Ancient astronomers, such as Hipparchus (in the second century B.C.E.) and Ptolemy (in the second century C.E.), used instruments such as a sundial, a triquetrum (a sort of triangular ruler), and a plinth (a stone block with an engraved arc) to chart the positions and motions of planets and celestial objects.

By the sixteenth century C.E., complex observational tools had been invented. The famous Danish astronomer Tycho Brahe (1546–1601), for example, crafted many of his own instruments, including a sextant, a quadrant with a radius of six feet (almost two meters), a two-piece arc, an astrolabe, and various armillary spheres.