The correct answer to this open question is the following.
Alexis Clairaut's prediction correct prediction of when Halley's comet would return was important because it proved that Isaac Newton's theories of motion and gravity were correct.
Alexis Clairaut (1713-1765) was a French astronomer and mathematician that validated some of the principles that were established by Isaac Newton. He obtained the result for the apsidal precession of the orbit of the moon. He was a smart scientist that wrote documents about the size of planet Venus, the orbit of the moon, the motion of the comets and how affected planet Eart, and he put special attention to Haley's Comet.