APOD：M31集锦

在开始M31的哈勃专题之前，今天先发历年来APOD（天文每日一图）中已经发过的M31集锦。早期的APOD图像太小了，如果没有大的价值，这些图将被过滤。翻译文章参考了成大、北京天文馆的原始翻译，修正了部分纰漏。
论坛中有另一个M31专题，看这个链接：
http://www.astronomy.com.cn/bbs/viewthread.php?tid=72655

先要说明一下，哈勃的图像分辨率确实很高，但相伴的另一特点是视场很小，M31这么大的范围显然不能包含在一个哈勃单图上。ACS拍摄了大量M31的图像，相关的FITS数据实在多了些，具体参考下面这个链接的8楼始：
http://www.astronomy.com.cn/bbs/thread-126842-1-1.html，其中说明：仅仅下载4个归一化文件对应的FITS，就有5.4GB的压缩文件！

这个链接可以下载第2代数字巡天项目（DSS2）中拍摄的M31附近天区的FITS文件，大家可以自己合成彩图：
http://www.spacetelescope.org/projects/fits_liberator/m31data.html

下面显示了合成后的彩图：

                               
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http://antwrp.gsfc.nasa.gov/apod/ap951231.html

December 31, 1995
The X-ray Sources of M31
1995.12.31：M31中的X线源

                               
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Credit: ROSAT, MPE, NASA
版权：美国宇航局（NASA），德国马克斯—普朗克研究院物理研究所（MPE），伦琴X线天文卫星（ROSAT）
Explanation:
Just like our own Milky Way Galaxy, the nearest major galaxy M31 has many star systems spewing high energy radiation. High energy X-radiation  is visible to certain satellites in Earth orbit such as ROSAT  - which took the above picture. The X-ray sources in M31 occur in globular clusters, the spiral arms, and near the galaxy's center. Probably most of these sources are accretion disk binary star systems. M31 has more X-ray sources near its center than our Galaxy, and the reason for this is currently unknown.
解说：与我们的银河系类似，最近的巨型星系——仙女座大星系M31含有大量发射高能辐射的恒星系统。高能X线辐射能被地球轨道上的X射线卫星看见——比如ROSAT，它拍摄的M31图像如上所示。其中的X线源位于：球状星团、旋臂、星系核附近。估计大部分的X线源来自双星系统的吸积盘。M31核心附近有大量的X线源，远多于银心，原因尚不清楚。

http://antwrp.gsfc.nasa.gov/apod/ap991114.html

November 14, 1999
M31: The Andromeda Galaxy
1999.11.14：仙女座大星系M31

                               
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Credit & Copyright: Jason Ware
版权、拍摄：Jason Ware
Explanation:
Andromeda is the nearest major galaxy to our own Milky Way Galaxy. Our Galaxy is thought to look much like Andromeda. Together these two galaxies dominate the Local Group of galaxies. The diffuse light from Andromeda  is caused by the hundreds of billions of stars that compose it. The several distinct stars that surround Andromeda's image are actually stars in our Galaxy that are well in front of the background object. Andromeda is frequently referred to as M31 since it is the 31st object on Messier's list of diffuse sky objects. M31 is so distant it takes about two million years for light to reach us from there. Much about M31 remains unknown, including why the center contains two nuclei.
仙女座大星系M31是离我们最近的大型星系。一般认为，我们的银河系与仙女座大星系很相似，它们两者在本星系群中处于支配地位。M31撒播的光来自其中的数千亿颗恒星，而图像中M31周围的大量明亮群星是我们银河系中该方向的前景星。M31的名称来自它是梅西耶弥漫天体表中的第31#，它相当“遥远”，来自它的星光需要200万年以上才能到达我们这里。M31中还有大量未解之谜，包括它为何有2个核心。
PS：相关哈勃内容明天发——gohomeman1注

http://antwrp.gsfc.nasa.gov/apod/ap000121.html

2000 January 21
X For Andromeda
2000.1.21：M31核心的X线照片

                               
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Credit: S. Murray,M. Garcia,et al.,(CfA)SAO,CXO,NASA
版权：美国宇航局（NASA），哈佛—史密松天体物理中心（CfA），史密松天体物理观测台（SAO），哈佛钱德拉X线卫星官网（CXO），两位科学家及其团队
Explanation:
A big beautiful spiral galaxy 2 million light-years away,Andromeda (M31)has long been touted as an analog to the Milky Way,a distant mirror of our own galaxy.The popular 1960s British sci-fi series,A For Andromeda,even postulated that it was home to another technological civilization that communicated with us.Using the newly unleashed observing power of the orbiting Chandra X-ray telescope,astronomers have now imaged the center of our near-twin island universe, finding evidence for an object so bizarre it would have impressed many 60s science fiction writers (and readers).
仙女座大星系M31是个美丽的大型涡旋星系，离我们约200万光年。长期以来，我们认为它与银河系很相似，是其遥远的镜像。英国20世纪60年代的科幻小说《仙女座来客》中，甚至设定M31是另一个能与我们通讯的高科技文明发源地。借助新近发射的强大的空间望远镜——钱德拉X线卫星，天文学家获得了离我们很近的这个孪生星系核心的清晰图像，其中新发现的天体说不定会让60年代的作者和读者又大吃一惊。
Like the Milky Way, Andromeda's galactic center appears to harbor an X-ray source characteristic of a black hole of a million or more solar masses.Seen above,the false-color X-ray picture shows a number of X-ray sources, likely X-ray binary stars, within Andromeda's central region as yellowish dots.The blue source located right at the galaxy's center is coincident with the position of the suspected massive black hole.While the X-rays are produced as material falls into the black hole and heats up, estimates from the X-ray data show Andromeda's central source to be surprisingly cool - only a million degrees or so compared to the tens of millions of degrees indicated for Andromeda's X-ray binaries.
与我们的银河系类似，仙女座大星系的核心区的X线特征表明：那里隐藏着质量超过数百万太阳的超级黑洞。如上面的伪彩图所示，M31的核心区有许多貌似X线双星的源，图中以黄色点表示。图中的蓝点源正好位于星系核心，与推测的超级黑洞位置重合。基于X线是物质落入黑洞期间被加热而辐射出的，观测数据表明，这个中心源的温度大大低于预期——仅有数百万度~上千万度，与X线双星系统的典型温度很接近。

http://antwrp.gsfc.nasa.gov/apod/ap000908.html

2000 September 8
Andromeda Island Universe
2000.9.8：宇宙岛——M31

                               
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Credit & Copyright: Robert Gendler
拍摄者、版权：（著名天文摄影大师）Robert Gendler
Explanation:
How far can you see? The most distant object easily visible to the unaided eye is M31, the great Andromeda Galaxy some two million light-years away. Without a telescope, even this immense spiral galaxy appears as an unremarkable, faint, nebulous cloud in the constellation Andromeda.
我们能看到多远？肉眼可见的最遥远天体是M31——离我们约200万光年的巨大的仙女座大星系。不借助望远镜，这个庞大的涡旋星系不过是仙女座内不起眼的昏暗云团而已。
But a bright yellow nucleus, dark winding dustlanes, gorgeous blue spiral arms and star clusters are recorded in this stunning telescopic digital mosaic of the nearby island universe. While even casual skygazers are now inspired by the knowledge that there are many distant galaxies like M31, astronomers seriously debated this fundamental concept only 80 years ago. Were these "spiral nebulae" simply outlying components of our own Milky Way Galaxy or were they instead "island universes" -- distant systems of stars comparable to the Milky Way itself? This question was central to the famous Shapley-Curtis debate of 1920, which was later resolved by observations of M31 in favor of Andromeda, island universe.
但在这张近邻宇宙岛漂亮的数码拼接图像中，可以清晰看到明亮的黄色核心、蜿蜒的黑色尘埃带、灿烂的蓝色旋臂和星团。虽然现在观星新手也知道，宇宙中有无数与M31类似的遥远星系；但是80年前，这样的基本概念在天文学界却争议极大：这些“螺旋型星云”到底是我们银河系外围的偏僻天体，还是它们与银河系一样，是遥远的“宇宙岛”？1920年，就此问题进行了著名的Shapley-Curtis辩论。后来一系列的观测表明，M31是遥远的“宇宙岛”。

http://antwrp.gsfc.nasa.gov/apod/ap010917.html

2001 September 17
Southwest Andromeda
2001.9.17：仙女座大星系的西南区域

                               
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Credit & Copyright: Satoshi Miyazaki (NAOJ) et al., Suprime-Cam, Subaru Telescope, NOAJ
版权：日本国家光学天文台（NOAJ）、宫崎聪志团队，昴星团（斯巴鲁）望远镜及其上的超级相机（蓝、绿和H-α滤镜）
Explanation:
This new image composite of the southwest region of M31 from the Subaru Telescope shows many stars, nebulae, and star clusters never before resolved. An older population of stars near Andromeda's center causes the yellow hue visible on the upper right. Young blue stars stand out in the spiral arms on the lower left. Red emission nebula, blue open clusters of stars, and sweeping lanes of dark dust punctuate the swirling giant. Andromeda, at about 2.5 million light years distant, and our Milky Way are the largest galaxies in the Local Group of Galaxies. Understanding M31 helps astronomers to understand our own Milky Way Galaxy, since the two are so similar.
这张新公布的昴星团（斯巴鲁）望远镜拍摄的M31组合图像，显示了以前未解析清楚的许多恒星、星云和星团。图的左上，大量老年恒星构成了星系发黄的核心区；年轻蓝星组成了右下的旋臂主体。巨大的涡旋星盘上，点缀着红色的发射星云、蓝色的疏散星团和弯弯曲曲的尘埃带。仙女座大星系离我们约250万光年，和我们银河系一起，是本星系群中最大的2个星系。由于两者很相似，研究M31有助于天文学家更多地了解银河系。

http://antwrp.gsfc.nasa.gov/apod/ap020518.html

2002.5.18的内容、图像完全是copy了6#楼2000.9.8的，APOD常常炒冷饭的，后面估计还有。

http://antwrp.gsfc.nasa.gov/apod/ap021021.html
2002 October 21
M31: The Andromeda Galaxy  
2002.10.21：仙女座大星系M31

                               
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Credit & Copyright: Robert Gendler
拍摄者、版权：Robert Gendler
Explanation:  
Andromeda is the nearest major galaxy to our own Milky Way Galaxy. Our Galaxy is thought to look much like Andromeda. Together these two galaxies dominate the Local Group of galaxies. The diffuse light from Andromeda is caused by the hundreds of billions of stars  that compose it. The several distinct stars that surround Andromeda's image are actually stars in our Galaxy that are well in front of the background object. Andromeda  is frequently referred to as M31 since it is the 31st object on Messier's list of diffuse sky objects. M31 is so distant it takes about two million years for light to reach us from there. Although visible without aid, the above image  of M31 is a digital mosaic of 20 frames taken with a small telescope. Much about M31 remains unknown, including how the center acquired two nuclei.
仙女座大星系M31是离我们最近的大型星系。一般认为，我们的银河系与仙女座大星系很相似，它们两者在本星系群中处于支配地位。M31撒播的光来自其中的数千亿颗恒星，而图像中M31周围的大量明亮群星是我们银河系中该方向的前景星。M31的名称来自它是梅西耶弥漫天体表中的第31#，它相当“遥远”，来自它的星光需要200万年以上才能到达我们这里。M31中还有大量未解之谜，包括它为何有2个核心。
PS：本文显然与4#楼一样，不同的仅是图——gohomeman1注

http://antwrp.gsfc.nasa.gov/apod/ap031222.html
2003 December 22
The Andromeda Galaxy from GALEX  
2003.12.22：星系演化探测卫星（GALEX）拍摄的M31

                               
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Credit: GALEX team, Caltech, NASA
版权：美国宇航局（NASA），加州理工学院，GALEX团队
Explanation:
Why does the Andromeda Galaxy have a giant ring? Viewed in ultraviolet light, the closest major galaxy to our Milky Way Galaxy looks more like a ring galaxy  than a spiral. The ring is highlighted beautifully in this newly released image mosaic of Andromeda (M31) taken by the GALaxy Evolution Explorer (GALEX), a satellite launched into Earth orbit in April. In the above image, ultraviolet colors have been digitally shifted to the visual. Young blue stars dominate the image, indicating the star forming ring as well as other star forming regions even further from the galactic center. The origin of the huge 150,000-light year ring is unknown but likely related to gravitational interactions with small satellite galaxies that orbit near the galactic giant. M31 lies about three million light-years distant and is bright enough to be seen without binoculars toward the constellation  of Andromeda.
为何仙女座大星系（M31）有个巨型的环状结构？这个离银河系最近的巨型星系，在紫外光图像中看来更像环状星系，而不太像涡旋星系。在这张新公布的星系演化探测卫星（GALEX）拍摄的M31拼接图中，巨环显得分外美丽。GALEX于当年4月发射升空。上图中，紫外光图像已经采用数字技术，配色为可见光图像。图中最显著的是大量年轻蓝巨星组成的星环，和其他恒星形成区域一样远离星系中心。直径15万光年的庞大巨环的起因尚不清楚，推测与环绕巨星系M31的那些伴星系的引力扰动有关。M31离我们约300万光年，它是如此明亮以致于我们无需双筒望远镜，就能在仙女座方向直接看到它。

http://antwrp.gsfc.nasa.gov/apod/ap040718.html

2004.7.18的内容、图像完全是copy了9#楼2002.10.21的，APOD炒冷饭立刻兑现。

http://antwrp.gsfc.nasa.gov/apod/ap041227.html
2004 December 27
Andromeda's Core   
2004.12.27：仙女座大星系的核心

                               
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Credit & Copyright:  Robert Gendler
拍摄者、版权：Robert Gendler
Explanation:
The center of the Andromeda galaxy is beautiful but strange. Andromeda, indexed as M31, is so close to our own Milky Way Galaxy that it gives a unique perspective into galaxy composition by allowing us to see into its core. Billions of stars swarm around a center that has two nuclei and likely houses a supermassive black hole over 5 million times the mass of our Sun. M31 is about two million light years away and visible with the unaided eye towards the constellation  of Andromeda, the princess. Pictured above, dark knots of dust are seen superposed on the inner 10,000 light years of M31's core. The brighter stars are foreground stars located in our Milky Way Galaxy.
仙女座大星系(M31)的核心相当美丽但也很奇异。M31离我们银河系是如此之近，以致于它提供了独一无二的视角让我们通过仔细观测其核心的方法研究星系的组成。数十亿颗恒星蜂拥在2个核心周围，貌似其中还有一个500万太阳质量以上的超级黑洞。M31位于仙女座，离我们约200万光年，用肉眼直接可见。上图中，黑暗的尘埃团块叠加在1万光年直径的M31核心前方，而星系周围的明亮恒星是我们银河系中的前景星。

http://antwrp.gsfc.nasa.gov/apod/ap051020.html
2005 October 20
The Andromeda Galaxy in Infrared    
2005.10.20：仙女座大星系的红外光图像

                               
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Credit : K. Gordon (U. Arizona), JPL-Caltech, NASA
版权：美国宇航局（NASA），加州理工学院，喷气推进实验室（JPL），K.戈登（亚利桑那大学）
Explanation:
What is the Andromeda galaxy really like? To find out, astronomers looked at our largest galactic neighbor in a different light: infrared. Astronomers  trained the orbiting Spitzer Space Telescope at the Messier monster (M31) for over 18 hours, creating a mosaic that incorporated 11,000 separate exposures. The result, pictured above, shows M31 in greater infrared detail than ever before. Infrared light in this 24-micron color band is particularly sensitive to dust heated up by stars. Visible above are previously undiscovered features including intricate structure in the spiral arms, a spiral arc near the center, an off center ring of star formation, and an unusual hole in the galaxy's disk. In contrast, the Andromeda galaxy appears much smoother in visible light and even ultraviolet light. Analyses and comparison of this image to other images will likely yield clues not only to the violent past of M31 but to our own Milky Way Galaxy as well.
仙女座大星系（M31）的真实外观怎样的？为了获取答案，天文学家使用不同的波段——红外线观测我们最大的邻近星系。天文学家使用斯皮策空间望远镜拍摄庞大的M31超过18个小时，构建了这张由1.1万张单独曝光图像组成的合成图。如上所示的图中，显示了M31前所未见的大量红外细节。拍摄所用的24微米波段，是尘埃微粒被恒星加热后辐射的敏感波段。上图中，以前未发现的细节包括：结构复杂的旋臂、核心附近的弧形臂，远离核心的恒星诞生环，以及星盘上不寻常的空洞区。相比之下，在可见光甚至紫外线波段，M31旋臂就显得光滑得多。分析比较这些影像，不但能获得M31狂暴过去的线索，还能了解我们银河系的过去。

上图的高清版本下载
MIPS的24微米版本：
http://ipac.jpl.nasa.gov/media_images/ssc2005-20a1.tif，8193x2410，大小未知

http://ipac.jpl.nasa.gov/media_images/ssc2005-20a1.jpg，同上，21.1MB

MIPS的24、70、160微米红外波段合成图像
http://ipac.jpl.nasa.gov/media_images/ssc2005-20a2_mac.tif，2071x609，1.3MB

http://ipac.jpl.nasa.gov/media_images/ssc2005-20a2.jpg，同上，507KB

图文并茂，是一篇了解M31的好帖子。

http://antwrp.gsfc.nasa.gov/apod/ap051222.html
2005 December 22
Andromeda Island Universe
2005.12.22：仙女座岛宇宙

                               
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Credit & Copyright: Robert Gendler
拍摄者、版权：Robert Gendler
Explanation:
The most distant object easily visible to the unaided eye is M31, the great Andromeda Galaxy some two million light-years away. But without a telescope, even this immense spiral galaxy - spanning over 200,000 light years - appears as a faint, nebulous cloud in the constellation Andromeda. In contrast, a bright yellow nucleus, dark winding dust lanes, gorgeous blue spiral arms and star clusters are recorded in this stunning telescopic digital mosaic with a cumulative exposure of over 90 hours. While even casual skygazers are now inspired by the knowledge that there are many distant galaxies like M31, astronomers seriously debated this fundamental concept only 80 years ago. Were these "spiral nebulae" simply outlying components of our own Milky Way Galaxy or were they instead "island universes" -- distant systems of stars comparable to the Milky Way itself? This question was central to the famous Shapley-Curtis debate of 1920, which was later resolved by observations  of M31 in favor of Andromeda, island universe.
说明:肉眼能够看到最远的天体是M31，即著名的仙女座星系，它距离地球约有200多万光年。不过不借助望远镜，就算是这个巨大的螺旋星系-横跨20多万光年，但看起来只是仙女座内一团不显眼的暗淡云气而已。不同的是，上图望远镜拍摄的累计曝光超过90小时的数字合成影像中，可以清楚看到明亮的黄色星核、黝黑蜿蜒的尘埃带和壮丽的蓝色旋臂与星团。虽然现在连刚入门的观星者都知道，宇宙有许多像M31这样的星系，不过在短短的80年前，天文学界连这种简单的观念都存在非常大的争论。论战的重点在于这种螺旋星系是我们银河外围的天体，或者它们是"岛宇宙"，一些和我们银河系同等地位的星系呢？而1920年Shapley-Curtis之间著名的公开辩论，主要的目的就是要解决上述的议题。后来一系列针对M31的观测，证实了仙女座大星系的确是个岛宇宙。（翻译：陈昌）
PS：本文与6#楼非常像，翻译是北京天文馆的，直接copy了——gohomeman1注

http://antwrp.gsfc.nasa.gov/apod/ap060609.html
2006 June 9
Infrared Andromeda  
2006.6.9：仙女座大星系的红外图像

                               
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Credit: Pauline Barmby(Harvard-Smithsonian CfA)et al.,JPL, Caltech, NASA
版权：美国宇航局（NASA），加州理工学院，喷气推进实验室（JPL），哈佛—史密松天体物理中心（CfA）Pauline Barmby（女）团队
Explanation:
This wide, detailed Spitzer Space Telescope view features infrared light from dust (red) and old stars (blue) in Andromeda, a massive spiral galaxy a mere 2.5 million light-years away. In fact, with over twice the diameter of our own Milky Way, Andromeda is the largest nearby  galaxy. Andromeda's population of bright young stars define its sweeping spiral arms in visible light images, but here the infrared view clearly follows the lumpy dust lanes heated by the young stars as they wind even closer to the galaxy's core. Constructed to explore  Andromeda's infrared brightness and stellar populations, the full mosaic image is composed of about 3,000 individual frames. Two smaller companion galaxies, NGC 205 (below) and M32 (above) are also included in the combined fields. The data confirm that Andromeda (aka M31) houses around 1 trillion stars, compared to 4 hundred billion for the Milky Way.
这张斯皮策空间望远镜拍摄的仙女座大星系（M31）广域大图，展示了尘埃（配色红）和老年恒星（配色蓝）的细节。M31离我们约250万光年，是个巨型涡旋星系。事实上，它的直径是我们银河系的2倍多（当时数据），是我们附近最大的星系。在可见光图像中，M31中明亮的年轻恒星界定了其旋臂的范围；但在红外光图像中，清晰显示了被年轻巨星加热的尘埃带呈现为一个个团块状，这些恒星风区域逐渐旋入星系的中心。为调查仙女座大星系的红外亮度和恒星数量，组合了3000多张曝光单图构成了整个拼接图像。合成图像中还包含M31的2个小型伴星系，分别是上方的M32和下方的NGC 205。收集证据表明，M31中有大约1万亿颗恒星，而我们银河系大约仅有4000亿颗。

这是斯皮策空间望远镜拍摄的M31的详图，其实内容可以单独发个专题了，我以后有空再发吧。
IRAC超级大图下载：
尘埃和恒星合成巨图
http://ipac.jpl.nasa.gov/media_images/ssc2006-14a1.tif，14772x4953，114MB

http://ipac.jpl.nasa.gov/media_images/ssc2006-14a1.jpg，同上，大小未知

恒星大图
http://ipac.jpl.nasa.gov/media_images/ssc2006-14a2.tif，同上，83.4MB

http://ipac.jpl.nasa.gov/media_images/ssc2006-14a2.jpg，同上，大小未知

尘埃大图
http://ipac.jpl.nasa.gov/media_images/ssc2006-14a3_mac.tif，同上，59.5MB

http://ipac.jpl.nasa.gov/media_images/ssc2006-14a3.jpg，同上，大小未知

再提供一个合成大图下载
http://ipac.jpl.nasa.gov/media_images/ssc2006-14a.tif，6000x4800，29.6MB

http://ipac.jpl.nasa.gov/media_images/ssc2006-14a.jpg，同上，18.6MB

                               
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http://antwrp.gsfc.nasa.gov/apod/ap061126.html

2006.11.26的APOD再次与9#楼的一模一样。