼座，距离我们大约16万光年远。

Discover the cosmos! Each day a different image or photograph of our fascinating universe is featured, along with a brief explanation written by a professional astronomer.
2008 March 13

Sculpting the South Pillar
侵蚀中的南部尘埃气柱

Credit: Nathan Smith (Univ. of Colorado), et al., SSC, JPL, Caltech, NASA
影像提供：Nathan Smith (Univ. of Colorado), et al., SSC, JPL, Caltech, NASA

Explanation: Eta Carinae, one of the most massive and unstable stars in the Milky Way Galaxy, has a profound effect on its environment. Found in the the South Pillar region of the Carina Nebula, these fantastic pillars of glowing dust and gas with embedded newborn stars were sculpted by the intense wind and radiation from Eta Carinae and other massive stars. Glowing brightly in planet Earth's southern sky, the expansive Eta Carinae Nebula is a mere 10,000 light-years distant. Still, this remarkable cosmic vista is largely obscured by nebular dust and only revealed here in penetrating infrared light by the Spitzer Space Telescope. Eta Carinae itself is off the top left of the false-color image, with the bright-tipped dust pillars pointing suggestively toward the massive star's position. The Spitzer image spans almost 200 light-years at the distance of Eta Carinae.
说明：船底座η星是银河系中质量最大，最不稳定的恒星之一,它深深地影响着周围的环境。在船底星云南方云气柱区域，发现了这些由炽热尘埃和气体组成的奇异气柱，其中有新诞生的恒星，这些云气柱被船底座η星和其他大质量恒星吹出的强烈恒星风和射线侵蚀。广阔的船底座η星云明亮地闪烁在地球南方天空中，它距离我们大约1万光年。但是，这片美丽的宇宙景色被星云尘埃遮蔽了，只能在斯皮策太空望远镜利用红外光拍摄的影像中看到。船底座η星位于这张假色影像左侧顶部外，明亮的尘埃柱尖指出了这颗大质量恒星的位置。从船底座η星的距离估计，这张斯皮策影像覆盖大约200光年。

Discover the cosmos! Each day a different image or photograph of our fascinating universe is featured, along with a brief explanation written by a professional astronomer.
2008 March 14

Endeavour into the Night
奋进号夜晚升空

Credit: NASA, Jerry Cannon, Rusty Backer
影像提供：NASA, Jerry Cannon, Rusty Backer

Explanation: Blasting into a dark night sky, the Space Shuttle Endeavour began its latest journey to orbit in the early morning hours of March 11. In this stunning picture following the launch, the glare from Endeavour's three main rocket engines and flanking solid fuel booster rockets illuminates the orbiter's tail section and the large, orange external fuel tank. Embarking on mission STS-123, Endeavour left Kennedy Space Center's pad 39A, ferrying a a crew of seven astronauts to the International Space Station (ISS). The cargo included the first section of the Japan Aerospace Exploration Agency's Kibo laboratory and the Canadian Space Agency's two-armed robotic system. Astronauts will conduct a series of space walks to install the new equipment during the 16-day mission, the longest shuttle mission to the ISS.
说明：3月11日凌晨时分，奋进号航天飞机冲破夜空，开始了最近的轨道飞行之旅。在发射后拍摄的这张壮观影像中，奋进号三个主要火箭引擎和航天飞机腹部固体燃料助推火箭喷出的火焰照亮了航天飞机尾部以及那巨大，橘红色的外部燃料箱。为了执行STS-123使命，奋进号飞离了肯尼迪航天中心39A发射台，搭载7名宇航员飞向国际空间站（ISS）。其中装载的货物包括日本宇宙航空探索机构的“希望号”实验舱的第一部分，以及加拿大太空署的两条机械臂系统。在16天的任务时间里，宇航员将进行一系列太空行走来安装新设备，这也是国际空间站时间最长的航天飞机任务。

Discover the cosmos! Each day a different image or photograph of our fascinating universe is featured, along with a brief explanation written by a professional astronomer.
2008 March 17

Thirty Thousand Kilometers Above Enceladus
3万公里上空拍摄到的土卫二

Credit: Cassini Imaging Team, SSI, JPL, ESA, NASA
影像提供：Cassini Imaging Team, SSI, JPL, ESA, NASA

Explanation: What does the surface of Saturn's ice-spewing moon Enceladus look like? To help find out, the robotic Cassini spacecraft now orbiting Saturn was sent soaring past the cryovolcanic moon and even right through one of Enceladus' ice plumes. Cassini closed to about 52 kilometers during its closest encounter to date. The above unprocessed image was taken looking down from the north, from about 30,000 kilometers away. Visible are at least two types of terrain. The first type of terrain has more craters than occur near Enceladus' South Pole. The other type of terrain has few craters but many ridges and grooves that may have been created by surface-shifting tectonic activity. Exogeologists are currently poring over this and other Cassini images from last Wednesday's flyby to better understand the moon's patch-work surface, its unusual ice-geysers, and its potential to support life. Cassini is scheduled to fly by Enceladus at least nine more times, including an even closer pass of just 25 kilometers this coming October.
说明：土星卫星土卫二有冰渗出的表面看起来会是什么样子？为了帮助找到答案，现绕土星飞行的卡西尼飞船，掠过了这颗冰层覆盖了的多火山卫星，甚至拍摄到了土卫二冰雾烟柱之一。在飞越期间，卡西尼飞船距离土卫二表面最近时大约只有52公里。上面这张没有经过处理的影像是从北部向下拍摄的，距离大约有3万公里远。可以看到至少有两种类型的地形。第一种地形是在土卫二南极点附近有许多陨石坑。另一种地形是陨石坑较少，但有许多山脊和凹槽，这可能与地壳运动有关。外太空地质学家们正在查看上周三飞船飞越土卫二时拍摄到的这张以及其它卡西尼影像，以帮助更好的理解该卫星为什么会出现斑纹状地表，奇怪的冰雾喷泉以及可能支持生命存在的潜在可能性。预计，卡西尼飞船还将飞越土卫三二至少9次，还包括今年十月一次更近的飞越，距离土卫二表面仅仅25公里。

Discover the cosmos! Each day a different image or photograph of our fascinating universe is featured, along with a brief explanation written by a professional astronomer.
2008 March 18

M78 and Reflecting Dust Clouds in Orion
猎户座内的M78和反射尘埃云

Credit & Copyright: Martin Pugh
影像提供及版权：Martin Pugh

Explanation: An eerie blue glow and ominous columns of dark dust highlight M78 and other bright reflection nebula in the constellation of Orion. The dark filamentary dust not only absorbs light, but also reflects the light of several bright blue stars that formed recently in the nebula. Of the two reflection nebulas pictured above, the more famous nebula is M78, on the upper right, while NGC 2071 can be seen to its lower left. The same type of scattering that colors the daytime sky further enhances the blue color. M78 is about five light-years across and visible through a small telescope. M78 appears above only as it was 1600 years ago, however, because that is how long it takes light to go from there to here. M78 belongs to the larger Orion Molecular Cloud Complex that contains the Great Nebula in Orion and the Horsehead Nebula.
说明：可怕的蓝色辉光和诡异的尘埃柱，突出了猎户座内M78和另一个明亮的反射星云。黑暗的丝状尘埃不仅仅吸收光，同时还反射数颗明亮蓝色恒星发出的光，而它们刚刚在星云内诞生不久。上面影像中两个反射星云相比，较著名的是位于影像右上角的M78星云，而在它的左下方的则是NGC2071星云。散射光颜色的类型与白天天空出现的蓝光相似，不过是更深的蓝色。M78大小约5光年，可以通过小型望远镜看到它。上面影像中看到的M78是1600年前的景象，因为它发出的光需要经过那么长的时间才能到达地球。M78属于猎户座复杂大分子云的一部分，而猎户座大星云和马头星云也包含在其中。

Discover the cosmos! Each day a different image or photograph of our fascinating universe is featured, along with a brief explanation written by a professional astronomer.
2008 March 19

Mercury in Accentuated Color
颜色加重后的水星

Credit: MESSENGER, NASA, JHU APL, CIW
影像提供：MESSENGER, NASA, JHU APL, CIW

Explanation: The colors of Mercury are subtle but beautiful. At first glance, our Solar System's innermost planet appears simply black and white, but images that include infrared colors normally beyond human vision accentuate a world of detail. One such image, shown above, was acquired by the robotic MESSENGER spacecraft that swung by Mercury in mid-January. Here, most generally, the hot world itself acquires a slightly more brown hue. Many craters that appear on top of other craters -- and so surely have formed more recently -- appear here as bright with bright rays that include a slightly blue tint, indicating that soil upended during the impact was light in color. A few craters, such as some in the huge Caloris Basin impact feature visible on the upper right, appear unexpectedly to be ringed with a dark material, the nature of which is being researched. MESSENGER continues to glide through the inner Solar System and will pass Mercury again this October and next September, before entering orbit around the desolate world in 2011.
说明：水星的颜色较暗但是很漂亮。初乍看，距离太阳最近的行星看上去似乎只是简单的黑白色，但是拍摄到的影像准确地描述了星球的详细信息，其中还包含人类看不到的红外颜色。上面显示的就是这么一张影像，是信使号探测飞船在一月中旬掠过水星时获得的。在这里，最普通的情况下，这颗炽热的星球本身具有微弱的褐色。其中可以看到在许多陨石坑上还有许多陨石坑，可以确定地说上面的陨石坑形成的时间较晚，在这里看上去与明亮的辐射线一样亮，其中还包括一丝蓝色，这表明在碰撞期间，土壤被掀起后露出的浅颜色。比如，影像右上角可以看到一些陨石坑在巨大卡罗维斯低地的碰撞特征，看上去有黑色物质环绕，形成的原因正在研究中。信使号将继续在内太阳系飞行，在今年十月和明年九月将再次通过水星，直至2011年进入绕水星轨道为止。

Discover the cosmos! Each day a different image or photograph of our fascinating universe is featured, along with a brief explanation written by a professional astronomer.
2008 March 20

Sunset: Planet Earth
日落：地球

Credit: Expedition 15 Crew, NASA
影像提供：Expedition 15 Crew, NASA

Explanation: Today, the Sun crosses the celestial equator heading north at 0548 UT. Known as the equinox, the geocentric astronomical event marks the first day of spring in the northern hemisphere and autumn in the south. Equinox means equal night and with the Sun on the celestial equator, Earth dwellers will experience nearly 12 hours of daylight and 12 hours of darkness. Of course, for those in the north, the days will grow longer with the Sun marching higher in the sky as summer approaches. To celebrate the equinox, consider this colorful view of the setting Sun. Recorded last June from the International Space Station, the Sun's limb still peeks above the distant horizon as seen from Earth orbit. Clouds appear in silhouette as the sunlight is reddened by dust in the dense lower atmosphere. Molecules in the more tenuous upper atmosphere are preferentially scattering blue light.  
说明：今天世界时间5点48分，太阳跨过了天球赤道向北运行。今天就是春分，这个地球上的天文事件标志着北半球春天的开始，南半球秋天的来临。春分意味着在夜晚和太阳在天球赤道上的时间相等，地球上的居民将经历12小时的白天与黑夜。当然，对于北半球的人来说，白天会慢慢变长，随着夏天的来临太阳在天空中的位置也会变得更高。为了庆祝春分这个日子，特意将这张美丽的日落影像呈现。该影像是去年6月从国际空间站拍摄，从地球同步轨道上看去，太阳的边缘仍出现在远处地平线上。因低层大气致密的尘埃，太阳光显现红色，云层看上去就像是剪影一样。而上层大气中稀薄的分子更多地是散射蓝光。

Discover the cosmos! Each day a different image or photograph of our fascinating universe is featured, along with a brief explanation written by a professional astronomer.
2008 March 21

Where is HD 189733?
HD189733在哪里？

Image Credit: NASA, ESA, A. Fujii, and Z. Levay (STScI)
影像提供：NASA, ESA, A. Fujii, and Z. Levay (STScI)
Explanation: The star cataloged as HD 189733 is a mere 63 light-years away. Its location is indicated in this deep, wide-angle image of the sky centered on the northern constellation of Cygnus. Considering the many bright stars, nebulae, and star clusters in the region more familiar to skygazers, HD 189733 may not seem to be remarkable, but it is known to have at least one hot, jupiter-sized planet orbiting very close, with an impressively short period of 2.2 days. Because the planet regularly eclipses its parent star, astronomers can study starlight that passes directly through the planet's atmosphere and identify molecules through spectroscopy. Following the discovery of water vapor in the planetary atmosphere, astronomers now report that Hubble Space Telescope data also indicates the signature of methane (CH4). The exciting result is the first detection of an organic molecule on a planet orbiting another star. Although HD 189733's planet is considered too hot and inhospitable to support life, the work is a step toward measuring conditions and chemistry on other extrasolar planets where life could exist.
说明：被编录为HD189733的行星距离我们大约63光年远。它的位置就被标在这张北方天鹅座的深空广角影像中。在这个区域内，天空观测者们更为熟悉许多明亮的恒星，星云和星团，而HD189733可能不是那么显著，但是至少它是一颗炽热，木星大小的行星，轨道非常小，一个周期只需要2.2天时间。因为它规则地掩食母恒星，天文学家能研究恒星发出的光穿过行星大气，分析光谱后确定其中大气内的分子。随着在行星大气中发现了水蒸气后，天文学家现在报告说在哈勃太空望远镜数据中还发现了甲烷的存在。这一令人激动的发现是第一次在围绕另一颗恒星运转的行星上发现了有机分子。尽管HD189733行星非常炽热，不适合生命存在，但这项工作向测试其它太阳系外、可能有生命存在的行星上的条件和化学成分迈出了一步。

Discover the cosmos! Each day a different image or photograph of our fascinating universe is featured, along with a brief explanation written by a professional astronomer.
2008 March 22

Cat's Eye Hubble Remix
哈勃再合成的猫眼

Credit & Copyright: Vicent Peris (OAUV / PTeam), MAST, STScI, AURA, NASA
Explanation: Staring across interstellar space, the alluring Cat's Eye Nebula lies three thousand light-years from Earth. One of the most famous planetary nebulae in the sky, the Cat's Eye (NGC 6543) is over half a light-year across and represents a final, brief yet glorious phase in the life of a sun-like star. This nebula's dying central star may have produced the simple, outer pattern of dusty concentric shells by shrugging off outer layers in a series of regular convulsions. But the formation of the beautiful, more complex inner structures is not well understood. Here, Hubble Space Telescope archival image data has been reprocessed to create another look the cosmic cat's eye. Compared to well-known Hubble pictures, the alternative processing strives to sharpen and improve the visiblility of details in light and dark areas of the nebula and also applies a more complex color palette. Of course, gazing into the Cat's Eye, astronomers may well be seeing the fate of our Sun, destined to enter its own planetary nebula phase of evolution ... in about 5 billion years.

Discover the cosmos! Each day a different image or photograph of our fascinating universe is featured, along with a brief explanation written by a professional astronomer.  
2008 March 23
  
Molecular Cloud Barnard 68
分子云巴纳德68

Credit: FORS Team, 8.2-meter VLT Antu, ESO
Explanation: Where did all the stars go? What used to be considered a hole in the sky is now known to astronomers as a dark molecular cloud. Here, a high concentration of dust and molecular gas absorb practically all the visible light emitted from background stars. The eerily dark surroundings help make the interiors of molecular clouds some of the coldest and most isolated places in the universe. One of the most notable of these dark absorption nebulae is a cloud toward the constellation Ophiuchus known as Barnard 68, pictured above. That no stars are visible in the center indicates that Barnard 68 is relatively nearby, with measurements placing it about 500 light-years away and half a light-year across. It is not known exactly how molecular clouds like Barnard 68 form, but it is known that these clouds are themselves likely places for new stars to form. It is possible to look right through the cloud in infrared light.

Discover the cosmos! Each day a different image or photograph of our fascinating universe is featured, along with a brief explanation written by a professional astronomer.
2008 March 24

Saturn and Titan from Cassini
卡西尼飞船拍摄到的土星和土卫六

Credit: Cassini Imaging Team, SSI, JPL, ESA, NASA
影像提供：Cassini Imaging Team, SSI, JPL, ESA, NASA

Explanation: Spectacular vistas of Saturn and its moon continue to be recorded by the Cassini spacecraft. Launched from Earth in 1997, robotic Cassini entered orbit around Saturn in 2004 and has revolutionized much of humanity's knowledge of Saturn, its expansive and complex rings, and it many old and battered moons. Soon after reaching Saturn, Cassini released the Huygen's probe which landed on Titan, Saturn's largest moon, and send back unprecedented pictures from below Titan's opaque cloud decks. Recent radar images of Titan from Cassini indicate flat regions that are likely lakes of liquid methane, indicating a complex weather system where it likely rains chemicals similar to gasoline. Pictured above, magnificent Saturn and enigmatic Titan were imaged together in true color by Cassini earlier this year.
说明：卡西尼飞船依旧拍摄到了土星及其卫星的壮观影像。1997年从地球发射升空后，卡西尼飞船在2004年进入土星绕行轨道，它让人们对土星的了解发生了翻天覆地的变化，那广阔而复杂的光环，还有许多历尽沧桑的卫星。在到达土星之后，卡西尼飞船立即释放了在土星最大卫星土卫六上着陆的惠更斯探测器，并在土卫六模糊的云盖下拍摄并传回了空前详细的影像。最近，卡西尼飞船利用雷达拍摄到土卫六的影像，其中暗示平坦的区域可能是液态甲烷湖泊，这就说明土卫六上有一个复杂的气候系统，在那里雨的化学成分跟汽油相似。雄伟的土星和谜一般的土卫六一起出现在上面这张卡西尼飞船今年初拍摄的真色彩影像中。

不好意思～～～前一阵忙毕业的事停了好久～～～～
2008 June 6

Two-Armed Spiral Milky Way
两条旋臂的银河系

Illustration Credit: R. Hurt (SSC), JPL-Caltech, NASA
Survey Credit: GLIMPSE
插图提供：R. Hurt (SSC), JPL-Caltech, NASA
测量提供：GLIMPSE
Explanation: Gazing out from within the Milky Way, our own galaxy's true structure is difficult to discern. But an ambitious survey effort with the Spitzer Space Telescope now offers convincing evidence that we live in a large galaxy distinguished by two main spiral arms (the Scutum-Centaurus and Perseus arms) emerging from the ends of a large central bar. In fact, from a vantage point that viewed our galaxy face-on, astronomers in distant galaxies would likely see the Milky Way as a two-armed barred spiral similar to this artist's illustration. Previous investigations have identified a smaller central barred structure and four spiral arms. Astronomers still place the Sun about a third of the way in from the Milky Way's outer edge, in a minor arm called the Orion Spur. To locate the Sun and identify the Milky Way's newly mapped features, just place your cursor over the image.
说明：从银河系内往外看，很难辨认我们银河系的真实结构。但是，斯皮策太空望远镜的巡天计划，提供了一项令人信服的证据，那就是我们处于一个巨大旋涡星系内，其内有两条主要的旋臂（长形盾-半人马臂和英仙臂），出现在巨大的中央旋棒的末端。事实上，如果天文学家从一个有利的位置朝我们银河系观看，那么从遥远星系上看到我们银河系是一个具有两条旋臂的棒旋星系，就像这张艺术家的插图一样。先前的调查确认银河系具有一个较小的中央棒状结构及四条旋臂。天文学家仍然将太阳定位在从银河系外边缘进入内部的1/3位置上，也就是位于被称为猎户座的小旋臂上。为了定位太阳以及确认银河系内出现的新特征，就将你的鼠标上在影像上。

探索宇宙! 每天发布一张有专业天文学家的简短解释和说明的反映我们迷人宇宙的不同影像或照片。
2008 年 06 月 10 日
A Fire Rainbow Over New Jersey
新泽西上空的火彩虹
Credit & Copyright: Paul Gitto (Arcturus Observatory)
影像提供及版权：Paul Gitto (Arcturus Observatory)
Explanation: What is that inverted rainbow in the sky? Sometimes known as a fire rainbow for its flame-like appearance, a circumhorizon arc is created by ice, not fire. For a circumhorizon arc to be visible, the Sun must be at least 58 degrees high in a sky where cirrus clouds are present. Furthermore, the numerous, flat, hexagonal ice-crystals that compose the cirrus cloud must be aligned horizontally to properly refract sunlight like a single gigantic prism. Therefore, circumhorizon arcs are quite unusual to see. Pictured above, however, a rare fire rainbow was captured above trees in Whiting, New Jersey, USA in late May.
说明：天空中那道颠倒的彩虹是什么？通常人们因其类似火焰而称之为火彩虹，日承是由冰晶形成，而不是火焰。这道日承可见的条件是太阳高度必须至少58度，并且高空中一定要有卷云层。而且，形成卷云的数量众多、平坦的六边形冰晶必须在水平方向排列，就像是一面巨大的透镜一样，以恰当的角度折射太阳光。因此，日承很难让人看到。上面的影像是一道罕见的火彩虹，是5月末在美国新泽西州惠延的树林上空拍摄。

探索宇宙! 每天发布一张有专业天文学家的简短解释和说明的反映我们迷人宇宙的不同影像或照片。
2008 年 06 月 11 日
Dextre Robot at Work on the Space Station
国际空间站上工作的Dextre 机器人
Credit: STS-124 Crew, Expedition 17 Crew, NASA
影像提供：STS-124 Crew, Expedition 17 Crew, NASA
Explanation: What's the world's most complex space robot doing up there? Last week, Dextre was imaged moving atop the Destiny Laboratory Module of the International Space Station (ISS), completing tasks prior to the deployment of Japan's Kibo pressurized science laboratory. Dextre, short for the Canadian-built Special Purpose Dextrous Manipulator, has arms three meters in length and can attach power tools as fingers. Behind Dextre is the blackness of space, while Earth looms over Dextre's head. The Kibo laboratory segment being deployed during space shuttle Discovery's trip to the ISS can be pressurized and contains racks of scientific experiment that will be used to explore many things, including how plants brace themselves against gravity, and how water might be inhibited from freezing in cells under microgravity.
说明：世界上最复杂的太空机器人在那里做什么？上个星期， Dextre被拍摄到移动在国际空间站（ISS）命运试验舱的上方，完成了对日本希望号科学实验舱的前期展开任务。Dextre，是加拿大建造的具有特殊用途的灵巧机械臂的简称，整条臂全长三米，能够像手指一样灵活地使用工具。Dextre后方是黑暗的太空，而地球位于Dextre的头顶。希望号试验舱的部分组建在发现号航天飞机此次国际空间站之旅展开的，舱内可以增压，并包含被用来研究许多新事物的科学仪器，其中包括植物如何逆重心生长，以及在微重力状态下细胞内的水分如何抑制凝结。

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2008 年 06 月 12 日

Phoenix and the Snow Queen
凤凰号与冰后
Credit: Kenneth Kremer, Marco Di Lorenzo, Phoenix Mission, NASA, JPL, UA,
Max Planck Inst., Aviation Week and Space Technology
影像提供：Kenneth Kremer, Marco Di Lorenzo, Phoenix Mission, NASA, JPL, UA,
Max Planck Inst., Aviation Week and Space Technology
Explanation: A flat, smooth, shiny feature dubbed the Snow Queen is near the top of this color mosaic of the surface beneath the Phoenix Mars Lander. Recorded with the lander's robotic arm camera as it was maneuvered to look under the lander, the region also includes a leg and plate-sized footpad. An intriguing detail near the footpad at about the 2 o'clock position, is a metal spring partially buried in martian soil, a piece of the arm's now opened biobarrier. The smooth Snow Queen feature is strongly suspected to be ice originally just under the soil, uncovered by the thruster rockets as Phoenix set down on the north polar plains of Mars. In fact, the apparent holes or depressions in the Snow Queen's otherwise flat surface are located just under the thrusters.
说明：在这张凤凰号着陆器下方火星表面的这张彩色影像里，位于顶端附近的那块平坦，光滑，发光的物体被称为冰后。着陆器机械臂上的相机朝下拍摄，这个区域还包括一条支架和餐盘大小的防陷垫。在防陷垫附近大约两点的位置上有一个有趣的细节，一小块金属弹簧部分被埋在火星土壤里，也是机械手臂现已打开的生物屏障的一部分。冰后光滑的特征很明显是在土壤下形成的冰块，当凤凰号飞船降落到火星北极平原时由火箭推进器揭露了其面纱。事实上，冰后平坦表面上的洞穴和凹陷正好位于火箭推进器的下方。

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2008 年 06 月 13 日

At Last, GLAST
GLAST终于升空
Image Credit: Jerry Cannon, Robert Murray, NASA
影像提供：Jerry Cannon, Robert Murray, NASA
Explanation: Rising through a billowing cloud of smoke, this Delta II rocket left Cape Canaveral Air Force Station's launch pad 17-B Wednesday at 12:05 pm EDT. Snug in the payload section was GLAST, the Gamma-ray Large Area Space Telescope, now in orbit around planet Earth. GLAST's detector technology was developed for use in terrestrial particle accelerators. But from orbit, GLAST can study gamma-rays from extreme environments in our own Milky Way galaxy, as well as supermassive black holes at the centers of distant active galaxies, and the sources of powerful gamma-ray bursts. Those cosmic accelerators achieve energies not attainable in earthbound laboratories. GLAST also has the sensitivity to search for signatures of new physics in the r