How much does the direction of perihelion change each orbit ?

近日点方向使每个轨道改变了多少？

According to marsden 's calculations , this comet reaches its closest point to the sun ( perihelion ) on march 18th .

根据marsden的计算，这颗彗星会在3月18日过近日点。

Although predicting the brightness of comets with any degree of accuracy is very difficult , hale-bopp met or exceeded most predictions when it passed perihelion on april 1 , 1997 . The comet was dubbed the great comet of 1997 .

虽然预测彗星在不同角度的亮度是非常困难的，但是当1997年4月1日海尔波普彗星通过近日点时，达到甚至超过了大多数的预测。