天文学背景知识科普来啦（上）

嗅觉Y不缺失

天文学是研究宇宙空间天体、宇宙的结构和发展的学科。内容包括天体的构造、性质和运行规律等。天文学是一门古老的科学，自有人类文明史以来，天文学就有重要的地位。天文学作为托福常考学科，除了天文学专业的学生，大多数学生却没有很多的机会了解相关的背景知识，那今天我们就来看看这神奇又美丽的宇宙（cosmos）吧!

来，看看我们的太阳系!
太阳系是一个以太阳为中心，受太阳引力约束在一起的天体系统，包括太阳、行星及其卫星、矮行星、小行星、彗星和行星际物质。 太阳系位于距银河系中心大约2.4~2.7万光年的位置（银河系的恒星数量约在1000亿到4000亿之间，太阳只是其中之一）



太阳系Solar system   
太阳sun      
行星planet   
卫星satellite      
矮行星dwarf
小行星asteroid      
彗星comet  
恒星 star   
银河系galaxy   
光年light year



太阳系里面有八大行星 (Eight Planets)，他们的命名多来自于古罗马神话（mythology）：

1. mercury 水星（因快速运动而得名）
水星是太阳系的八大行星中最小且最靠近太阳的行星。轨道周期是87.9691天，是太阳系中轨道周期最短的行星。它以罗马商业之神墨丘比斯命名，墨丘比斯是众神的信使，是众神和凡人之间的连接，对应着希腊的赫尔墨斯神。
Mercury  is the smallest planet in the Solar System and the closest to the Sun.  Its orbit around the Sun takes 87.97 Earth days, the shortest of all the  Sun's planets. It is named after the Roman god Mercurius (Mercury), god  of commerce, messenger of the gods, and mediator between gods and  mortals, corresponding to the Greek god Hermes




2. Venus  金星（因为表面亮丽而得名）
金星是离太阳第二远的行星。它是以罗马爱与美女神的名字命名的。除去月球，金星是地球夜空中最亮的自然天体，它能投射阴影，在极少见的情况下，肉眼也能看到。金星位于地球的轨道内，也似乎从不远离太阳，要么在黄昏后从西边落下，要么在黎明前从东边升起。

Venus  is the second planet from the Sun. It is named after the Roman goddess  of love and beauty. As the brightest natural object in Earth's night sky  after the Moon, Venus can cast shadows and can be, on rare occasions,  visible to the naked eye in broad daylight.Venus lies within Earth's  orbit, and so never appears to venture far from the Sun, either setting  in the west just after dusk or rising in the east a little while before  dawn.



3. Earth  地球（Earth来自于日耳曼语。地球女神叫Tellus肥沃土地）
地球是太阳系由内及外的第三颗行星，也是已知的唯一能够孕育生命的天体。地球表面约有29.2%陆地，包括大陆和岛屿。其余70.8%是水，大部分是海洋、海洋、海湾和其他咸水水体，也有湖泊、河流和其他淡水，它们共同构成地球的水圈。地球的极地地区大部分覆盖着冰川。

Earth  is the third planet from the Sun and the only astronomical object known  to harbor and support life. About 29.2% of Earth's surface is land  consisting of continents and islands. The remaining 70.8% is covered  with water, mostly by oceans, seas, gulfs, and other salt-water bodies,  but also by lakes, rivers, and other freshwater, which together  constitute the hydrosphere. Much of Earth's polar regions are covered in  ice.



4. Mars 火星（由于它鲜红的颜色而得名；有时被称为“红色行星”，趣记：在希腊人之前，古罗马人曾把火星作为农耕之神来供奉。而好侵略扩张的希腊人却把火星作为战争的象征，而三月份的名字也是得自于火星）
火星是太阳由内及外的第四颗行星，也是太阳系中第二小的行星。在英语中，Mars是罗马战神的名字，因此火星经常被称为“红色星球”。后者指的是火星表面普遍存在的氧化铁所带来的变化，它使火星呈现红色，这在肉眼可见的天体中是独一无二的。火星是一颗大气层稀薄的类地行星，其表面特征让人想起月球上的陨石坑和地球上的山谷、沙漠和极地冰盖。

Mars  is the fourth planet from the Sun and the second-smallest planet in the  Solar System. In English, Mars carries the name of the Roman god of war  and is often referred to as the "Red Planet".The latter refers to the  effect of the iron oxide prevalent on Mars's surface, which gives it a  reddish appearance, that is distinctive among the astronomical bodies  visible to the naked eye. Mars is a terrestrial planet with a thin  atmosphere, with surface features reminiscent of the impact craters of  the Moon and the valleys, deserts and polar ice caps of Earth.



5. Jupiter 木星 （是上帝之王，因为体积大而得名）
木星是太阳由内及外的第五颗行星，也是太阳系中最大的行星。木星是一团巨大的气体，体积是太阳系其他行星体积总和的两点五倍，但比太阳体积的千分之一小一些。从地球的夜空观测，它的亮度仅次于月球和金星。人们从史前开始观测木星。它因为体积巨大而得到了罗马众神之首宙斯之名。

Jupiter  is the fifth planet from the Sun and the largest in the Solar System.  It is a gas giant with a mass more than two and a half times that of all  the other planets in the Solar System combined, but slightly less than  one-thousandth the mass of the Sun. Jupiter is the third-brightest  natural object in the Earth's night sky after the Moon and Venus. It has  been observed since pre-historic times and is named after the Roman god  Jupiter, the king of the gods, because of its observed size.



6.Saturn 土星（希腊神话中的农神Cronus是Uranus天王星和盖亚的儿子，也是宙斯木星的父亲。土星也是英语中“星期六”Saturday的词根。）
木星是太阳由内及外的第六颗行星，也是太阳系中第二大的行星，次于木星。木星是一团巨大的气体，平均半径大约为地球的九点五倍。虽然密度仅为地球的八分之一，但是质量是地球的九十五倍还多。木星得名于罗马的财富和农业之神。

Saturn  is the sixth planet from the Sun and the second-largest in the Solar  System, after Jupiter. It is a gas giant with an average radius of about  nine and a half times that of Earth. It only has one-eighth the average  density of Earth; however, with its larger volume, Saturn is over 95  times more massive.Saturn is named after the Roman god of wealth and  agriculture.



7. Uranus  天王星（Uranus是古希腊神话中的宇宙之神，是最早的至高无上的神。他是盖亚的儿子兼配偶，是Cronus农神土星、独眼巨人和泰坦的父亲）
天王星是太阳由内及外第七颗行星。它的名字来源于希腊的天空之神Uranus。基于希腊神话，Uranus是阿瑞斯（Mars）的曾祖父，宙斯(Jupiter)的祖父和克罗诺斯(Saturn)的父亲。在太阳系中，它的半径排名第三，质量排名第四。天王星和海王星的组成成分相似，拥有大块的化学物质和气体行星木星和土星不同。因此，科学家们经常把天王星和海王星归为“冰巨星”来区别于其他巨行星。天王星的大气主要成分和木星和土星相似是氢和氦，但它含有更多的“冰”，例如水、氨、甲烷，以及其他碳氢化合物的痕迹。它是太阳系中最冷的行星大气，最低温度为49 K(224°C;371°F)，并有一个复杂的分层云结构，其中水被认为是构成最低层的云，甲烷是最上层的云。天王星的内部主要为冰和岩石。

Uranus  is the seventh planet from the Sun. Its name is a reference to the  Greek god of the sky, Uranus, who, according to Greek mythology, was the  great-grandfather of Ares (Mars), grandfather of Zeus (Jupiter) and  father of Cronus (Saturn). It has the third-largest planetary radius and  fourth-largest planetary mass in the Solar System. Uranus is similar in  composition to Neptune, and both have bulk chemical compositions which  differ from that of the larger gas giants Jupiter and Saturn. For this  reason, scientists often classify Uranus and Neptune as "ice giants" to  distinguish them from the other giant planets. Uranus's atmosphere is  similar to Jupiter's and Saturn's in its primary composition of hydrogen  and helium, but it contains more "ices" such as water, ammonia, and  methane, along with traces of other hydrocarbons.It has the coldest  planetary atmosphere in the Solar System, with a minimum temperature of  49 K (224 °C; 371 °F), and has a complex, layered cloud structure with  water thought to make up the lowest clouds and methane the uppermost  layer of clouds.The interior of Uranus is mainly composed of ices and  rock.



8. Neptune 海王星（是古罗马神话中的海神Poseidon。）
海王星是太阳系从内向外第八课行星，也是离太阳最远的行星。在太阳系中，它是直径第四，质量第三，密度最大的巨行星。它的质量是地球的十七倍，比它的双胞胎天王星大那么一点。 海王星因为质量巨大导致了更多来自大气的引力压缩，所以它比天王星的密度大且体积小。

Neptune  is the eighth and farthest-known Solar planet from the Sun. In the  Solar System, it is the fourth-largest planet by diameter, the  third-most-massive planet, and the densest giant planet. It is 17 times  the mass of Earth, slightly more massive than its near-twin Uranus.  Neptune is denser and physically smaller than Uranus because its greater  mass causes more gravitational compression of its atmosphere.



9. Pluto  冥王星（是因为它太小了甚至是比我们月球还要小。所有科学家将他成为矮行星）
迄今为止，冥王星是凯伯带轨道中最早发现的最大的矮行星。1930年，人们发现了冥王星，宣布它为太阳系第九颗行星。从1990年开始，人们发现了凯伯带中一系列的小天体，包括矮行星艾瑞斯，这这一发现使得冥王星作为行星的地位受到了质疑。2006年，国际天文联合会正式将冥王星从行星中除名并划分为矮行星。

Pluto  is a dwarf planet in the Kuiper belt, a ring of bodies beyond the orbit  of Neptune. It was the first and the largest Kuiper belt object to be  discovered. After Pluto was discovered in 1930, it was declared to be  the ninth planet from the Sun. Beginning in the 1990s, its status as a  planet was questioned following the discovery of several objects of  similar size in the Kuiper belt and the scattered disc, including the  dwarf planet Eris. This led the International Astronomical Union (IAU)  in 2006 to formally define the term "planet"—excluding Pluto and  reclassifying it as a dwarf planet.