天文每日一图2005.3.22--3.27

什么是天文每日一图

由NASA (National Aeronautics and Space Administration美国国家航空航天局）在其网站(www.nasa.gov)上提供的每日一幅的天文图片。内容涉及天文学、天体物理、航天技术等方面，并配有专业人士撰写的说明。

网址http://antwrp.gsfc.nasa.gov/apod/astropix.html
精美的图片，展现浩瀚和深邃的宇宙

我和小兔突发奇想翻译这个每日一图，尽量坚持下去，水平有限请各位达人多多指教 ^^

2005.3.22-在空中自由的飞
美国宇航员Bruce McCandless II 打破了前人的纪录，他在离挑战者号（Challenger)航天飞机大约一百米远的地方进行了空中行走。通过使用载人机动装置（Manned Maneuvering Unit ，缩写为MMU)他得以在空中自由的飞翔。

1984年，在一次名为41-B的空间往返任务中，Bruce McCandless II 和另外一名NASA宇航员罗伯特 斯图尔特（Robert Stewart）第一次体验到了无绳空间行走（untethered space walk）的感觉。

载人机动装置（MMN）是靠喷出气体（氮）利用反冲作用提供动力的，它可以用来维修和回收卫星。在地球上它重140千克，但和其他物体一样，在太空中它是失重的。它已在2001年为背包推进装置（SAFER backpack propulsion unit）所取代。（小海译）

To Fly Free in Space
Credit: STS-41B, NASA
Explanation: At about 100 meters from the cargo bay of the space shuttle Challenger, Bruce McCandless II was further out than anyone had ever been before. Guided by a Manned Maneuvering Unit (MMU), astronaut McCandless, pictured above, was floating free in space. McCandless and fellow NASA astronaut Robert Stewart were the first to experience such an "untethered space walk" during Space Shuttle mission 41-B in 1984. The MMU works by shooting jets of nitrogen and has since been used to help deploy and retrieve satellites. With a mass over 140 kilograms, an MMU is heavy on Earth, but, like everything, is weightless when drifting in orbit. The MMU was replaced with the SAFER backpack propulsion unit.

大图http://antwrp.gsfc.nasa.gov/apod ... eflyer_nasa_big.jpg

2005.3.23-火星尘暴

地平线上的白色物体是什么？（箭头所指处）科学家认为那个微小的白色幻影实际上是火星尘暴（Martian dust devil ），也就是扫过火星（Mars.）表面的旋涡。上面的图像由勇气号火星探测器（robotic rover Spirit）在本月早些时候拍摄。它是通过对比同一区域以前的照片发现的。以前也曾发现过火星尘暴刚刚活动过的痕迹（Fresh dust devil tracks），但能看到上图这样接近的情景的确很令人惊奇。在地球上最类似火星尘暴的现象就是龙卷风（tornadoes）和台风（飓风，waterspouts）。火星尘暴产生的最终原因目前仍不清楚，但可以肯定的是它和阳光加热岩石和土壤从而产生的热的上升气流有关。就在这之前，勇气号的电力供应出人意料地增加了，这有可能是尘暴接近或经过火星车时清洁了它的太阳能电池板（solar panels.）的缘故。（小海译注）
注：此处的火星尘暴是小规模的，可称之为小型火星尘暴。

A Dust Devil Swirling on Mars
Credit: Mars Exploration Rover Mission, JPL, NASA
Explanation: What is that wisp on the horizon? Scientists think that the slight white apparition is actually a Martian dust devil that was caught swirling across Mars. The above image was taken earlier this month by the robotic rover Spirit. The swirling cloud was found by comparing the above image to a previous image of the same area. Fresh dust devil tracks have been seen on Mars before, but actually seeing one up close was a surprise. The most similar phenomena to Martian dust devils on Earth are terrestrial dust devils, tornadoes and waterspouts. The ultimate cause of Martian dust devils remains unknown, but might be related to rising air heated by sun-warmed rocks and soil. Just the previous day, Spirit's power acquisition increased unexpectedly, possibly the result of a dust devil passing near or over the Spirit rover and effectively cleaning its solar panels.

2005.3.24-超新星遗迹
这是暗弱的超新星遗迹Simeis 147的清晰影象，如果去追踪图上那些错综复杂的细丝，你很容易会迷失其间。朝金牛座的方向看去，它占据了大约3度的天空大小（相当于6个满月那么大）。这些云气离我们大约有3000光年，所以遗迹的宽度应该约为150光年左右。合成图上的色彩用H的α滤光片曝光了8小时，只吸收那些来自于云气中氢原子与电子复合而发出的光，指引我们探寻那些令人惊叹的生机勃勃的受激气体。看上去这个超新星遗弃的年龄大约有100，000年-意味着这颗巨星爆发的光在十万年前才达到地球。不过这种延展的遗迹并不是巨星爆发的唯一结局，这次的宇宙大灾难同时形成了一颗旋转的中子星，或是脉冲星，这个是巨星核的遗迹。(小兔译)

Simeis 147: Supernova Remnant
Credit & Copyright: Robert Gendler
Explanation: It's easy to get lost following the intricate filaments in this detailed image of faint supernova remnant Simeis 147. Seen towards the constellation Taurus it covers nearly 3 degrees (6 full moons) on the sky corresponding to a width of 150 light-years at the stellar debris cloud's estimated distance of 3,000 light-years. The color composite image includes eight hours of exposure time with an H-alpha filter, transmiting only the light from recombining hydrogen atoms in the expanding nebulosity and tracing the regions of shocked, glowing gas. This supernova remnant has an apparent age of about 100,000 years - meaning light from the massive stellar explosion first reached Earth 100,000 years ago - but this expanding remnant is not the only aftermath. The cosmic catastrophe also left behind a spinning neutron star or pulsar, all that remains of the original star's core.

2005.3.25-惠更斯发现土星的月亮
350年前的今天，即1655年3月25日，荷兰天文学家克里斯蒂安·惠更斯（Christiaan Huygens）发现了一颗土星的卫星，即现在我们所知的土卫六泰坦。为了纪念望远镜中出现的这幅迷人的景象，他所用的仪器都保留了下来。这个仪器是克里斯蒂安·惠更斯 和他兄弟康斯坦丁·惠更斯（Constantijn Huygens)一起设计和建造的。望远镜的透镜的直径只有57毫米（2英寸）沿着镜片边缘刻着"X 3 FEBR. MDCLV"*（位于镜片的下部），意为焦距10 Rhineland feet**(约等于337cm），最后抛光时间是1655年2月3日。它来源于罗马诗人奥维德的诗节"Admovere Oculis Distantia Sidera Nostris".(他们把遥远的星星送到我们眼前)。惠更斯用了颠倒的诗节来宣布他的发现，这种方式在他所处的时代很寻常。惠更斯记下了他的发现却把它当作秘密给保存起来，直到他愿意揭示这个秘密的那一天。解密翻译出来，他的颠倒诗是：“一颗卫星围绕着土星，周期是16天又4个小时。”这与现代探测到的泰坦的轨道周期吻合得很好。(小兔译，小海校注)

注：
* "X 3 FEBR. MDCLV"  ： 罗马数字X=10, 第一个X代表直径是10Rhineland feet；M=1000, D=500, C=100, L=50, V=5 ,罗马数字是右加左减（即在一个较大的罗马数字的右边记上一个较小的罗马数字，表示大数字加小数字），所以MDCLV=1000+500+100+50+5=1655（年）；至于3 FEBR.就是二月三日啦。
**Rhineland feet ：欧洲古代一种长度单位，具体待考。

Huygens Discovers Luna Saturni
Credit & Copyright: Utrecht Univ. Museum, Inst. for History and Foundations of Science
Courtesy: Rob van Gent, Tiemen Cocquyt, and Carl Koppeschaar
Explanation: In 1655, three hundred fifty years ago on this date, Dutch astronomer Christiaan Huygens discovered Luna Saturni - now known as Saturn's moon Titan. To celebrate, consider this intriguing picture of his telescope lens, all that remains of the instrument he used, designed and constructed in collaboration with his brother, Constantijn Huygens. The lens itself measures 57 millimeters (just over 2 inches) in diameter and is inscribed along the border "X 3 FEBR. MDCLV": its focal length (10 Rhineland feet) and the date of its final polishing, 3 February 1655. It also bears a verse from the Roman poet Ovid, "Admovere Oculis Distantia Sidera Nostris" (They brought the distant stars closer to our eyes). Huygens used the verse as part of an anagram announcing his discovery. The use of an anagram, a practice common in his time, established a date for his discovery but kept its details secret until he wished to reveal them. Decoded and translated, his anagram reads "A moon revolves around Saturn in 16 days and 4 hours.", a good agreement with the modern value for Titan's orbital period.

看大图http://antwrp.gsfc.nasa.gov/apod/image/0503/huygens_lens_f1.jpg

2005.3.26-蟹状星云合成图
这张照片是著名的蟹状星云（Crab Nebula）中心部分的合成图像，一颗城市大小的、每秒旋转30次的磁中子星---蟹状星云脉冲星位于该图的中心。这张壮观的图像合成了来自哈勃太空望远镜（Hubble Space Telescope）的光学图像（红）和来自钱德拉卫星（ Chandra Observatory）的X射线图像（蓝），这也曾被用于广为流传的蟹状星云动画（Crab Pulsar movies）中。脉冲星就像一部宇宙发电机，从核心发射X射线和光学辐射，加速带电粒子产生奇异的炽热的X射线喷流。像环一样的结构是X射线发射区，在这里高能粒子猛烈撞击星云物质。最里面的环大约有一光年左右。中心的脉冲星是由大质量恒星塌缩形成的，它的质量比太阳要大而密度和原子核差不多，而星云则是由恒星外层膨胀所形成的。这颗超新星的爆发在1054年*被人们观测到. （小海译注，小兔校）
*北宋至和元年

Composite Crab
Credit: J. Hester (ASU) et al., CXC, HST, NASA
Explanation: The Crab Pulsar, a city-sized, magnetized neutron star spinning 30 times a second, lies at the center of this composite image of the inner region of the well-known Crab Nebula. The spectacular picture combines optical data (red) from the Hubble Space Telescope and x-ray images (blue) from the Chandra Observatory, also used in the popular Crab Pulsar movies. Like a cosmic dynamo the pulsar powers the x-ray and optical emission from the nebula, accelerating charged particles and producing the eerie, glowing x-ray jets. Ring-like structures are x-ray emitting regions where the high energy particles slam into the nebular material. The innermost ring is about a light-year across. With more mass than the Sun and the density of an atomic nucleus, the spinning pulsar is the collapsed core of a massive star that exploded, while the nebula is the expanding remnant of the star's outer layers. The supernova explosion was witnessed in the year 1054.

2005.3.27-爱因斯坦十字
大多数的星系都只有一个核，为什么上图这个星系有4个呢？这实在是很奇怪，所以天文学家们只能认为在这张图里其实是看不见这个星系的核的。中间的苜蓿状的天体实际上是后面的一颗类星体（quasar）发出的。前景星系的巨大引力场使这颗遥远的类星体发出的星光被弯曲成四个不同的影像。要发生这种幻象，这颗类星体必须在一个巨大星系中心的正后方。这种效应统称为引力透镜（gravitational lensing），而图上这种特殊的例子称为爱因斯坦十字（Einstein Cross）。更有趣的是，爱因斯坦十字的图像亮度会改变。因为有时候，前景星系中会有一些特殊恒星产生额外的微引力透镜效应（gravitational microlensing ），这种效应会使亮度变大。（小兔译，小海校）

The Einstein Cross Gravitational Lens
Credit & Copyright: J. Rhoads (STScI) et al., WIYN, AURA, NOAO, NSF
Explanation: Most galaxies have a single nucleus -- does this galaxy have four? The strange answer leads astronomers to conclude that the nucleus of the surrounding galaxy is not even visible in this image. The central cloverleaf is rather light emitted from a background quasar. The gravitational field of the visible foreground galaxy breaks light from this distant quasar into four distinct images. The quasar must be properly aligned behind the center of a massive galaxy for a mirage like this to be evident. The general effect is known as gravitational lensing, and this specific case is known as the Einstein Cross. Stranger still, the images of the Einstein Cross vary in relative brightness, enhanced occasionally by the additional gravitational microlensing effect of specific stars in the foreground galaxy.

真棒！！！ ^^

支持！！！！！

每日一图的确经典
我从去年底开始陆续做了几期
因为各种事务繁忙而多次中断
参见下面的帖子
http://www.astronomy.com.cn/bbs/viewtopic.php?t=31417

现在APOD的正式中文版有两个
一是台湾成大物理分站
一是刚刚成立的北京天文馆分站
成大物理分站做得比较久了
而且坚持每天更新
基本上能与NASA保持同步

既然我们也要做
就应该做得更好
不仅仅是在翻译上下功夫
做到信、达、雅
在格式上也应该规范化
尽量保持与NASA原版一致
包括其中的各种链接也不能给省略掉

我很期望能把APOD牧夫分站这个责任交给你
加油！
小海
还有小兔

前辈的好图，顶顶