The astronomical calendar, also known as the celestial calendar, is a system of measuring time based on the movements of celestial bodies. It is used to track the annual positions of the sun, moon and stars, and is often used in astrology and astronomy. Synonyms for the astronomical calendar include the celestial timetable, the cosmic chronology, the celestial timetable and the astrological agenda. Other related terms include the lunar calendar, the solar calendar and the sidereal calendar, which track the movements of the moon, sun and stars respectively. These calendars have been used by many ancient civilizations throughout history and continue to be of significance to modern astrologers, astronomers and astronomers alike.