Prague Astronomical Clock - structure and time reading
The AstrolabeIt is the cornerstone of every medieval astronomical clock. It is an astronomical instrument whose origin dates to Classical Antiquity. It was used to determine the positions of Sun, Moon and stars. It was important to astrologers and mariners. It also served to determine local time and was used in navigation.
Astrolabe itself is a large brass or copper circle comprised of two circular discs held together in the centre by a pin. The Sky section, or the upper blue part of the astrolabe sphere, represents day time. The sun pointer travels around it during the day. The lower part of the astrolabe sphere represents night, with part of dawn (Aurora) and sunrise (Ortus) painted red on the left, and sunset (Occasus) and nightfall depicted on the right. The Earth is depicted in the center of the astrolabe. Additionally, there are two concentric circles there: the Tropic of Capricorn and the Tropic of Cancer. There is an unmarked equator between them.
The astrolabe holds three time scales: Old Bohemian Time is shown using Gothical numerals on the moving Outer Ring, Central European Time is shown using Latin numerals at the outer edge of the astrolabe and Babylonian Time is shown using Arabic numerals on the Sky section of the astrolabe.