Halley's Comet

哈雷彗星

Credit: Comet Halley as taken March 8, 1986 by W. Liller, Easter Island, part of the International Halley Watch (IHW) Large Scale Phenomena Network.

The comet named after British astronomer Edmund Halley is arguably the most famous of all comets, having been observed in 1531, 1607, 1682, 1758, 1834 ,1910 and 1986. Halley entered the picture in 1705, realizing that the appearance of 1682 was the same comet as those observed on the previous two dates listed above. Surmising that the comet was following the same laws which governed planetary orbits, he calculated the orbit corresponding to a 76 year period and predicted its return in 1758. Though he did not live to see it, the return of the comet in 1758 was a triumph for orbit calculations based on Newton's laws and led to the naming of the comet after Halley. Subsequent to Halley's analysis, historical research showed that Halley's comet had been observed at every passage since 240 BC.

以英国天文学家埃德蒙·哈雷命名的小行星可能是最著名的彗星，曾于1531年、1607年、1682年、1758年、1834年、1910年和1986年被观测到。1705年，哈雷意识到1682年的出现是上述两个日期所观测到的同一颗彗星。他推测这颗彗星遵循着支配行星轨道的相同规律，计算出其轨道周期为76年，并预测了1758年的回归。尽管他未能亲眼看到这次回归，但1758年彗星的回归是对基于牛顿定律轨道计算的胜利，也促成了这颗彗星以哈雷的名字命名。在哈雷分析之后，历史研究显示，自公元前240年以来，这颗彗星在每次出现时都有被观测到。

Nucleus of Halley's Comet

哈雷彗星的核

With such a long history of observations, we were well prepared for Halley's 1986 visit. The Soviet spacecraft Vega 2 traveled through the comet's coma, passing within 8000 km of the nucleus. With data obtained from that encounter, spacecraft Giotto was navigated to within 600 km of the nucleus and obtained our first direct images of a comet nucleus. Giotto's images showed the nucleus to be an irregular object, something like a potato, with dimensions 15 km long and up to 10 km wide. If the common "dirty snowball" view applies at all, this was a very dirty one, appearing almost jet black. The visible jets coming from the dark nucleus were not uniform, but emanated from several small vents on the sunlit side. These vents could actually produce measurable changes in the comet's orbit, and were our first clue about the origin of observed small departures of comet orbits from Kepler's laws.

凭借如此悠久的观测历史，我们已为哈雷彗星1986年的来访做好了准备。苏联航天器维加2号穿越了彗星的彗发，飞过距离彗核仅8000公里的地方。借助这次相遇获得的数据，航天器吉奥蒂奥被导航至距离彗核仅600公里处，并获得了彗核的首张直接影像。吉奥蒂奥的影像显示，彗核是一个不规则的天体，形状类似土豆，尺寸为15公里长，宽达10公里。如果“脏雪球”观点在某种程度上适用，那么这颗彗核则非常脏，看起来几乎呈黑色。从黑色彗核发出的可见喷流并不均匀，而是从阳光照射的一面几个小孔喷出。这些孔洞实际上可以产生可测量的彗星轨道变化，并成为我们理解观测到的彗星轨道偏离开普勒定律的起源的第一个线索。

照片摄于1986年3月8日，由W. Liller在厄瓜多尔岛拍摄，属于国际哈雷观测（IHW）大规模现象网络。