彗星天文学时代的终结：恩克彗星的减速
The End of an Era in Cometary Astronomy: The Deceleration of Comet Encke
摘要：
值得注意的是，最近，恩克彗星的轨道运动已经受到非常轻微的非引力减速的影响。在J. F.恩克在19世纪初确定了彗星每3.3年返回近日点，他还发现该天体返回近日点的时间比牛顿理论预测的要早一些。这种加速持续了两个世纪，但其速度逐渐下降，一代又一代的彗星天文学家都很想知道彗星最终是否会在纯粹的引力轨道上运动。一个基于彗核进动假设的模型，预测加速将变成减速，直到1979年才发表。这一转变现在已经被两个独立的、高精度的轨道测定所记录。彗星持续的非引力加速的时代终于结束了。
英文摘要：
It is noted that effective very recently, the orbital motion of Encke's comet has become affected by a very slight nongravitational deceleration. Soon after J. F. Encke established in the early 19th century that the comet was returning to perihelion every 3.3 years, he also discovered that the object was notorious for returning to perihelion a little earlier than predicted by the Newtonian theory. The acceleration persisted over a period of two centuries, but its rate was gradually decreasing, Generations of cometary astronomers were curious to know whether or not the comet would eventually move in purely gravitational orbit. A model based on the assumption of a precession of the comet's nucleus, which predicted that the acceleration would change into a deceleration, was not published until 1979. This transition has now been documented by two independent, highly-accurate orbit determinations. The era of the comet's persevering nongravitational acceleration is finally over.
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