sidereal — relating to or determined by the stars or constellations

an elderly astronomer adjusts a large brass astrolabe while pointing up at specific constellations overhead. He carefully aligns the instrument's circular rings with the bright stars of Orion and the Big Dipper. The astrolabe's markings correspond exactly to the star patterns visible in the dark sky above. As he rotates the device, it matches the precise positions of the celestial bodies. A young apprentice holds a scroll showing star charts and watches intently as the master demonstrates. Several other astronomical instruments like armillary spheres and quadrants are positioned around them, all designed to track stellar movements. calculations and observations being determined by the stars and constellations