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Giambattista Riccioli, Almagestum novum (Bologna, 1651), Part 2

The New Almagest

The frontispiece of Riccioli’s treatise depicts not two, but three major systems of the world.

1. The Ptolemaic system rests discarded (lower right corner) because of the phases of Venus and Mercury (upper left corner). All-seeing Argus looks on, holding a telescope. Urania weighs in a balance the two chief world systems which remain: 

2. The Copernican system appears as the standard against which alternatives must be measured. 

3. Riccioli’s semi-Tychonic system weighs in as the most warranted. 

A comet and several telescopic discoveries (upper right corner) include the banded appearance of Jupiter and the ring of Saturn.

See Scott L. Montgomery, The Moon and the Western Imagination (Arizona, 1999).

By 1651, the reform of Jesuit astronomy initiated by Clavius a half-century earlier, which spread to China via Ricci, Schreck and Schall, and which was sidetracked by the Galileo affair, was taken up again in Italy by Riccioli. The Jesuits needed a comprehensive new astronomy, a new Almagest. That is just what Riccioli provided in the Almagestum novum. Riccioli’s new astronomy embraced the reality of sunspots and the corruption of the heavens, and encouraged experimentation with various Tychonic and semi-Tychonic systems.

Riccioli’s frontispiece indicates that Copernicanism was admired as the standard by which the mathematical aspects of other systems were judged, but alternatives proliferated rapidly as the search for observable distinguishing evidence bogged down. Transformations of systems threw all in doubt. In terms of predicting planetary positions, competing systems were not just empirically similar, but geometrically equivalent. 

The absence of stellar parallax and the resulting implication of the remarkable immensity of stars was a recurring problem for the Copernican system. Riccioli also reports telescopic star sizes from 18 secs for Sirius to 4 secs for Algol, smaller than the maximum limit of 60 secs according to Tycho’s non-telescopic estimate, but still large enough for tiny Algol to make up half the Earth’s orbit if the Copernican system were correct. 

See Christopher M. Graney, Setting Aside all Authority:  Giovanni Battista Riccioli and the Science against Copernicus in the Age of Galileo (Notre Dame, 2015), Ch. 9.


Latin text in the frontispiece from the Vulgate:

“Numerus, Mensura, Pondus”: “tuae sed omnia mensura et numero et pondere disposuisti”; “but thou hast ordered all things in measure, and number, and weight” (The Wisdom of Solomon 11:21 DOUAY)).

Psalm 18:3: “dies diei eructat verbum et nox nocti indicat scientiam”; “Day to day uttereth speech, and night to night sheweth knowledge” (Psalms 18:3 DOUAY).

Psalm 8:4: “videbo caelos tuos; opera digitorum tuorum”; “For I will behold thy heavens, the works of thy fingers: the moon and the stars which thou hast founded” (Psalms 8:4 DOUAY).

Psalm 103:5: “non inclinabitur in saeculum saeculi”; “Who hast founded the Earth upon its own bases: it shall not be moved for ever and ever” (Psalms 103:5 DOUAY).

This is Part 2 of the New Almagest.  Part 1, bound separately, is displayed in the Moon and the Telescope gallery.

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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.