- a clock indicating or representing the movements of the sun or planets, the phases of the moon, or the sky visible at a given time, used as a means of establishing time or for additional information, as locating celestial bodies or timing their movement.
- a clock used for observing the apparent time of the meridian passages of heavenly bodies.
- a complex clock showing astronomical phenomena, such as the phases of the moon
- any clock showing sidereal time used in observatories
