歷史今天:1846年海王星被發現(9.23)

【英文原文】

Neptune is the eighth and outermost-known planet from the Sun in the Solar System. Named for the Roman god of the sea, it is the fourth-largest planet by diameter and the third-largest by mass. Neptune is 17 times the mass of Earth and is slightly more massive than its near-twin Uranus, which is 15 Earth masses and not as dense. On average, Neptune orbits the Sun at a distance of 30.1 AU, approximately 30 times the Earth-Sun distance. Its astronomical symbol is , a stylized version of the god Neptune's trident.

Discovered on September 23, 1846, Neptune was the first planet found by mathematical prediction rather than by empirical observation. Unexpected changes in the orbit of Uranus led astronomers to deduce that its orbit was subject to gravitational perturbation by an unknown planet. Neptune was subsequently found within a degree of its predicted position, and its largest moon, Triton, was discovered shortly thereafter, though none of the planet's remaining 12 moons was located telescopically until the 20th century. Neptune has been visited by only one spacecraft, Voyager 2, which flew by the planet on August 25, 1989.

【中文譯文】

海王星是太陽系第八大行星，也是太陽系最遠的行星。以羅馬的海神命名的這個星球，是太陽系中直徑第4大，質量第三大的行星。海王星質量是地球的17倍，略超過其近鄰天王星，而天王星質量是地球的15倍。海王星軌道距太陽的平均距離是30.1天文單位，約是地球到太陽距離的30倍。它的天文符號是，是希臘神話的海神波塞冬使用的三叉戟。

於1846年9月23日發現的海王星是第一個行星的數學預測發現，而不是由經驗觀察發現的。在天王星的軌道變化導致天文學家們推斷，它的軌道還受另一個未知受行星的引力影響。海王星後來在其預測的位置度被發現了，其最大的衛星海衛，不久也被發現，而其餘12個衛星直到20世紀才被確切的定位。至目前爲止，只有旅行者2號在1989年8月25日造訪過海王星。

The internal structure of Neptune:
1. Upper atmosphere, top clouds
2. Atmosphere consisting of hydrogen, helium and methane gas
3. Mantle consisting of water, ammonia and methane ices
4. Core consisting of rock and ice