How the Astronomical Clock keeps three kinds of time

The Astronomical Clock has hung on the Old Town Hall since 1410. Most people watch the apostles parade on the hour, then walk away; the dial is worth a longer look.

The golden hand shows the hour three ways. On the outer ring of Schwabacher numerals it counts the hours from sunset, Old Czech time; the Roman numerals give the time we use today; and a small star moves around the zodiac ring for sidereal, or star, time.

The sun and moon travel around the dial too, the moon turning to show its phase. Below, the calendar plate after the painter Josef Mánes marks every day of the year with a saint’s name.