sidereal

天文学家使用恒星日测量恒星位置。

Astronomers measure star positions using ___sidereal days.

恒星月比朔望月短大约两天，因为它基于恒星时间而非太阳时间。

A ___sidereal month is about two days shorter than a lunar month because it's based on star time rather than solar time.