单项选择题 The approximate positions of the stars are based on sidereal time，which is based upon rotation of the Earth relative to（）.

单项选择题 The angle measured at the observer’s meridian from the elevated pole，clockwise or counterclockwise up to 180°，to the vertical circle of the body is the（）.

单项选择题 The angle at the pole measured through 180°from the prime meridian to the meridian of a point is known as（）.