历史今天:1846年海王星被发现(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.

【中文译文】

海王星是太阳系第八大行星，也是太阳系最远的行星。以罗马的海神命名的这个星球，是太阳系中直径第4大，质量第三大的行星。海王星质量是地球的17倍，略超过其近邻天王星，而天王星质量是地球的15倍。海王星轨道距太阳的平均距离是30.1天文单位，约是地球到太阳距离的30倍。它的天文符号是，是希腊神话的海神波塞冬使用的三叉戟。

于1846年9月23日发现的海王星是第一个行星的数学预测发现，而不是由经验观察发现的。在天王星的轨道变化导致天文学家们推断，它的轨道还受另一个未知受行星的引力影响。海王星后来在其预测的位置度被发现了，其最大的卫星海卫，不久也被发现，而其余12个卫星直到20世纪才被确切的定位。至目前为止，只有旅行者2号在1989年8月25日造访过海王星。

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