Quadrans Muralis is an ancient astronomical instrument used to measure angles in the sky. It resembles a large quarter circle and was typically mounted on a wall. This tool helped astronomers and navigators determine the position of celestial bodies, which was essential for navigation and timekeeping in the past. The Quadrans Muralis was invented by the famous astronomer Tycho Brahe in the late 16th century. It allowed for more accurate observations than previous instruments. By using this device, Brahe made significant contributions to the field of astronomy, paving the way for future scientists like Johannes Kepler to develop their theories about planetary motion.