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Primary sourceBook1632

Dialogue Concerning the Two Chief World Systems

Galileo Galilei · 1632

Galileo's 1632 Italian-language book comparing the Copernican and Ptolemaic systems, which led to his trial.

Galileo's own defence of Copernicanism, the book whose publication triggered his trial by the Inquisition.

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Title page of the 1632 Florentine edition of Galileo Galilei's Dialogo, printed in large serif capitals with a decorative woodcut emblem, imprint 'In Fiorenza, Per Gio: Batista Landini MDCXXXII', and several library stamps and handwritten shelf marks.
Galileo Galilei, Dialogo sopra i due massimi sistemi del mondo, title page, Florence, 1632.

About this source

What it is

This book, written in Italian by Galileo Galilei and published in Florence in 1632, is structured as four days of dialogue between three characters debating whether the Earth or the Sun is the centre of the universe.

Why it matters

Although formally presenting both sides, the book clearly favours the Copernican, Sun-centred view. Its publication, under licence from the Inquisition, led in 1633 to Galileo being found 'vehemently suspect of heresy', and the book was banned for two centuries. It shows how dangerous new scientific ideas could be when they clashed with religious authority.

Look closer

  • Why might Galileo have chosen to write in Italian rather than Latin, and as a dialogue rather than a straightforward argument?
  • What might the character names Salviati, Sagredo and Simplicio tell you about Galileo's intentions?
  • Why do you think the book still needed official Church approval before it could be printed?

This book is part of the curated material that grounds the AI version of Galileo Galilei and Nicolaus Copernicus on Humy.ai — when students ask about related events, the AI can quote it and cite it.

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Title page of the 1610 Latin book Sidereus Nuncius by Galileo Galilei, printed in Venice by Thomas Baglionus. Black text in several type styles, with a central woodcut emblem of a seated figure in an oval frame flanked by cherubs. Handwritten shelfmark appears at the bottom.Book

Primary source

Sidereus Nuncius

Galileo Galilei · 1610

Engraved oval portrait print of a bearded older man with receding hair, wearing a white collar and a buttoned dark coat, in an oval frame. Inscribed 'Galileus Galileus Florentinus' at top, 'Eques Octavius Leonus' and 'Romanus pictor fecit' at bottom, and dated '16 24' with 'Superiorum licentia'. Printed on cream paper with a grayscale color scale at right.Painting

Primary source

Portrait of Galileo Galilei (1624 print)

1624

Oil portrait of an elderly bearded man with a white collar, wearing a black robe, seated at a table with books, a pair of dividers in his raised hand, and a celestial globe to the left, in a dark background. A brass plaque on the frame reads Galileo Galilei.Painting

Primary source

Oil Portrait of Galileo in His Study

Unknown Italian painter · 18th century (?)

Oval-framed line engraving of an older bearded man in a large white collar and dark doublet, with a Latin inscription above reading Galileus Galileus Florentinus, and an artist credit below. Handwritten Italian caption on mount beneath.Painting

Primary source

Galileo Galilei, line engraving by Ottavio Leoni

Ottavio Leoni · 1624

Title page of a printed book reading 'Lettera del Signor Galileo Galilei Accademico Linceo scritta alla Granduchessa di Toscana', with a decorative floral woodcut ornament and the imprint 'In Fiorenza, MDCXX' at the bottom.Letter

Primary source

Letter to the Grand Duchess Christina

Galileo Galilei · 1615

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