Hevelius and His Wife Portable sextants were used to chart a ship’s position at sea by measuring the altitude of celestial bodies above the horizon. Astronomers used much larger sextants to measure the angular distances between two bodies. Here, Johannes Hevelius makes use of the great brass sextant at the Danzig observatory, with the help of his wife, Elisabetha. Six feet in radius, this instrument was closely modeled on the one used by Tycho Brahe.
(Engraving from Machina Coelestis, 1673, by Johannes Hevelius/SSPL/Getty Images)