An astronomical clock is a clock that displays astronomical information in addition to the time, such as the phases of the moon, the position of the sun and moon in the zodiac, the times of sunrise and sunset, the tides, or sidereal time. Some also show the equation of time, the difference between solar time and mean time.
The earliest examples were great public clocks in medieval cathedrals and town halls, such as those at Wells, Strasbourg and Prague, which presented the heavens in elaborate painted dials. Domestic astronomical clocks became more common from the seventeenth century, when English, French and German makers produced bracket and longcase clocks with subsidiary dials and complex calendar work. Many eighteenth-century longcase clocks include a simple moon-phase or high-tide dial, while fully astronomical regulators and orreries were made by the leading makers for scientific patrons. Collectors value originality of the movement and dials, the quality of the engraving and finishing, a known maker and a complete, working mechanism. Because astronomical work is intricate, restoration should be carried out by a specialist familiar with complicated movements.
