托福聽力考試背景知識之天文學

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金星是離太陽第二近，太陽系中第六大行星。在所有行星中，金星的軌道最接近圓，偏差不到1%。中國古人稱金星為“太白”或“太白金星”，也稱“啟明”或“長庚”。古希臘人稱之為Aphrodite(阿芙羅狄蒂)，是希臘神話中愛與美的女神。而在羅馬神話中愛與美的女神是維納斯—Venus ，因此金星也稱做“維納斯”。也許是對古代人來說，它是已知行星中最亮的一顆。(也有一些異議，認為金星的命名是因為金星的表面如同女性的外貌。)金星的天文符號用維納斯的梳妝鏡來表示。金星的位相變化金星同月球一樣，也具有周期性的圓缺變化(位相變化)，但是由于金星距離地球太遠，用肉眼是無法看出來的。關于金星的位相變化，曾經被伽利略作為證明哥白尼的日心說的有力證據。

Venus is the second planet from the Sun, orbiting it every 224.7 Earth days.[11] It has nomoon. The planet is named after the Roman goddess of love and beauty. After the Earth'sMoon, it is the brightest natural object in the night sky, reaching an apparent magnitude of4.6, bright enough to cast shadows.[12] Because Venus is an inferior planet from Earth, itnever 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 whichreason 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 oftheir similar size, gravity, and bulk composition (Venus is both the closest planet to Earthand the planet closest in size to Earth). However, it has also been shown to be very differentfrom 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'ssurface 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 lockcarbon back into rocks and surface features, nor does it seem to have any organic life toabsorb it in biomass. Venus is shrouded by an opaque layer of highly reflective clouds ofsulfuric acid, preventing its surface from being seen from space in visible light. Venus may havepossessed oceans in the past,[13][14] but these would have vaporized as the temperaturerose 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 sweptinto interplanetary space by the solar wind.[16] Venus's surface is a dry desertscapeinterspersed with slab-like rocks and periodically refreshed by volcanism.

地球是距太陽第三顆，它是太陽系類地行星中最大的一顆，也是太陽系第五大行星，行星年齡估計大約有45億年(4.5×109)。地球是唯一一個不是從希臘或羅馬神中得到的名字。Earth一詞來自于古英語及日耳曼語。這里當然有許多其他語言的命名。在羅馬神話中，地球女神叫Tellus-肥沃的土地(希臘語：Gaia, 該亞， 大地母親)。直到16世紀哥白尼時代人們才明白地球只是一顆行星。

火星為距太陽第四遠，也是太陽系中第七大行星。因為火星在夜空中看起來是血紅色的，所以在西方，以羅馬神話中的戰(zhàn)神瑪爾斯Mars(或希臘神話對應的阿瑞斯—Ares)命名它�；鹦窃谑非皶r代就已經為人類所知。由于它被認為是太陽系中人類最好的住所(除地球外)，它受到科幻小說家們的喜愛。但可惜的是那條著名的被Lowell“看見”的“運河”以及其他一些什么的，都只是如Barsoomian公主們一樣是虛構的。在古代中國，因為火星熒熒如火，故稱“熒惑”。火星有兩顆小型天然衛(wèi)星：火衛(wèi)一Phobos和火衛(wèi)二 Deimos(阿瑞斯兒子們的名字)。兩顆衛(wèi)星都很小而且形狀奇特，可能是被引力捕獲的小行星。英文里前綴areo-指的就是火星。