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Oratio Grassi, Ratio ponderum librae et simbellae (Naples, 1627)

A Comparison of the Weights for the Astronomical Balance and the Small Scale (of the Assayer)

The Jesuit astronomers who had celebrated Galileo’s telescopic discoveries during his visit to Rome in 1611 now felt estranged by the biting satire of the The Assayer. The controversy concluded with this final reply. 

Both comets and cosmic systems remained enigmas. If mathematical methods and the evidence available at the time could not disprove the Tychonic system, then Galileo faced the daunting prospect that scientific knowledge might be provisional, with certainty an elusive goal, even in mathematics.

Galileo's World Exhibition Location

Source: History of Science Collections

Section: Controversy

Section Number: 3

Object Number: 36

Subject Area(s): Astronomy, Philosophy

Time Period: 17th Century

Region(s): Europe, Italy

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Exhibit Gallery OERs

Phases of Venus: Riccioli, New Almagest

Phases of Venus-Riccioli

The phases of Venus were an item of discussion in early modern Europe as scientists sought to determine whether it was evidence of the heliocentric system. Yet among the scientists it was anything but conclusive that this evidence proved the sun-centered universe. Learn more in this learning leaflet.


Six Cosmological Systems: Phases of Venus

Kircher-Cosmological Systems-Venus

It is often thought that Galileo's discovery of the phases of venus demonstrated the contested heliocentric model of the universe. However, such an understanding is overly simplistic of the early modern account of astronomy. Use this learning leaflet to learn more.


Elisabeth Hevelius: Observational Astronomer

Elisabeth Hevelius Learning Leaflet

How does the Sextant symbolize the person who worked on the famed Hevelius star catalog and star atlas throughout its production, from observation to publication? 

Elisabeth Hevelius, wife of Johann Hevelius, was an astronomer in her own right. They worked together in the observatory of their Gdansk home to measure angular widths and distances with a great sextant, which required two observers at a time. The Sextant was among the new constellations they proposed in Uranographia (1690), the most detailed and influential celestial atlas of the 17th century. The Uranographia contains 54 beautiful double page engraved plates of 73 constellations, and 2 oversized folding plates of planispheres.