celestial horizon

celestial-horizon的词性：
n.（名词）

1. A great circle on the celestial sphere having a plane that passes through the center of the earth and is parallel to an observer's horizon.Also called rational horizon
天球地平圈：天球上的一个大圆，有一个通过地球的中心并与观察者的视野平行的平面也作 rational horizon