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哈雷彗星的故事
哈雷彗星每隔76年便重返地球的夜空，這顆彗星的命名，其實是紀念17世紀英國天文學家愛德蒙．哈雷，他是首個準確計算哈雷彗星回歸，並因此證明彗星周期特性的人。年輕的哈雷已憑其南天觀測而成為聲名顯赫的天文學家，但一直困擾他的是欠缺科學理據的開普勒行星定律。1684年，他終於決定前往劍橋探訪牛頓，得悉原來牛頓早把問題解決，只是未有公開發表。哈雷在興奮之餘，決定自資把牛頓的著作付梓，這便是劃時代巨著《自然哲學的數學原理》。哈雷於1705年採用牛頓引力定律，計算出他觀測過的1682年彗星，原來是在1531年及1607年出現過的大彗星，他遂大膽預言這顆彗星會於1785年再次回歸。哈雷於1742年離世，他的彗星果真應約，在1785年的聖誕節給天文界帶來驚喜。
The Story of Comet Halley
The great comet that returns to our sky every 76 years was named after Edmond Halley. Halley was the first person to correctly predict the return of a comet and thus revealing its periodical nature. The young astronomer was much fascinated with Kepler's laws of planetary motion because there were not any scientific explainations. In 1684 he decided to pay a visit to Newton only to learn that Newton had solved the problem. Halley was so excited that he decided to publish Newton's work at his own expense. In 1687 The Principia marked its place in the history of science. In 1705, applying Newton's gravitational laws, Halley carefully calculated the orbit of the 1682 great comet. He concluded that this comet was the same one that appeared in 1531 and 1607. He went on to predict that the comet would return in 1785. Halley did not live to witness his 1785 Christmas star. He died in 1742. ■甄枝強 資深天文愛好者 圖片鳴謝：NASA/W. Liller
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