It 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 the Sun, Moon, and stars. It was important to astrologers and mariners. It also served to determine local time and was used in navigation.
The astrolabe's appearance: It is a large brass or copper circle, whlch is comprised of two circular discs held together in the centre by a pin.
The Body of the Astrolabe: The upper blue part of the sphere represents the sky above the horizon. The sun pointer is there during the day. The lower part of the 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. On the perimeter of the astrolabe is the twenty-four-hour dial - a moving ring with Arabic numerals where the golden hand tells Old Bohemian Time. Roman numerals are denoted below it. 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.