Jovilabe
The jovilabe is a brass scientific instrument, undated and of unknown maker, currently in the collection of the Museo Galileo in Florence, Italy. The jovilabe was used by Galileo Galilei to determine the orbital periods of Moons of Jupiter, Jupiter's moons and to compute the times of their eclipses. The instrument is engraved with tables showing the mean motions of each of the four moons. Two connected disks of different diameters are rotated by means of a movable rod. They are used to create a "view from the Sun" of the movements of Jupiter's moons observed from the Earth (movements that seem irregular because of the heliocentric motions of the Earth and Jupiter). After announcing the discovery of Jupiter's moons in his 1610 treatise ''Sidereus Nuncius'', Galileo began the systematic study of their periods in 1611, developing a Micrometer (device), micrometer for the purpose. Galileo immediately realized that eclipses of the moons could provide a precise method to determine longit ...
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