Geminiano Montanari (June 1, 1633 - October 13, 1687) was an Italian astronomer, lens-maker, and proponent of the experimental approach to science. In 1662 or 1663 he drew an accurate map of the Moon using an ocular micrometer of his own making. He also made observations on capillarity and other problems in statics, and suggested that the viscosity of a liquid depended on the shape of its molecules. He is best known for his observation, made around 1667, that the second brightest star in the constellation of Perseus varied in brightness. It is likely that others had observed this effect before, but he was the first named astronomer to record it. In 1669 he succeeded Giovanni Cassini as astronomy teacher at the observatory of Panzano. In 1676 he reported a sighting of a comet to Edmund Halley. In 1679 Montanari moved to a teaching post in Padua, but almost all records of this period of his life have been lost. A letter survives from 1682 recording a sighting of Halley's Comet. He died in 1687 at the age of 54.