金星是离太阳第二近，太阳系中第六大行星。在所有行星中，金星的轨道最接近圆，偏差不到1%。中国古人称金星为“太白”或“太白金星”，也称“启明”或“长庚”。古希腊人称之为Aphrodite(阿芙罗狄蒂)，是希腊神话中爱与美的女神。而在罗马神话中爱与美的女神是维纳斯—Venus ，因此金星也称做“维纳斯”。也许是对古代人来说，它是已知行星中最亮的一颗。(也有一些异议，认为金星的命名是因为金星的表面如同女性的外貌。)金星的天文符号用维纳斯的梳妆镜来表示。金星的位相变化金星同月球一样，也具有周期性的圆缺变化(位相变化)，但是由于金星距离地球太远，用肉眼是无法看出来的。关于金星的位相变化，曾经被伽利略作为证明哥白尼的日心说的有力证据。
Venus is the second planet from the Sun, orbiting it every 224.7 Earth days.[11] It has no moon. The planet is named after the Roman goddess of love and beauty. After the Earth's Moon, it is the brightest natural object in the night sky, reaching an apparent magnitude of 4.6, bright enough to cast shadows.[12] Because Venus is an inferior planet from Earth, it never appears to venture far from the Sun: its elongation reaches a maximum of 47.8°. Venus reaches its maximum brightness shortly before sunrise or shortly after sunset, for which reason it has been referred to by ancient cultures as the Morning Star or Evening Star.
Venus is a terrestrial planet and is sometimes called Earth's "sister planet" because of their similar size, gravity, and bulk composition (Venus is both the closest planet to Earth and the planet closest in size to Earth). However, it has also been shown to be very different from Earth in other respects. It has the densest atmosphere of the four terrestrial planets, consisting of more than 96% carbon dioxide. The atmospheric pressure at the planet's surface is 92 times that of Earth's. With a mean surface temperature of 735 K (462 °C; 863 °F), Venus is by far the hottest planet in the Solar System. It has no carbon cycle to lock carbon back into rocks and surface features, nor does it seem to have any organic life to absorb it in biomass. Venus is shrouded by an opaque layer of highly reflective clouds of sulfuric acid, preventing its surface from being seen from space in visible light. Venus may have possessed oceans in the past,[13][14] but these would have vaporized as the temperature rose due to a runaway greenhouse effect.[15] The water has most probably photodissociated, and, because of the lack of a planetary magnetic field, the free hydrogen has been swept into interplanetary space by the solar wind.[16] Venus's surface is a dry desertscape interspersed with slab-like rocks and periodically refreshed by volcanism.
地球是距太阳第三颗，它是太阳系类地行星中最大的一颗，也是太阳系第五大行星，行星年龄估计大约有45亿年(4.5×109)。地球是唯一一个不是从希腊或罗马神中得到的名字。Earth一词来自于古英语及日耳曼语。这里当然有许多其他语言的命名。在罗马神话中，地球女神叫Tellus-肥沃的土地(希腊语：Gaia，该亚，大地母亲)。直到16世纪哥白尼时代人们才明白地球只是一颗行星。
火星为距太阳第四远，也是太阳系中第七大行星。因为火星在夜空中看起来是血红色的，所以在西方，以罗马神话中的战神玛尔斯Mars(或希腊神话对应的阿瑞斯—Ares)命名它。火星在史前时代就已经为人类所知。由于它被认为是太阳系中人类最好的住所(除地球外)，它受到科幻小说家们的喜爱。但可惜的是那条着名的被Lowell“看见”的“运河”以及其他一些什么的，都只是如Barsoomian公主们一样是虚构的。在古代中国，因为火星荧荧如火，故称“荧惑”。火星有两颗小型天然卫星：火卫一Phobos和火卫二 Deimos(阿瑞斯儿子们的名字)。两颗卫星都很小而且形状奇特，可能是被引力捕获的小行星。英文里前缀areo-指的就是火星。
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