Jovilabe

The jovilabe is a brass scientific instrument, undated and of unknown maker, currently in the collection of the Museo Galileo in Florence, Italy.

[1] The jovilabe was used by Galileo Galilei to determine the orbital periods of Jupiter's moons and to compute the times of their eclipses.

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 for the purpose.

Galileo compiled tables of the periods that he offered, with his telescopes, first to the King of Spain (1611, 1612, 1616, and 1627-1628), then to the States General of Holland (1637-1641).

To convince his Spanish interlocutors that Jupiter and its moons could be observed on unstable ground, such as a ship's deck, Galileo designed a special helmet carrying a small telescope on a hinged mount.