天文每日一图2005.3.28--3.31

2005.3.28-太空套索
这条套索是外太空最伟大的传奇之一。套索（Tethers），是一段长长的绳子，能帮助稳定卫星轨道，产生电力和方便传输。也许关于太空套索最极端的想法是科幻作家Arthur C. Clarke提出的著名的太空电梯，那是一个用来连接地面和地球同步轨道（geosynchronous orbit）的套索。套索的一个大问题是它的强度，很难建造一根足够长的又不会断裂的可用绳索。为了发挥太空套索的巨大潜力，NASA和太空漫步基金会（SpaceWard Foundation）共同提出了百年套索挑战计划，为最好的太空套索提供一笔资金奖励。当然这个最好的太空套索至少要超过一定的限制。图上展示的是亚特兰蒂斯号太空船（space shuttle Altantis ）1992年部署套索卫星1（Tethered Satellite System 1 ，TSS-1）的景象。和其他的探索性套索一样，TSS-1没能达到限制的标准，但是我们仍然从中得到了很多宝贵的经验。(小兔译)

A Tether in Space
Credit: TSS-1, STS-46 Crew, NASA
Explanation: One of the greatest unrequited legends of outer space is the tether. Tethers, long strands of material, hold the promise of stabilizing satellites, generating electricity, and allowing easy transportation. Possibly the most extreme vision of the space tether is the space elevator popularized by Arthur C. Clarke, where a tether is constructed that connects the ground to geosynchronous orbit. One problem is strength - it is difficult to make a long useful tether that does not snap. To help realize more of the tremendous potential of space tethers, NASA and the SpaceWard Foundation have issued the Centennial Tether Challenge, promising a monetary reward for the best space tether that exceeds a minimum standard. Pictured above is the deployment of the Tethered Satellite System 1 (TSS-1) by the space shuttle Altantis in 1992. Like other tested tethers, TSS-1 failed to live up to its promise, although many valuable lessons were learned.

2005.3.29-新月状的泰坦和戴奥妮
试想一下有好几个月亮的天空将是什么样的呢？土星（Saturn）上就有这样的天空。当土星的卫星彼此靠近时，它们就会处于相似的相位（phase）。这张土星的两个最著名的卫星处于峨嵋月相时的照片是由环绕土星运行的卡西尼号（Cassini）无人飞船在上个月拍到的。泰坦（Titan）位于该图的左下方，是太阳系最大的卫星之一，终年为云层所覆盖。不久前，惠更斯探测器在泰坦上着陆，第一次为人类描绘了它那奇特的表面，戴奥妮（Dione）在图的右上角，它的直径还不及泰坦直径的四分之一，也没有显著的大气。戴奥妮虽然看起来比较小，但飞船在拍摄时离它的距离实际上只有泰坦的一半。（小海译，小兔校）

Crescents of Titan and Dione
Credit: Cassini Imaging Team, SSI, JPL, ESA, NASA
Explanation: What would it be like to see a sky with many moons? Such is the sky above Saturn. When appearing close to each other, moons will show a similar phase. A view with two of the more famous moons of Saturn in crescent phase was captured last month by the robot spacecraft Cassini now orbiting Saturn. Titan, on the lower left, is among the largest moons in the Solar System and is perpetually shrouded in clouds. Recently, the Huygens probe landed on Titan and gave humanity its first view of its unusual surface. Dione, on the upper right, has less than a quarter of Titan's diameter and has no significant atmosphere. Dione, although appearing smaller, was only half the distance to Titan when the above image was taken.

2005.3.30-M74中的超亮X射线源
正如我们所见，M74是一个几乎正面朝向我们的旋涡星系，它位于双鱼座方向，距离我们约3000万光年。上面这幅合成图中的红色斑点是由钱德拉（Chandra）X射线天文台绘制的超亮X射线源（ULXs）。超亮X射线源得名于它们居然比通常的X射线双星（x-ray binary stars）要亮上10到1000倍，这些X射线双星中隐藏着中子星或恒星质量的黑洞（stellar mass black hole）。观测表明，这些超亮X射线源的X射线光变周期大约为2小时左右，因此，天文学家们推测超亮X射线源应该是中等质量的黑洞（约为10000个太阳质量）。这些黑洞还是比潜伏在大的旋涡星系中的百万个太阳质量的大黑洞要小得多了。这些中等质量的黑洞是怎么会在那里呢？一种很有趣的想法是，它们是被旋涡星系M74所吞并的一些小星系的核。（小兔小海合译，小海校）

ULXs in M74
Credit: X-ray; J. Liu (U.Mich.) et al., CXC, NASA - Optical; T. Boroson (NOAO), AURA, NOAO, NSF
Explanation: In visual appearance, M74 is a nearly perfect face-on spiral galaxy, about 30 million light-years away toward the constellation Pisces. The red blotches seen in this composite view are ultraluminous x-ray sources (ULXs) mapped by the Chandra X-ray Observatory. The ULXs are so called because they actually do radiate 10 to 1,000 times more x-ray power than "ordinary" x-ray binary stars, which harbor a neutron star or stellar mass black hole. In fact, watching these ULXs change their x-ray brightness over periods of 2 hours or so, astronomers conclude that ULXs could well be intermediate mass black holes -- black holes with masses 10,000 times or so greater than the Sun, but still much less than the million solar mass black holes which lurk in the centers of large spiral galaxies. How did these intermediate mass black holes get there? One intriguing suggestion is that they are left over from the cores of much smaller galaxies that are merging with spiral galaxy M74.

2005.3.31-地球的伽马射线像

这颗由像斑构成的行星竟然是我们的地球的伽马射线（gamma rays）像，伽马射线是各种电磁波中能量最高的一种辐射。事实上，产生这幅图像的伽马射线的能量超过3500万电子伏（electron volts，35Mev）,而一个典型的可见光光子的能量只有两个电子伏。地球的伽马射线辉光（gamma-ray glow ）非常微弱，所以这张图综合了7年的观测数据才得以成象，花费了康普顿X射线天文台（Compton Gamma Ray Observatory）在地球轨道上工作的时候（1991-2000）的所有对地观测时间来曝光。图中边缘最亮而中心较暗，表明伽马射线来自地球的高层大气。伽马射线产生于大气和来自太空的宇宙线（cosmic rays）的相互作用，大气阻止了伽马射线这种有害的辐射到达地球表面。天文学家需要知道地球的伽马射线辉光的情况，因为它会妨碍宇宙伽马射线源（cosmic gamma-ray sources）的观测，宇宙伽马射线源如脉冲星、超新星遗迹（supernova remnants）以及由超大质量黑洞（supermassive black holes）提供能量的遥远的活动星系等等。（小海译，小兔校）

Gamma-Ray Earth
Credit: Dirk Petry (GLAST Science Support Center), EUD, EGRET, NASA
Explanation: The pixelated planet above is actually our own planet Earth seen in gamma rays - the most energetic form of light. In fact, the gamma rays used to construct this view pack over 35 million electron volts (MeV) compared to a mere two electron volts (eV) for a typical visible light photon. The Earth's gamma-ray glow is indeed very faint, and this image was constructed by combining data from seven years of exposure during the life of the Compton Gamma Ray Observatory, operating in Earth orbit from 1991 to 2000. Brightest near the edge and faint near the center, the picture indicates that the gamma rays are coming from high in Earth's atmosphere. The gamma rays are produced as the atmosphere interacts with high energy cosmic rays from space, blocking the harmful radiation from reaching the surface. Astronomers need to understand Earth's gamma-ray glow well as it can interfere with observations of cosmic gamma-ray sources like pulsars, supernova remnants, and distant active galaxies powered by supermassive black holes.

刚刚发现天文每日一图已经有了简体中文版了，是由北京天文馆翻译的
网址是http://www.bjp.org.cn/apod/today.htm

另外还有台湾成功大学物理系的繁体中文版，网址为（常常更新得比英文主页还快，真是奇怪）http://www.phys.ncku.edu.tw/~astrolab/mirrors/apod/apod.html

北京师范大学天文系主页上也有镜像（英文）http://astro.bnu.edu.cn/apod/lib/aptree.html

主站http://antwrp.gsfc.nasa.gov/apod/astropix.html

图好，文也好。。。。。学习。。。。。。 ^^

成大有时会出点小错，比如漏掉一个‘万‘什么的，不过文笔不错，功力深厚 ^^ ，而且更新极快（似乎有时比英文主站还快），至于译名差异也是可以接受的，人家那种译法也有它的道理嘛

小海，我当你的坚强后盾~~~~~：P

这样发图好象有点不方便，楼主可不可以做个索引呢^0^

正经点说话了哈，不好意思：）
这个本来是小海和我做着玩的，因为当是还没看到有简体中文的翻译。到目前为止我们坚持了10天左右。当然现在有天文馆的翻译了：）
这样我们本来就可以不做了，但又觉得实在很好玩，每天都充满了期待，还有点成就感在里面哈~~
如果有可能的话，发掘更多新鲜的东东和大家共享^0^