Replica of Galilaean Giovilabio

This is a replica of a calculating instrument designed by Galileo Galilei to make use of his observations of the movements of four moons of the planet Jupiter. Galileo (1564–1642) sought to demonstrate that the moon’s regular motions could be used to determine time and that this, along with the positions of stars, could be used to determine longitude. He applied to the Spanish crown for its longitude prize, but was unsuccessful because the device was not considered practical.
On this instrument, the larger of the two revolving discs represents Jupiter and the smaller one the Sun. The discs are connected and their movements show when the four moons, observed from the Earth, enter and leave the shadow of Jupiter. The instrument’s plate is engraved in Latin with tables to predict these eclipses and it can also indicate time (though less precisely) from the observed positions of the moons.
Galileo discovered the moons of Jupiter in 1610 with a telescope of his own invention, and he used it to study their motions. In designing the giovilabio, he found it necessary to correct his earlier observations for the effect of the Earth’s revolution around the Sun, which added to the growing evidence supporting the Copernican system of a Sun-centered universe. It also seemed to contradict the traditional (Aristotelian) cosmology, supported by the Catholic Church, which theorized a stationary Earth about which all heavenly bodies moved. Galileo’s support for the Copernican system ultimately led to his trial and conviction for heresy.
1. Bedini, Silvio A. “The Galilean Jovilabe,“ Nuncius, 1, 1986, pp. 25-46.
2. Bedini , Silvio A. The Pulse of Time: Galileo, the Determination of Longitude, and the Pendulum Clock, Florence: Leo S. Olschki, 1991, pp. 7-21.
3. G. Vanpaemel, "Science Disdained: Galileo and the Problem of Longitude," Italian Scientists in the Low Countries in the XVIIth and XVIIIth Centuries, Edited by C. S. Maffeoli and L. C. Palm, Amsterdam: Rodopi, 1989, pp. 111-129.
4. The Jovilabe: History and Design., accessed March 31, 2013.
Physical Description
brass (overall material)
overall: 8 cm x 20 cm x 41 cm; 3 5/32 in x 7 7/8 in x 16 5/32 in
ID Number
catalog number
accession number
See more items in
Medicine and Science: Physical Sciences
Measuring & Mapping
Time and Navigation
Time and Navigation, National Air and Space Museum
Data Source
National Museum of American History


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