Complete or partial obscuration of an astronomical object by the moon or a planet. The precise timings of occultations provide information about planetary atmospheres, the dimensions of extended visible, radio, and X-ray objects, and the positions of objects.

Due to the rotation of the Earth, celestial objects rise in the east and set in the west. From the observer's point of view, it is called rise when the object passes the horizon ring from below to above, and it is called set vice versa. Some stars do not rise and set.

The meridian circle is a circle is a circle that passes through the zenith, nadir and celestial poles. A celestial object will reach its highest position when passing through the semi-circle which includes the zenith and the nearest celestial pole, and this phenomenon is called upper culmination. On the contrary, an object reaches its lowest position when passing through the semi-circle which includes the nadir and the nearest celestial pole, and this phenomenon is called lower culmination.

The twilight before sunrise and after sunset is due to the scattering of sunlight by the atmosphere. The time of begining and end of twilight depends on the local geographic and climate conditions. The best time for stellar observation is after the end of evening twilight and before the begining of morning twilight.

Changed of Moon phases are brough about by the non-self-luminosity and the opacity of the Moon. As the Moon is a spherical body, sunlight can only illuminate half of the Moon. Viewing from different directions, the Moon will appear to take the shapes of a circle, a semi-circle, a crescent, a gibbous or even completely invisible at all ( when its dark side faces the Earth).